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dBCoolTM Remote Thermal Controller and Voltage Monitor ADT7468
FEATURES
Monitors up to 5 voltages Controls and monitors up to 4 fans High and low frequency fan drive signal 1 on-chip and 2 remote temperature sensors Series resistance cancellation on the remote channel Extended temperature measurement range, up to 191C Dynamic TMIN control mode optimizes system acoustics intelligently Automatic fan speed control mode controls system cooling based on measured temperature Enhanced acoustic mode dramatically reduces user perception of changing fan speeds Thermal protection feature via THERM output Monitors performance impact of Intel(R) PentiumTM 4 processor Thermal control circuit via THERM input 2-wire, 3-wire, and 4-wire fan speed measurement Limit comparison of all monitored values Meets SMBus 2.0 electrical specifications (fully SMBus 1.1 compliant)
GENERAL DESCRIPTION
The ADT7468 dBCOOLTM controller is a thermal monitor and multiple PWM fan controller for noise-sensitive or powersensitive applications requiring active system cooling. The ADT7468 can drive a fan using either a low or high frequency drive signal, monitor the temperature of up to two remote sensor diodes plus its own internal temperature, and measure and control the speed of up to four fans, so that they operate at the lowest possible speed for minimum acoustic noise. The automatic fan speed control loop optimizes fan speed for a given temperature. A unique dynamic TMIN control mode enables the system thermals/acoustics to be intelligently managed. The effectiveness of the system's thermal solution can be monitored using the THERM input. The ADT7468 also provides critical thermal protection to the system using the bidirectional THERM pin as an output to prevent system or component overheating.
FUNCTIONAL BLOCK DIAGRAM
SCL VID5 VID4 VID3 VID2 VID1 VID0 PWM1 PWM2 PWM3 PWM REGISTERS AND CONTROLLERS HF & LF ACOUSTIC ENHANCEMENT CONTROL AUTOMATIC FAN SPEED CONTROL ADDRESS POINTER REGISTER ACOUSTIC ENHANCEMENT CONTROL SERIAL BUS INTERFACE SDA SMBALERT
TACH1 TACH2 TACH3 TACH4 PERFORMANCE MONITORING THERM VCC TO ADT7468 THERMAL PROTECTION FAN SPEED COUNTER
DYNAMIC TMIN CONTROL
PWM CONFIGURATION REGISTERS
INTERRUPT MASKING
INTERRUPT STATUS REGISTERS
VCC D1+ D1- D2+ D2- +5VIN +12VIN +2.5VIN VCCP
ADT7468
10-BIT ADC INPUT SIGNAL CONDITIONING AND ANALOG MULTIPLEXER LIMIT COMPARATORS
SRC
BAND GAP REFERENCE
VALUE AND LIMIT REGISTERS
GND
Figure 1. Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.326.8703 (c) 2004 Analog Devices, Inc. All rights reserved.
04499-0-001
BAND GAP TEMP SENSOR
ADT7468 TABLE OF CONTENTS
Specifications..................................................................................... 3 Absolute Maximum Ratings............................................................ 5 Thermal Characteristics .............................................................. 5 ESD Caution.................................................................................. 5 Pin Configuration and Function Descriptions............................. 6 Typical Performance Characteristics ............................................. 8 Product Description....................................................................... 10 Comparison between ADT7463 and ADT7468 ..................... 10 How to Set the Functionality of Pin 14 ................................... 11 Recommended Implementation............................................... 11 Serial Bus Interface..................................................................... 12 Write Operations ........................................................................ 13 Read Operations ......................................................................... 14 SMBus Timeout .......................................................................... 14 Voltage Measurement Input...................................................... 14 Analog-to-Digital Converter .................................................... 14 Input Circuitry............................................................................ 15 Voltage Measurement Registers................................................ 15 Voltage Limit Registers .............................................................. 15 VID Code Monitoring ............................................................... 15 VID Code Input Threshold Voltage......................................... 15 VID Code Change Detect Function ........................................ 16 Additional ADC Functions for Voltage Measurements ........ 16 Temperature Measurement Method ........................................ 18 Series Resistance Cancellation.................................................. 19 Factors Affecting Diode Accuracy ........................................... 19 Additional ADC Functions for Temperature Measurement. 21 Limits, Status Registers, and Interrupts ....................................... 22 Limit Values................................................................................. 22 Status Registers ........................................................................... 23 THERM Timer ........................................................................... 25 Fan Drive Using PWM Control ............................................... 28 Laying Out 2-Wire and 3-Wire Fans ....................................... 30 Operating from 3.3 V Standby.................................................. 34 XNOR Tree Test Mode .............................................................. 35 Power-On Default ...................................................................... 35 Programming the Automatic Fan Speed Control Loop ............ 36 Automatic Fan Control Overview............................................ 36 Step 1: Hardware Configuration.............................................. 37 Recommended Implementation 1 ........................................... 38 Recommended Implementation 2 ........................................... 39 Step 2: Configuring the MUX................................................... 40 Step 3: TMIN Settings for Thermal Calibration Channels....... 42 Step 4: PWMMIN for Each PWM (Fan) Output....................... 43 Step 5: PWMMAX for PWM (Fan) Outputs.............................. 43 Step 7: TTHERM for Temperature Channels ............................... 47 Step 8: THYST for Temperature Channels .................................. 48 Dynamic TMIN Control Mode ................................................... 49 Step 9: Operating Points for Temperature Channels ............. 51 Step 10: High and Low Limits for Temperature Channels ... 52 Step 11: Monitoring THERM ................................................... 55 Enhancing System Acoustics .................................................... 56 Step 12: Ramp Rate for Acoustic Enhancement..................... 58 Register Tables ................................................................................ 60 ADT7468 Programming Block Diagram .................................... 79 Outline Dimensions ....................................................................... 80 Ordering Guide .......................................................................... 80
REVISION HISTORY
Revision 0: Initial Version
Rev. 0 | Page 2 of 80
ADT7468 SPECIFICATIONS
TA = TMIN to TMAX, VCC = VMIN to VMAX, unless otherwise noted. All voltages are measured with respect to GND, unless otherwise specified. Typicals are at TA = 25C and represent most likely parametric norm. Logic inputs accept input high voltages up to VMAX even when device is operating down to VMIN. Timing specifications are tested at logic levels of VIL = 0.8 V for a falling edge and VIH = 2.0 V for a rising edge. SMBus timing specifications are guaranteed by design and are not production tested. Table 1.
Parameter POWER SUPPLY Supply Voltage Supply Current, ICC TEMP-TO-DIGITAL CONVERTER Local Sensor Accuracy -3.5 -4 Resolution Remote Diode Sensor Accuracy -3.5 -4.5 0.25 6 36 96 ANALOG-TO-DIGITAL CONVERTER (INCLUDING MUX AND ATTENUATORS) Total Unadjusted Error (TUE) Differential Nonlinearity (DNL) Power Supply Sensitivity Conversion Time (Voltage Input) Conversion Time (Local Temperature) Conversion Time (Remote Temperature) Total Monitoring Cycle Time Total Monitoring Cycle Time Input Resistance FAN RPM-TO-DIGITAL CONVERTER Accuracy Resolution Remote Sensor Source Current 0.25 1.5 +2 +2 Min 3.0 Typ 3.3 Max 5.5 3 20 1.5 +2 +2 Unit V mA A C C C C C C C C A % % LSB %/V ms ms ms ms ms k k % % % RPM RPM RPM RPM 94.5 96.3 99 kHz kHz kHz Test Conditions/Comments
Interface inactive, ADC active Standby mode 0C TA 70C -40C TA +100C -40C TA +120C 0C TA 70C; 0C TD 120C -40C TA +100C; 0C TD +120C -40C TA +120C; 0C TD +120C First current Second current Third current For 12 V and 5 V channels For all other channels 8 bits Averaging enabled Averaging enabled Averaging enabled Averaging enabled Averaging disabled For VCC channel For all other channels 0C TA 70C , 3.3 V -40C TA +120C , 3.3 V -40C TA +120C , 5.5 V Fan count = 0xBFFF Fan count = 0x3FFF Fan count = 0x0438 Fan count = 0x021C 0C TA 70C, VCC = 3.3 V -40C TA +120C, VCC = 3.3 V -40C TA +120C, VCC = 5.5 V
2 1.5 1
40 80
0.1 11 12 38 145 19 70 140
100 200 5 7 10 65,535
Full-Scale Count Nominal Input RPM
109 329 5000 10000 85.5 83.7 81 90 90 90
Internal Clock Frequency
Rev. 0 | Page 3 of 80
ADT7468
Parameter Min OPEN-DRAIN DIGITAL OUTPUTS, PWM1 TO PWM3, XTO Current Sink, IOL Output Low Voltage, VOL High Level Output Current, IOH OPEN-DRAIN SERIAL DATA BUS OUTPUT (SDA) Output Low Voltage, VOL High Level Output Current, IOH SMBUS DIGITAL INPUTS (SCL, SDA) Input High Voltage, VIH Input Low Voltage, VIL Hysteresis DIGITAL INPUT LOGIC LEVELS (TACH INPUTS) Input High Voltage, VIH Input Low Voltage, VIL -0.3 Hysteresis DIGITAL INPUT LOGIC LEVELS (THERM) ADTL+ Input High Voltage, VIH Input Low Voltage, VIL DIGITAL INPUT CURRENT Input High Current, IIH Input Low Current, IIL Input Capacitance, CIN SERIAL BUS TIMING Clock Frequency, fSCLK Glitch Immunity, tSW Bus Free Time, tBUF Start Setup Time, tSU;STA Start Hold Time, tHD;STA SCL Low Time, tLOW SCL High Time, tHIGH SCL, SDA Rise Time, tR SCL, SDA Fall Time, tF Data Setup Time, tSU;DAT Data Hold Time, tHD;DAT Detect Clock Low Timeout, tTIMEOUT 0.5 0.75 x VCCP 0.4 -1 1 5 10 4.7 4.7 4.0 4.7 4.0 400 50 2.0 0.4 500 2.0 5.5 0.8 Typ Max 8.0 0.4 1.0 0.4 1.0 Unit mA V A V A V V mV V V V V V p-p V V A A pF kHz ns s s s s s ns s ns ns ms VIN = VCC VIN = 0 See Figure 2 Test Conditions/Comments
0.1
IOUT = -8.0 mA, VCC = +3.3 V VOUT = VCC IOUT = -4.0 mA, VCC = +3.3 V VOUT = VCC
0.1
Maximum input voltage Minimum input voltage
50 1000 300
250 300 15
35
Can be optionally disabled
tLOW
SCL
tR
tF
tHD; STA
tHIGH tHD; STA tHD; DAT tSU; DAT
tSU; STA
tSU; STO
SDA
tBUF
P S
S
P
Figure 2. Serial Bus Timing Diagram
Rev. 0 | Page 4 of 80
04499-0-002
ADT7468 ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Positive Supply Voltage (VCC) Maximum Voltage on 12 VIN Pin Voltage on Any Input or Output Pin Input Current at Any Pin Package Input Current Maximum Junction Temperature (TJMAX) Storage Temperature Range Lead Temperature, Soldering IR Reflow Peak Temperature Lead Temperature (Soldering 10 s) ESD Rating Rating 5.5 V 20 V -0.3 V to +6.5 V 5 mA 20 mA 150C -65C to +150C 220C 300C 1000 V
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
THERMAL CHARACTERISTICS
24-lead QSOP package: JA = 150C/W JC = 39C/W
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
Rev. 0 | Page 5 of 80
ADT7468 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
SDA 1 SCL 2 GND 3 VCC 4 VID0 5 VID1 6
24 23 22 21 20
PWM1/XTO VCCP +2.5VIN +12VIN/VID5 +5VIN/THERM VID4
ADT7468
19
TOP VIEW VID2 7 (NOT TO SCALE) 18 D1+ VID3 8 TACH3 9 PWM2/SMBALERT 10 TACH1
11 17 16 15 14 13
D1- D2+ D2-
04499-0-003
TACH4/GPIO/THERM/SMBALERT PWM3
TACH2 12
Figure 3. Pin Configuration
Table 3. Pin Function Descriptions
Pin No. 1 2 3 4 Mnemonic SDA SCL GND VCC Description Digital I/O (Open Drain). SMBus bidirectional serial data. Requires pull-up resistor. Digital Input (Open Drain). SMBus serial clock input. Requires pull-up resistor. Ground Pin. Power Supply. Can be powered by 3.3 V standby, if monitoring in low power states is required. VCC is also monitored through this pin. The ADT7468 can also be powered from a 5 V supply. Setting Bit 7 of Configuration Register 1 (Reg. 0x40) rescales the VCC input attenuators to correctly measure a 5 V supply. Digital Input (Open Drain). Voltage supply readouts from CPU. This value is read into the VID register (Reg. 0x43). Digital Input (Open Drain). Voltage supply readouts from CPU. This value is read into the VID register (Reg. 0x43). Digital Input (Open Drain). Voltage supply readouts from CPU. This value is read into the VID register (Reg. 0x43). Digital Input (Open Drain). Voltage supply readouts from CPU. This value is read into the VID register (Reg. 0x43). Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 3. Can be reconfigured as an analog input (AIN3) to measure the speed of 2-wire fans. Digital Output (Open Drain). Requires 10 k typical pull-up. Pulse width modulated output to control Fan 2 speed. Can be configured as a high or low frequency drive. Digital Output (Open Drain). This pin can be reconfigured as an SMBALERT interrupt output to signal out-of-limit conditions. Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 1. Can be reconfigured as an analog input (AIN1) to measure the speed of 2-wire fans. Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 2. Can be reconfigured as an analog input (AIN2) to measure the speed of 2-wire fans. Digital I/O (Open Drain). Pulse width modulated output to control speed of Fan 3 and Fan 4. Requires 10 k typical pull-up. Can be configured as a high or low frequency drive. Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 4. Can be reconfigured as an analog input (AIN4) to measure the speed of 2-wire fans. General Purpose Open Drain Digital I/O. Alternatively, the pin can be reconfigured as a bidirectional THERM pin. Can be used to time and monitor assertions on the THERM input. For example, this pin can be connected to the PROCHOT output of an Intel Pentium 4 processor or to the output of a trip point temperature sensor. This pin can also be used as an output to signal overtemperature conditions. Digital Output (Open Drain). This pin can be reconfigured as an SMBALERT interrupt output to signal out-of-limit conditions. Cathode Connection to Second Thermal Diode. Anode Connection to Second Thermal Diode. Cathode Connection to First Thermal Diode.
5 6 7 8 9 10
VID0 VID1 VID2 VID3 TACH3 PWM2 SMBALERT
11 12 13 14
TACH1 TACH2 PWM3 TACH4 GPIO THERM
SMBALERT 15 16 17 D2- D2+ D1-
Rev. 0 | Page 6 of 80
ADT7468
Pin No. 18 19 20 Mnemonic D1+ VID4 +5VIN THERM Description Anode Connection to First Thermal Diode. Digital Input (Open Drain). Voltage supply readouts from CPU. This value is read into the VID register (Reg. 0x43). Analog Input. Monitors +5 V power supply. Alternatively, this pin can be reconfigured as a bidirectional THERM pin. Can be used to time and monitor assertions on the THERM input. For example, it can be connected to the PROCHOT output of an Intel Pentium 4 processor or to the output of a trip point temperature sensor. This pin can also be used as an output to signal overtemperature conditions. Analog Input. Monitors +12 V power supply. Digital Input (Open Drain). Voltage supply readouts from CPU. This value is read into the VID register (Reg. 0x43). Supports VRM10 solutions. Analog Input. Monitors +2.5 V supply, typically a chipset voltage. Analog Input. Monitors processor core voltage (0 V to 3 V). Digital Output (Open Drain). Pulse width modulated output to control Fan 1 speed. Requires 10 k typical pull-up. Also functions as the output from the XOR tree in XOR test mode.
21
+12VIN VID5 +2.5VIN VCCP PWM1 XTO
22 23 24
Rev. 0 | Page 7 of 80
ADT7468 TYPICAL PERFORMANCE CHARACTERISTICS
0
20
100mV
-10
15
TEMPERATURE ERROR (C)
TEMPERATURE ERROR (C)
-20
10
40mV
-30
5
-40
0
-50
-5
60mV
-60 0 1 2.2 3.3 CAPACITANCE (nF) 4.7 10
-10 10
100
1M 10M FREQUENCY (kHz)
100M
1G
Figure 4. Temperature Error vs. Capacitance between D+ and D-
Figure 7. Remote Temperature Error vs. Common Mode Noise Frequency
0 -10 -20
6 5 4
TEMPERATURE ERROR (C)
20mV
TEMPERATURE ERROR (C)
-30 -40 -50 -60 -70 -80 -90
04499-0-046
3 2 1 0 -1 -2 -3 -4 10
04499-0-049 04499-0-050
10mV
-100 0 5 10 15 CAPACITANCE (nF) 20 25
100
1M 10M FREQUENCY (kHz)
100M
1G
Figure 5. External Temperature Error vs. D+/D- Capacitance
Figure 8. Remote Temperature Error vs. Differential Mode Noise Frequency
60
D+ TO GND
1.40 1.35 1.30 1.25 1.20 1.15 1.10
04499-0-047
40
TEMPERATURE ERROR (C)
20 0 -20 -40 -60 -80 0 1 3.3 10 RESISTANCE (M) 20 100
D+ TO VCC
IDD (mA)
1.05 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 5.4 POWER SUPPLY VOLTAGE (V)
Figure 6. Remote Temperature Error vs. PCB Resistance
Figure 9. Normal IDD vs. Power Supply
Rev. 0 | Page 8 of 80
04499-0-048
04499-0-045
ADT7468
7 6 0 5 4 3 2 1 -3.5 0 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 5.4 POWER SUPPLY VOLTAGE (V)
04499-0-051
1.0 0.5
-0.5
ERROR (C)
-1.0 -1.5 -2.0 -2.5 -3.0
IDD (A)
-4.0 -40
-20
0
20 40 60 TEMPERATURE (C)
80
100
120
Figure 10. Shutdown IDD vs. Power Supply
Figure 13. Internal Temperature Error vs. ADT7468 Temperature
1.0
20 15
TEMPERATURE ERROR (C)
0.5 0
INT ERROR, 250mV
10 5 0 -5 -10 -15 -20 10
-0.5
ERROR (C)
-1.0 -1.5 -2.0 -2.5 -3.0
INT ERROR, 100mV
-3.5 -4.0 -40
04499-0-092
100 1M 10M 100M POWER SUPPLY NOISE FREQUENCY (kHz)
1G
04499-0-052
-20
0
20 40 60 TEMPERATURE (C)
80
100
120
Figure 14. Remote Temperature Error vs. ADT7468 Temperature Figure 11. Internal Temperature Error vs. Power Supply
20
EXT ERROR, 250mV
15
TEMPERATURE ERROR (C)
10 5 0
EXT ERROR, 100mV
-5 -10 -15 -20 10
04499-0-053
100 1M 10M 100M POWER SUPPLY NOISE FREQUENCY (kHz)
1G
Figure 12. Remote Temperature Error vs. Power Supply Noise Frequency
Rev. 0 | Page 9 of 80
04499-0-091
ADT7468 PRODUCT DESCRIPTION
The ADT7468 is a complete thermal monitor and multiple fan controller for any system requiring thermal monitoring and cooling. The device communicates with the system via a serial system management bus. The serial bus controller has a serial data line for reading and writing addresses and data (Pin 1), and an input line for the serial clock (Pin 2). All control and programming functions for the ADT7468 are performed over the serial bus. In addition, a pin can be reconfigured as an SMBALERT output to signal out-of-limit conditions. 5. The ADT7468 has an extended temperature measurement range. The measurement range goes from-64C to +191C. On the ADT7463, the measurement range is from -127C to +127C. This means that the ADT7468 can measure higher temperatures. The ADT7468 also includes the ADT7463 temperature range; the temperature measurement range can be switched by setting Bit 0 of Configuration Register 5. The ADT7468 maximum fan speed (% duty cycle) in the automatic fan speed control loop can be programmed. The maximum fan speed is 100% duty cycle on the ADT7463 and is not programmable. The offset register in the ADT7468 is programmable up to 64C with 0.50C resolution. The offset register of the ADT7463 is programmable up to 32C with 0.25C resolution. VCCP is monitored on Pin 23 of the ADT7468 and can be used to set the threshold for THERM (PROCHOT) (2/3 of VCCP). The threshold for THERM (PROCHOT) is set at VIH = 1.7 V and VIL = 0.8 V on the ADT7463. On the ADT7463, Pin 22 can be reconfigured as SMBus ALERT. This is not available on the ADT7468; instead, SMBALERT can be enabled on Pin 14.
6.
COMPARISON BETWEEN ADT7463 AND ADT7468
The ADT7468 is an upgrade to the ADT7463. The ADT7468 and ADT7463 are almost pin and register map compatible. The ADT7468 and ADT7463 have the following differences: 1. On the ADT7468, the PWM drive signals can be configured as either high frequency or low frequency drives. The low frequency option is programmable between 10 Hz and 100 Hz. The high frequency option is 22.5 kHz. On the ADT7463, only the low frequency option is available. Once the VCC is powered up, monitoring of temperature and fan speeds is enabled on the ADT7468 when VCCP is powered up, or if VCCP is never powered up, when the first SMBus transaction with the ADT7468 is completed. On the ADT7463, the STRT bit in Configuration Register 1 must be set to enable monitoring. The fans are switched off by default on power-up on the ADT7468. On the ADT7463, the fans run at full speed on power-up. Fail-safe cooling is provided on the ADT7468 in that, if the measured temperature exceeds the THERM limit (100C), the fans run at full speed. Fail-safe cooling is also provided 4.6 s after VCCP is powered up. See Figure 48. The fans go to full speed, if the ADT7468 has not been addressed via the SMBus within 4.6 s of when the VCCP is powered up. This protects the system in the event that the SMBus fails. The ADT7468 can be programmed at any time, either before or after the 4.6 s has elapsed, and it behaves as programmed. If VCCP is never powered up, fail-safe cooling is effectively disabled. If VCCP is disabled, writing to the ADT7468 at any time causes the ADT7468 to operate normally. 4. Series resistance cancellation (SRC) is provided on the remote temperature channels on the ADT7468, but not on the ADT7463. SRC automatically cancels linear offset introduced by a series resistance between the thermal diode and the sensor.
7.
8.
2.
9.
3.
10. A GPIO can also be made available on Pin 14 on the ADT7468. This is not available on the ADT7463. Set the GPIO polarity and direction in Configuration Register 5. The GPIO status bit is Bit 5 of Status Register 2 (shared with TACH4 and THERM, because only one can be enabled at a time). 11. The ADT7463 has three possible SMBus addresses, which are selectable using the address select and address enable pins. The ADT7468 has one SMBus address available at Address 0x2E. Due to the inclusion of extra functionality, the register map has changed, including an additional configuration register: Configuration Register 5 at Address 0x7C. Configuration Register 5 Bit 0: If Bit 0 is set to 1, the ADT7468 is backward compatible temperature-wise with the ADT7463. Measurements, TMIN calibration circuit, fan control, etc., work in the range -127C to +127C. Also, care should be taken in reprogramming the temperature limits (TMIN, operating point, THERM limits) to their desired twos complement value, because the power-on default for them is at Offset 64. The extended temperature range is -64C to 191C. The default is 1, which is in the -64C to +191C temperature range.
Rev. 0 | Page 10 of 80
ADT7468
Bit 1= 0 is the high frequency (22.5 kHz) fan drive signal. Bit 1 = 1 switches the fan drive to low frequency PWM, programmable between 10 Hz and 100 Hz, the same as the ADT7463. The default = 0 = HF PWM. Bit 2 sets the direction for the GPIO: 0 = input, 1 = output. Bit 3 sets the GPIO polarity: 0 = active low, 1 = active high. * * * * *
RECOMMENDED IMPLEMENTATION
Configuring the ADT7468 as in Figure 15 allows the system designer to use the following features: * Two PWM outputs for fan control of up to three fans (the front and rear chassis fans are connected in parallel). Three TACH fan speed measurement inputs. VCC measured internally through Pin 3. CPU temperature measured using Remote 1 temperature channel. Ambient temperature measured through Remote 2 temperature channel. Bidirectional THERM pin. This feature allows Intel Pentium 4 PROCHOT monitoring and can function as an overtemperature THERM output. It can alternatively be programmed as an SMBALERT system interrupt output.
HOW TO SET THE FUNCTIONALITY OF PIN 14
Pin 14 on the ADT7468 has four possible functions: SMBALERT, THERM, GPIO, and TACH4. The user chooses the required functionality by setting Bit 0 and Bit 1 of Configuration Register 4 at Address 0x7D. Table 4. Pin 14 Settings
Bit 0 00 01 10 11 Bit 1 Function TACH4 THERM SMBALERT GPIO
CPU FAN FRONT CHASSIS FAN
ADT7468
TACH2 PWM1 TACH1
REAR CHASSIS FAN
PWM3 TACH3 VID[0:4]/VID[0:5] D2+ D2- THERM
5(VRM9)/6(VRM10)
AMBIENT TEMPERATURE
D1+ D1-
PROCHOT
CPU
3.3VSB 5V 12V/VID5 ADP316x VRM CONTROLLER VCOMP CURRENT VCORE SDA SCL SMBALERT GND ICH
04499-0-004
Figure 15. ADT7468 Configuration
Rev. 0 | Page 11 of 80
ADT7468
SERIAL BUS INTERFACE
On PCs and servers, control of the ADT7468 is carried out using the serial system management bus (SMBus). The ADT7468 is connected to this bus as a slave device, under the control of a master controller, which is usually (but not necessarily) the ICH. The ADT7468 has a fixed 7-bit serial bus address of 0101110 or 0x2E. The read/write bit must be added to get the 8-bit address (01011100 or 0x5C). Data is sent over the serial bus in sequences of nine clock pulses: eight bits of data followed by an acknowledge bit from the slave device. Transitions on the data line must occur during the low period of the clock signal and remain stable during the high period, because a low-to-high transition when the clock is high might be interpreted as a stop signal. The number of data bytes that can be transmitted over the serial bus in a single read or write operation is limited only by what the master and slave devices can handle. When all data bytes have been read or written, stop conditions are established. In write mode, the master pulls the data line high during the tenth clock pulse to assert a stop condition. In read mode, the master device overrides the acknowledge bit by pulling the data line high during the low period before the ninth clock pulse. This is known as No Acknowledge. The master then takes the data line low during the low period before the tenth clock pulse, and then high during the tenth clock pulse to assert a stop condition. Any number of bytes of data can be transferred over the serial bus in one operation, but it is not possible to mix read and write in one operation, because the type of operation is determined at the beginning and cannot subsequently be changed without starting a new operation. In the ADT7468, write operations contain either one or two bytes, and read operations contain one byte and perform the following functions. To write data to one of the device data registers or read data from it, the address pointer register must be set so that the correct data register is addressed, then data can be written into that register or read from it. The first byte of a write operation always contains an address that is stored in the address pointer register. If data is to be written to the device, then the write operation contains a second data byte that is written to the register selected by the address pointer register. This write operation is illustrated in Figure 16. The device address is sent over the bus, and then R/W is set to 0. This is followed by two data bytes. The first data byte is the address of the internal data register to be written to, which is stored in the address pointer register. The second data byte is the data to be written to the internal data register. When reading data from a register, there are two possibilities: * If the ADT7468's address pointer register value is unknown or not the desired value, it must first be set to the correct value before data can be read from the desired data register. This is done by performing a write to the ADT7468 as before, but only the data byte containing the register address is sent, because no data is written to the register. This is shown in Figure 17. A read operation is then performed consisting of the serial bus address, R/W bit set to 1, followed by the data byte read from the data register. This is shown in Figure 18. * If the address pointer register is known to be already at the desired address, data can be read from the corresponding data register without first writing to the address pointer register, as shown in Figure 18.
1 SCL
9
1
9
SDA START BY MASTER
0
1
0
1
1
1
0
R/W ACK. BY ADT7468
D7
D6
D5
D4
D3
D2
D1
D0 ACK. BY ADT7468
FRAME 1 SERIAL BUS ADDRESS BYTE
FRAME 2 ADDRESS POINTER REGISTER BYTE
1 SCL (CONTINUED)
9
SDA (CONTINUED)
D7
D6
D5
D4
D3
D2
D1
D0
04499-0-005
FRAME 3 DATA BYTE
ACK. BY ADT7468
STOP BY MASTER
Figure 16. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register
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ADT7468
1 SCL 9 1 9
SDA START BY MASTER
0
1
0
1
1
1
0
R/W ACK. BY ADT7468
D7
D6
D5
D4
D3
D2
D1
D0
04499-0-006
04499-0-007
FRAME 1 SERIAL BUS ADDRESS BYTE
FRAME 2 ADDRESS POINTER REGISTER BYTE
ACK. BY ADT7468
STOP BY MASTER
Figure 17. Writing to the Address Pointer Register Only
1 SCL
9
1
9
SDA START BY MASTER
0
1
0
1
1
1
0
R/W ACK. BY ADT7468
D7
D6
D5
D4
D3
D2
D1
D0 NO ACK. BY STOP BY MASTER MASTER
FRAME 1 SERIAL BUS ADDRESS BYTE
FRAME 2 DATA BYTE FROM ADT7468
Figure 18. Reading Data from a Previously Selected Register
It is possible to read a data byte from a data register without first writing to the address pointer register, if the address pointer register is already at the correct value. However, it is not possible to write data to a register without writing to the address pointer register, because the first data byte of a write is always written to the address pointer register. In addition to supporting the send byte and receive byte protocols, the ADT7468 also supports the read byte protocol. (see System Management Bus Specifications Rev. 2 for more information. This document is available from Intel.) If several read or write operations must be performed in succession, the master can send a repeat start condition instead of a stop condition to begin a new operation.
2. 3. 4. 5. 6.
The master sends the 7-bit slave address followed by the write bit (low). The addressed slave device asserts ACK on SDA. The master sends a command code. The slave asserts ACK on SDA. The master asserts a stop condition on SDA and the transaction ends.
For the ADT7468, the send byte protocol is used to write a register address to RAM for a subsequent single byte read from the same address. This operation is illustrated in Figure 19.
1 2 3 4 REGISTER ADDRESS 56 AP
04499-0-008
WRITE OPERATIONS
The SMBus specification defines several protocols for different types of read and write operations. The ones used in the ADT7468 are discussed below. The following abbreviations are used in the diagrams: S - START P - STOP R - READ W - WRITE A - ACKNOWLEDGE A - NO ACKNOWLEDGE The ADT7468 uses the following SMBus write protocols. Send Byte In this operation, the master device sends a single command byte to a slave device as follows: 1. The master device asserts a start condition on SDA.
SLAVE S WA ADDRESS
Figure 19. Setting a Register Address for Subsequent Read
If the master is required to read data from the register immediately after setting up the address, it can assert a repeat start condition immediately after the final ACK and carry out a single byte read without asserting an intermediate stop condition. Write Byte In this operation, the master device sends a command byte and one data byte to the slave device, as follows: 1. 2. 3. 4. The master device asserts a start condition on SDA. The master sends the 7-bit slave address followed by the write bit (low). The addressed slave device asserts ACK on SDA. The master sends a command code.
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ADT7468
5. 6. 7. 8. The slave asserts ACK on SDA. The master sends a data byte. The slave asserts ACK on SDA. The master asserts a stop condition on SDA to end the transaction. 3. 1. 2. SMBALERT is pulled low. The master initiates a read operation and sends the alert response address (ARA = 0001 100). This is a general call address that must not be used as a specific device address. The device whose SMBALERT output is low responds to the alert response address, and the master reads its device address. The address of the device is now known and can be interrogated in the usual way. If more than one device's SMBALERT output is low, the one with the lowest device address has priority in accordance with normal SMBus arbitration. Once the ADT7468 has responded to the alert response address, the master must read the status registers and the SMBALERT is cleared only if the error condition has gone away.
This operation is illustrated in Figure 20.
1 2 3 4 SLAVE ADDRESS 5 6 78
04499-0-009
SLAVE S WA ADDRESS
A DATA A P
4.
Figure 20. Single Byte Write to a Register
READ OPERATIONS
The ADT7468 uses the following SMBus read protocols. Receive Byte This operation is useful when repeatedly reading a single register. The register address must have been set up previously. In this operation, the master device receives a single byte from a slave device as follows: 1. 2. 3. 4. 5. 6. The master device asserts a start condition on SDA. The master sends the 7-bit slave address followed by the read bit (high). The addressed slave device asserts ACK on SDA. The master receives a data byte. The master asserts NO ACK on SDA. The master asserts a stop condition on SDA and the transaction ends.
5.
SMBUS TIMEOUT
The ADT7468 includes an SMBus timeout feature. If there is no SMBus activity for 35 ms, the ADT7468 assumes that the bus is locked and releases the bus. This prevents the device from locking or holding the SMBus expecting data. Some SMBus controllers cannot handle the SMBus timeout feature, so it can be disabled. Configuration Register 1(Reg. 0x40) <6> TODIS = 0, SMBus timeout enabled (default). <6> TODIS = 1, SMBus timeout disabled.
VOLTAGE MEASUREMENT INPUT
The ADT7468 has four external voltage measurement channels. It can also measure its own supply voltage, VCC. Pins 20 to 23 can measure 5 V, 12 V, and 2.5 V supplies, and the processor core voltage VCCP (0 V to 3 V input). The VCC supply voltage measurement is carried out through the VCC pin (Pin 4). Setting Bit 7 of Configuration Register 1 (Reg. 0x40) allows a 5 V supply to power the ADT7468 and be measured without overranging the VCC measurement channel. The 2.5 V input can be used to monitor a chipset supply voltage in computer systems.
In the ADT7468, the receive byte protocol is used to read a single byte of data from a register whose address has previously been set by a send byte or write byte operation. This operation is illustrated in Figure 21.
1 2 3 4 5 6
04499-0-010
SLAVE S RA ADDRESS
DATA A P
Figure 21. Single Byte Read from a Register
ANALOG-TO-DIGITAL CONVERTER
Alert Response Address Alert response address (ARA) is a feature of SMBus devices that allows an interrupting device to identify itself to the host when multiple devices exist on the same bus. The SMBALERT output can be used as either an interrupt output or an SMBALERT. One or more outputs can be connected to a common SMBALERT line connected to the master. If a device's SMBALERT line goes low, the following procedure occurs: All analog inputs are multiplexed into the on-chip, successiveapproximation, analog-to-digital converter. This has a resolution of 10 bits. The basic input range is 0 V to 2.25 V, but the inputs have built-in attenuators to allow measurement of 2.5 V, 3.3 V, 5 V, 12 V, and the processor core voltage VCCP without any external components. To allow for the tolerance of these supply voltages, the ADC produces an output of 3/4 full scale (decimal 768 or 300 hex) for the nominal input voltage and so has adequate headroom to cope with overvoltages.
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ADT7468
INPUT CIRCUITRY
The internal structure for the analog inputs is shown in Figure 22. The input circuit consists of an input protection diode, an attenuator, plus a capacitor to form a first-order lowpass filter that gives input immunity to high frequency noise.
12VIN 120k 20k 30pF
Reg. 0x4C, 12 V Low Limit = 0x00 default Reg. 0x4D, 12 V High Limit = 0xFF default Table 5 shows the input ranges of the analog inputs and output codes of the 10-bit ADC. When the ADC is running, it samples and converts a voltage input in 0.7 ms and averages 16 conversions to reduce noise; a measurement takes nominally 11 ms.
5VIN
93k 47k 30pF
VID CODE MONITORING
The ADT7468 has five dedicated voltage ID (VID code) inputs. These are digital inputs that can be read back through the VID register (Reg. 0x43) to determine the processor voltage required or being used in the system. Five VID code inputs support VRM9.x solutions. In addition, Pin 21 (12 V input) can be reconfigured as a sixth VID input to satisfy future VRM requirements. VID Code Register (Reg. 0x43)
04499-0-011
3.3VIN
68k 71k 30pF MUX
2.5VIN
45k 94k 30pF
VCCP
17.5k 52.5k 35pF
<0> = VID0, reflects logic state of Pin 5. <1> = VID1, reflects logic state of Pin 6. <2> = VID2, reflects logic state of Pin 7.
Figure 22. Structure of Analog Inputs
VOLTAGE MEASUREMENT REGISTERS
Reg. 0x20, 2.5 V Reading = 0x00 default Reg. 0x21, VCCP Reading = 0x00 default Reg. 0x22, VCC Reading = 0x00 default Reg. 0x23, 5 V Reading = 0x00 default Reg. 0x24, 12 V Reading = 0x00 default
<3> = VID3, reflects logic state of Pin 8. <4> = VID4, reflects logic state of Pin 19. <5> = VID5, reconfigurable 12 V input. This bit reads 0 when Pin 21 is configured as the 12 V input. This bit reflects the logic state of Pin 21 when the pin is configured as VID5.
VID CODE INPUT THRESHOLD VOLTAGE
The switching threshold for the VID code inputs is approximately 1 V. To enable future compatibility, it is possible to reduce the VID code input threshold to 0.6 V. Bit 6 (THLD) of the VID register (Reg. 0x43) controls the VID input threshold voltage. VID CODE REGISTER (Reg. 0x43) <6> THLD = 0, VID switching threshold = 1 V, VOL < 0.8 V, VIH > 1.7 V, VMAX = 3.3 V THLD = 1, VID switching threshold = 0.6 V, VOL < 0.4 V, VIH > 0.8 V, VMAX = 3.3 V Reconfiguring Pin 21 as VID5 Input Pin 21 can be reconfigured as a sixth VID code input (VID5) for VRM10 compatible systems. Because the pin is configured as VID5, it is not possible to monitor a 12 V supply. Bit 7 of the VID register (Reg. 0x43) determines the function of Pin 21. System or BIOS software can read the state of Bit 7 to determine whether the system is designed to monitor 12 V or is monitoring a sixth VID input.
VOLTAGE LIMIT REGISTERS
Associated with each voltage measurement channel is a high and low limit register. Exceeding the programmed high or low limit causes the appropriate status bit to be set. Exceeding either limit can also generate SMBALERT interrupts. Reg. 0x44, 2.5 V Low Limit = 0x00 default Reg. 0x45, 2.5 V High Limit = 0xFF default Reg. 0x46, VCCP Low Limit = 0x00 default Reg. 0x47, VCCP High Limit = 0xFF default Reg. 0x48, VCC Low Limit = 0x00 default Reg. 0x49, VCC High Limit = 0xFF default Reg. 0x4A, 5 V Low Limit = 0x00 default Reg. 0x4B, 5 V High Limit = 0xFF default
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ADT7468
VID Code Register (Reg. 0x43) <7> VIDSEL = 0, Pin 21 functions as a 12 V measurement input. Software can read this bit to determine that there are five VID inputs being monitored. Bit 5 of Register 0x43 (VID5) always reads back 0. Bit 0 of Status Register 2 (Reg. 0x42) reflects 12 V out-of-limit measurements. VIDSEL = 1, Pin 21 functions as the sixth VID code input (VID5). Software can read this bit to determine that there are six VID inputs being monitored. Bit 5 of Register 0x43 reflects the logic state of Pin 21. Bit 0 of Status Register 2 (Reg. 0x42) reflects VID code changes. instances where faster conversions are needed, setting Bit 4 of Configuration Register 2 (Reg. 0x73) turns averaging off. This effectively gives a reading 16 times faster (0.7 ms), but the reading may be noisier. Bypass Voltage Input Attenuator Setting Bit 5 of Configuration Register 2 (Reg. 0x73) removes the attenuation circuitry from the 2.5 V, VCCP, VCC, 5 V, and 12 V inputs. This allows the user to directly connect external sensors or rescale the analog voltage measurement inputs for other applications. The input range of the ADC without the attenuators is 0 V to 2.25 V. Single-Channel ADC Conversion Setting Bit 6 of Configuration Register 2 (Reg. 0x73) places the ADT7468 into single-channel ADC conversion mode. In this mode, the ADT7468 can be made to read a single voltage channel only. If the internal ADT7468 clock is used, the selected input is read every 0.7 ms. The appropriate ADC channel is selected by writing to Bits <7:5> of the TACH1 minimum high byte register (0x55).
Bits <7:5> Reg. 0x55 000 001 010 011 100 101 110 111 Channel Selected 2.5 V VCCP VCC 5V 12 V Remote 1 Temperature Local Temperature Remote 2 Temperature
VID CODE CHANGE DETECT FUNCTION
The ADT7468 has a VID code change detect function. When Pin 21 is configured as the VID5 input, VID code changes can be detected and reported back by the ADT7468. Bit 0 of Status Register 2 (Reg. 0x42) is the 12 V/VC bit and denotes a VID change when set. The VID code change bit is set when the logic states on the VID inputs are different than they were 11 s previously. The change of VID code can be used to generate an SMBALERT interrupt. If an SMBALERT interrupt is not required, Bit 0 of Interrupt Mask Register 2 (Reg. 0x75), when set, prevents SMBALERTs from occurring on VID code changes. Status Register 2 (Reg. 0x42) <0> 12V/VC = 0, if Pin 21 is configured as VID5, then Logic 0 denotes no change in VID code within the last 11 s. <0> 12V/VC = 1, if Pin 21 is configured as VID5, then Logic 1 means that a change has occurred on the VID code inputs within the last 11 s. An SMBALERT is generated, if this function is enabled.
Configuration Register 2 (Reg. 0x73) <4> = 1, averaging off. <5> = 1, bypass input attenuators. <6> = 1, single-channel convert mode. TACH1 Minimum High Byte (Reg. 0x55) <7:5> Selects ADC channel for single-channel convert mode.
ADDITIONAL ADC FUNCTIONS FOR VOLTAGE MEASUREMENTS
A number of other functions are available on the ADT7468 to offer the system designer increased flexibility. Turn-Off Averaging For each voltage measurement read from a value register, 16 readings have actually been made internally and the results averaged before being placed into the value register. For
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ADT7468
Table 5. 10-Bit A/D Output Code vs. VIN
12 VIN <0.0156 0.0156-0.0312 0.0312-0.0469 0.0469-0.0625 0.0625-0.0781 0.0781-0.0937 0.0937-0.1093 0.1093-0.1250 0.1250-0.1406 5 VIN <0.0065 0.0065-0.0130 0.0130-0.0195 0.0195-0.0260 0.0260-0.0325 0.0325-0.0390 0.0390-0.0455 0.0455-0.0521 0.0521-0.0586 * * * 1.6675-1.6740 * * * 3.3300-3.3415 * * * 5.0025-5.0090 * * * 6.5983-6.6048 6.6048-6.6113 6.6113-6.6178 6.6178-6.6244 6.6244-6.6309 6.6309-6.6374 6.6374-6.4390 6.6439-6.6504 6.6504-6.6569 6.6569-6.6634 >6.6634 Input Voltage VCC (3.3 VIN)1 <0.0042 0.0042-0.0085 0.0085-0.0128 0.0128-0.0171 0.0171-0.0214 0.0214-0.0257 0.0257-0.0300 0.0300-0.0343 0.0343-0.0386 2.5 VIN <0.0032 0.0032-0.0065 0.0065-0.0097 0.0097-0.0130 0.0130-0.0162 0.0162-0.0195 0.0195-0.0227 0.0227-0.0260 0.0260-0.0292 VCCP <0.00293 0.0293-0.0058 0.0058-0.0087 0.0087-0.0117 0.0117-0.0146 0.0146-0.0175 0.0175-0.0205 0.0205-0.0234 0.0234-0.0263 Decimal 0 1 2 3 4 5 6 7 8 A/D Output Binary (10 Bits) 00000000 00 00000000 01 00000000 10 00000000 11 00000001 00 00000001 01 00000001 10 00000001 11 00000010 00
4.0000-4.0156
1.1000-1.1042
0.8325-0.8357
0.7500-0.7529
256 (1/4 scale)
01000000 00
8.0000-8.0156
2.2000-2.2042
1.6650-1.6682
1.5000-1.5029
512 (1/2 scale)
10000000 00
12.0000-12.0156
3.3000-3.3042
2.4975-2.5007
2.2500-2.2529
768 (3/4 scale)
11000000 00
15.8281-15.8437 15.8437-15.8593 15.8593-15.8750 15.8750-15.8906 15.8906-15.9062 15.9062-15.9218 15.9218-15.9375 15.9375-15.9531 15.9531-15.9687 15.9687-15.9843 >15.9843
4.3527-4.3570 4.3570-4.3613 4.3613-4.3656 4.3656-4.3699 4.3699-4.3742 4.3742-4.3785 4.3785-4.3828 4.3828-4.3871 4.3871-4.3914 4.3914-4.3957 >4.3957
3.2942-3.2974 3.2974-3.3007 3.3007-3.3039 3.3039-3.3072 3.3072-3.3104 3.3104-3.3137 3.3137-3.3169 3.3169-3.3202 3.3202-3.3234 3.3234-3.3267 >3.3267
2.9677-2.9707 2.9707-2.9736 2.9736-2.9765 2.9765-2.9794 2.9794-2.9824 2.9824-2.9853 2.9853-2.9882 2.9882-2.9912 2.9912-2.9941 2.9941-2.9970 >2.9970
1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023
11111101 01 11111101 10 11111101 11 11111110 00 11111110 01 11111110 10 11111110 11 11111111 00 11111111 01 11111111 10 11111111 11
1 The VCC output codes listed assume that VCC is 3.3 V. If VCC input is reconfigured for 5 V operation (by setting Bit 7 of Configuration Register 1), then the VCC output codes are the same as for the 5 VIN column.
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ADT7468
TEMPERATURE MEASUREMENT METHOD
A simple method of measuring temperature is to exploit the negative temperature coefficient of a diode, measuring the baseemitter voltage (VBE) of a transistor, operated at constant current. Unfortunately, this technique requires calibration to null out the effect of the absolute value of VBE, which varies from device to device. The technique used in the ADT7468 is to measure the change in VBE when the device is operated at three different currents. Previous devices have used only two operating currents, but the use of a third current allows automatic cancellation of resistances in series with the external temperature sensor. Figure 24 shows the input signal conditioning used to measure the output of an external temperature sensor. This figure shows the external sensor as a substrate transistor, but it could equally be a discrete transistor. If a discrete transistor is used, the collector is not grounded and should be linked to the base. To prevent ground noise from interfering with the measurement, the more negative terminal of the sensor is not referenced to ground, but is biased above ground by an internal diode at the D- input. C1 can optionally be added as a noise filter (recommended maximum value 1000 pF). However, a better option in noisy environments is to add a filter, as described in the Noise Filtering section. Local Temperature Measurement The ADT7468 contains an on-chip band gap temperature sensor whose output is digitized by the on-chip 10-bit ADC. The 8-bit MSB temperature data is stored in the local temperature register (Address 26h). Because both positive and negative temperatures can be measured, the temperature data is stored in Offset 64 format or twos complement format, as shown in Table 6 and Table 7. Theoretically, the temperature sensor and ADC can measure temperatures from -128C to +127C (or -61C to +191C in the extended temperature range) with a resolution of 0.25C. However, this exceeds the operating temperature range of the device, so local temperature measurements outside the ADT7468 operating temperature range are not possible. Remote Temperature Measurement The ADT7468 can measure the temperature of two remote diode sensors or diode-connected transistors connected to Pins 17 and 18, or 15 and 16. The forward voltage of a diode or diode-connected transistor operated at a constant current exhibits a negative temperature coefficient of about -2 mV/C. Unfortunately, the absolute value of VBE varies from device to device and individual calibration is required to null this out, so the technique is unsuitable for mass production. The technique used in the ADT7468 is to measure the change in VBE when the device is operated at three different currents. This is given by
V BE = KT / q x 1n( N ) where: K is Boltzmann's constant. q is the charge on the carrier. T is the absolute temperature in Kelvin. N is the ratio of the two currents. Figure 23 shows the input signal conditioning used to measure the output of a remote temperature sensor. This figure shows the external sensor as a substrate transistor, provided for temperature monitoring on some microprocessors. It could also be a discrete transistor such as a 2N3904/2N3906.
I N2 x I N1 x I IBIAS VDD
REMOTE SENSING TRANSISTOR D+ LPF fC = 65kHz VOUT+ TO ADC D- VOUT-
04499-0-012
Figure 23. Signal Conditioning for Remote Diode Temperature Sensors
If a discrete transistor is used, the collector is not grounded and should be linked to the base. If a PNP transistor is used, the base is connected to the D- input and the emitter to the D+ input. If an NPN transistor is used, the emitter is connected to the D- input and the base to the D+ input. Figure 25 and Figure 26 show how to connect the ADT7468 to an NPN or PNP transistor for temperature measurement. To prevent ground noise from interfering with the measurement, the more negative terminal of the sensor is not referenced to ground, but is biased above ground by an internal diode at the D- input. To measure VBE, the operating current through the sensor is switched among three related currents. Shown in Figure 23, N1 x I and N2 x I are different multiples of the current I. The currents through the temperature diode are switched between I and N1 x I, giving VBE1, and then between I and N2 x I, giving VBE2. The temperature can then be calculated using the two VBE measurements. This method can also cancel the effect of any series resistance on the temperature measurement. The resulting VBE waveforms are passed through a 65 kHz low-pass filter to remove noise and then to a chopper-stabilized amplifier. This amplifies and rectifies the waveform to produce a dc voltage proportional to VBE. The ADC digitizes this voltage, and a temperature measurement is produced. To reduce the effects of noise, digital filtering is performed by averaging the results of 16 measurement cycles.
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ADT7468
The results of remote temperature measurements are stored in 10-bit, twos complement format, as illustrated in Table 6. The extra resolution for the temperature measurements is held in the Extended Resolution Register 2 (Reg. 0x77). This gives temperature readings with a resolution of 0.25C.
Noise Filtering
FACTORS AFFECTING DIODE ACCURACY
Remote Sensing Diode
For temperature sensors operating in noisy environments, previous practice was to place a capacitor across the D+ and D- pins to help combat the effects of noise. However, large capacitances affect the accuracy of the temperature measurement, leading to a recommended maximum capacitor value of 1000 pF. This capacitor reduces the noise, but does not eliminate it, making use the sensor difficult in a very noisy environment. The ADT7468 has a major advantage over other devices for eliminating the effects of noise on the external sensor. Using the series resistance cancellation feature, a filter can be constructed between the external temperature sensor and the part. The effect of any filter resistance seen in series with the remote sensor is automatically canceled from the temperature result. The construction of a filter allows the ADT7468 and the remote temperature sensor to operate in noisy environments. Figure 24 shows a low-pass R-C-R filter, with the following values : R = 100 , C = 1 nF. This filtering reduces both common-mode noise and differential noise.
100 D+ 1nF 100 D-
04499-0-093
The ADT7468 is designed to work with either substrate transistors built into processors or with discrete transistors. Substrate transistors are generally PNP types with the collector connected to the substrate. Discrete types can be either PNP or NPN transistors connected as a diode (base-shorted to the collector). If an NPN transistor is used, the collector and base are connected to D+ and the emitter to D-. If a PNP transistor is used, the collector and base are connected to D- and the emitter is connected to D+. To reduce the error due to variations in both substrate and discrete transistors, a number of factors should be taken into consideration: * The ideality factor, nf, of the transistor is a measure of the deviation of the thermal diode from ideal behavior. The ADT7468 is trimmed for an nf value of 1.008. Use the following equation to calculate the error introduced at a temperature T (C), when using a transistor whose nf does not equal 1.008. See the processor data sheet for the nf values.
T = (nf - 1.008) x (273.15 K + T)
To factor this in, the user can write the T value to the offset register. The ADT7468 then automatically adds it to or subtracts it from the temperature measurement. * Some CPU manufacturers specify the high and low current levels of the substrate transistors. The high current level of the ADT7468, IHIGH, is 96 A and the low level current, ILOW, is 6 A. If the ADT7468 current levels do not match the current levels specified by the CPU manufacturer, it might be necessary to remove an offset. The CPUs data sheet advises whether this offset needs to be removed and how to calculate it. This offset can be programmed to the offset register. It is important to note that, if more than one offset must be considered, the algebraic sum of these offsets must be programmed to the offset register.
REMOTE TEMPERATURE SENSOR
Figure 24. Filter Between Remote Sensor and ADT7468
SERIES RESISTANCE CANCELLATION
Parasitic resistance to the ADT7468 D+ and D- inputs (seen in series with the remote diode) is caused by a variety of factors, including PCB track resistance and track length. This series resistance appears as a temperature offset in the remote sensor's temperature measurement. This error typically causes a 0.5C offset per of parasitic resistance in series with the remote diode. The ADT7468 automatically cancels out the effect of this series resistance on the temperature reading, giving a more accurate result, without the need for user characterization of this resistance. The ADT7468 is designed to automatically cancel, typically, up to 3 k of resistance. By using an advanced temperature measurement method, this is transparent to the user. This feature allows resistances to be added to the sensor path to produce a filter, allowing the part to be used in noisy environments. See the Noise Filtering section for details.
If a discrete transistor is used with the ADT7468, the best accuracy is obtained by choosing devices according to the following criteria: * * * * Base-emitter voltage greater than 0.25 V at 6 A, at the highest operating temperature. Base-emitter voltage less than 0.95 V at 100 A, at the lowest operating temperature. Base resistance less than 100 . Small variation in hFE (say 50 to 150) that indicates tight control of VBE characteristics.
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ADT7468
Transistors, such as 2N3904, 2N3906, or equivalents in SOT-23 packages, are suitable devices to use.
Table 6. Temperature Data Format
Temperature -128C -125C -100C -75C -50C -25C -10C 0C 10.25C 25.5C 50.75C 75C 100C 125C 127C Digital Output (10-Bit)1 1000 0000 00 1000 0011 00 1001 1100 00 1011 0101 00 1100 1110 00 1110 0111 00 1111 0110 00 0000 0000 00 0000 1010 01 0001 1001 10 0011 0010 11 0100 1011 00 0110 0100 00 0111 1101 00 0111 1111 00
Nulling Out Temperature Errors
As CPUs run faster, it is getting more difficult to avoid high frequency clocks when routing the D+/D- traces around a system board. Even when recommended layout guidelines are followed, some temperature errors may still be attributable to noise coupled onto the D+/D- lines. Constant high frequency noise usually attenuates or increases temperature measurements by a linear, constant value. The ADT7468 has temperature offset registers at Addresses 0x70, 0x72 for the Remote 1 and Remote 2 temperature channels. By doing a one-time calibration of the system, the user can determine the offset caused by system board noise and null it out using the offset registers. The offset registers automatically add an Offset 64/twos complement 8-bit reading to every temperature measurement. The LSBs add 0.5C offset to the temperature reading so the 8-bit register effectively allows temperature offsets of up to 64C with a resolution of 0.5C. This ensures that the readings in the temperature measurement registers are as accurate as possible.
Temperature Offset Registers
1 Bold numbers denote 2 LSB of measurement in Extended Resolution Register 2 (Reg. 0x77) with 0.25C resolution.
Reg. 0x70, Remote 1 Temperature Offset = 0x00 (0C default) Reg. 0x71, Local Temperature Offset = 0x00 (0C default) Reg. 0x72, Remote 2 Temperature Offset = 0x00 (0C default)
ADT7463/ADT7468 Backwards Compatible Mode
Table 7. Extended Range, Temperature Data Format
Temperature -64C -1C 0C 1C 10C 25C 50C 75C 100C 125C 191C
1
Digital Output (10-Bit)1 0000 0000 00 0011 1111 00 0100 0000 00 0100 0001 00 0100 1010 00 0101 1001 00 0111 0010 00 1000 1001 00 1010 0100 00 1011 1101 00 1111 1111 00
Bold numbers denote 2 LSB of measurement in Extended Resolution Register 2 (Reg. 0x77) with 0.25C resolution.
By setting Bit 1 of Configuration Register 5 (0x7C), all temperature measurements are stored in the Zone Temp value registers (0x25, 0x26, and 0x27) in twos complement in the range -64C to +127C (the ADT7468 still makes calculations based on the Offset 64 extended range and clamps the results, if necessary.) The temperature limits must be reprogrammed in twos complement. If a twos complement temperature below -63C is entered, the temperature is clamped to -63C. In this mode, the diode fault condition remains -128C = 1000 0000, while in the extended temperature range (-64C to +191C), the fault condition is represented by -64C = 0000 0000.
Temperature Measurement Registers
ADT7468
2N3904 NPN D+
04499-0-013
Reg. 0x25, Remote 1 Temperature Reg. 0x26, Local Temperature Reg. 0x27, Remote 2 Temperature Reg. 0x77, Extended Resolution 2 = 0x00 default
<7:6> TDM2, Remote 2 temperature LSBs. <5:4> LTMP, local temperature LSBs.
D-
Figure 25. Measuring Temperature Using an NPN Transistor
ADT7468
2N3906 PNP D+
04499-0-014
<3:2> TDM1, Remote 1 temperature LSBs.
D-
Figure 26. Measuring Temperature Using a PNP Transistor
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ADT7468
Temperature Measurement Limit Registers Table 9. Conversion Time with Averaging Enabled
Channel Voltage Channels Remote Temperature Local Temperature Measurement Time 11 ms 39 ms 12 ms
Associated with each temperature measurement channel are high and low limit registers. Exceeding the programmed high or low limit causes the appropriate status bit to be set. Exceeding either limit can also generate SMBALERT interrupts. Reg. 0x4E, Remote 1 Temperature Low Limit = 0x01 default Reg. 0x4F, Remote 1 Temperature High Limit = 0x7F default Reg. 0x50, Local Temperature Low Limit = 0x01 default Reg. 0x51, Local Temperature High Limit = 0x7F default Reg. 0x52, Remote 2 Temperature Low Limit = 0x01 default Reg. 0x53, Remote 2 Temperature High Limit = 0x7F default
Reading Temperature from the ADT7468
Single-Channel ADC Conversions
Setting Bit 6 of Configuration Register 2 (Reg. 0x73) places the ADT7468 into single-channel ADC conversion mode. In this mode, the ADT7468 can be made to read a single temperature channel only. The appropriate ADC channel is selected by writing to Bits <7:5> of the TACH1 minimum high byte register (0x55).
Table 10. Channel Selection
Bits <7:5> Reg. 0x55 101 110 111 Channel Selected Remote 1 temperature Local temperature Remote 2 temperature
It is important to note that temperature can be read from the ADT7468 as an 8-bit value (with 1C resolution) or as a 10-bit value (with 0.25C resolution). If only 1C resolution is required, the temperature readings can be read back at any time and in no particular order. If the 10-bit measurement is required, this involves a 2-register read for each measurement. The extended resolution register (Reg. 0x77) should be read first. This causes all temperature reading registers to be frozen until all temperature reading registers have been read from. This prevents an MSB reading from being updated while its two LSBs are being read and vice versa.
Configuration Register 2 (Reg. 0x73) <4> = 1, averaging off. <6> = 1, single-channel convert mode. TACH1 Minimum High Byte (Reg. 0x55) <7:5> selects ADC channel for single-channel convert mode. Overtemperature Events
ADDITIONAL ADC FUNCTIONS FOR TEMPERATURE MEASUREMENT
A number of other functions are available on the ADT7468 to offer the system designer increased flexibility.
Turn-Off Averaging
For each temperature measurement read from a value register, 16 readings have actually been made internally and the results averaged before being placed into the value register. Sometimes it is necessary to take a very fast measurement. Setting Bit 4 of Configuration Register 2 (Reg. 0x73) turns averaging off.
Table 8. Conversion Time with Averaging Disabled
Channel Voltage Channels Remote Temperature 1 Remote Temperature 2 Local Temperature Measurement Time 0.7 ms 7 ms 7 ms 1.3 ms
Overtemperature events on any of the temperature channels can be detected and dealt with automatically in automatic fan speed control mode. Register 0x6A to Register 0x6C are the THERM temperature limits. When a temperature exceeds its THERM temperature limit, all PWM outputs run at the maximum PWM duty cycle (Reg. 0x38, Reg. 0x39, and Reg. 0x3A). This effectively runs the fans at the fastest allowed speed. The fans stay running at this speed until the temperature drops below THERM minus hysteresis. (This can be disabled by setting the boost bit in Configuration Register 3, Bit 2, Reg. 0x78.) The hysteresis value for that THERM temperature limit is the value programmed into Reg. 0x6D and Reg. 0x6E (hysteresis registers). The default hysteresis value is 4C.
THERM LIMIT
HYSTERESIS (C)
TEMPERATURE
FANS
Figure 27. THERM Temperature Limit Operation
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100%
ADT7468 LIMITS, STATUS REGISTERS, AND INTERRUPTS
LIMIT VALUES
Associated with each measurement channel on the ADT7468 are high and low limits. These can form the basis of system status monitoring; a status bit can be set for any out-of-limit condition and detected by polling the device. Alternatively, SMBALERT interrupts can be generated to flag a processor or microcontroller of out-of-limit conditions.
8-Bit Limits THERM Limit Register
Reg. 0x7A, THERM Limit = 0x00 default
16-Bit Limits
The following is a list of 8-bit limits on the ADT7468.
Voltage Limit Registers
The fan TACH measurements are 16-bit results. The fan TACH limits are also 16 bits, consisting of a high byte and low byte. Because fans running under speed or stalled are normally the only conditions of interest, only high limits exist for fan TACHs. Because the fan TACH period is actually being measured, exceeding the limit indicates a slow or stalled fan.
Fan Limit Registers
Reg. 0x44, 2.5 V Low Limit = 0x00 default Reg. 0x45, 2.5 V High Limit = 0xFF default Reg. 0x46, VCCP Low Limit = 0x00 default Reg. 0x47, VCCP High Limit = 0xFF default Reg. 0x48, VCC Low Limit = 0x00 default Reg. 0x49, VCC High Limit = 0xFF default Reg. 0x4A, 5 V Low Limit = 0x00 default Reg. 0x4B, 5 V High Limit = 0xFF default Reg. 0x4C, 12 V Low Limit = 0x00 default Reg. 0x4D, 12 V High Limit = 0xFF default Reg. 0x46, VCCP Low Limit = 0x00 default Reg. 0x47, VCCP High Limit = 0xFF default Reg. 0x48, VCC Low Limit = 0x00 default Reg. 0x49, VCC High Limit = 0xFF default
Temperature Limit Registers
Reg. 0x54, TACH1 Minimum Low Byte = 0x00 default Reg. 0x55, TACH1 Minimum High Byte = 0x00 default Reg. 0x56, TACH2 Minimum Low Byte = 0x00 default Reg. 0x57, TACH2 Minimum High Byte = 0x00 default Reg. 0x58, TACH3 Minimum Low Byte = 0x00 default Reg. 0x59, TACH3 Minimum High Byte = 0x00 default Reg. 0x5A, TACH4 Minimum Low Byte = 0x00 default Reg. 0x5B, TACH4 Minimum High Byte = 0x00 default
Out-of-Limit Comparisons
Once all limits have been programmed, the ADT7468 can be enabled for monitoring. The ADT7468 measures all voltage and temperature measurements in round-robin format and sets the appropriate status bit for out-of-limit conditions. TACH measurements are not part of this round-robin cycle. Comparisons are done differently depending on whether the measured value is being compared to a high or low limit.
High Limit: > Comparison Performed Low Limit: Comparison Performed
Reg. 0x4E, Remote 1 Temperature Low Limit = 0x01 default Reg. 0x4F, Remote 1 Temperature High Limit = 0x7F default Reg. 0x6A, Remote 1 THERM Limit = 0x64 default Reg. 0x50, Local Temperature Low Limit = 0x01 default Reg. 0x51, Local Temperature High Limit = 0x7F default Reg. 0x6B, Local THERM Limit = 0x64 default Reg. 0x52, Remote 2 Temperature Low Limit = 0x01 default Reg. 0x53, Remote 2 Temperature High Limit = 0x7F default Reg. 0x6C, Remote 2 THERM Limit = 0x64 default
Voltage and temperature channels use a window comparator for error detecting and, therefore, have high and low limits. Fan speed measurements use only a low limit. This fan limit is needed only in manual fan control mode.
Analog Monitoring Cycle Time
The analog monitoring cycle begins when a 1 is written to the start bit (Bit 0) of Configuration Register 1 (Reg. 0x40). By default, the ADT7463 powers up with this bit set. The ADC measures each analog input in turn and, as each measurement is completed, the result is automatically stored in the appropriate value register. This round-robin monitoring cycle continues unless disabled by writing a 0 to Bit 0 of Configuration Register 1.
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ADT7468
As the ADC is normally left to free-run in this manner, the time taken to monitor all the analog inputs is normally not of interest, because the most recently measured value of any input can be read out at any time. For applications where the monitoring cycle time is important, it can easily be calculated. The total number of channels measured is * * * * Four dedicated supply voltage inputs Supply voltage (VCC pin) Local temperature Two remote temperatures
Status Register 1 (Reg. 0x41) Bit 7 (OOL) = 1, denotes a bit in Status Register 2 is set and Status Register 2 should be read. Bit 6 (R2T) = 1, Remote 2 temperature high or low limit has been exceeded. Bit 5 (LT) = 1, local temperature high or low limit has been exceeded. Bit 4 (R1T) = 1, Remote 1 temperature high or low limit has been exceeded. Bit 3 (5 V) = 1, 5 V high or low limit has been exceeded. Bit 2 (VCC) = 1, VCC high or low limit has been exceeded. Bit 1 (VCCP) = 1, VCCP high or low limit has been exceeded. Bit 0 (2.5 V) = 1, 2.5 V high or low limit has been exceeded. Status Register 2 (Reg. 0x42) Bit 7 (D2) = 1, indicates an open or short on D2+/D2- inputs. Bit 6 (D1) = 1, indicates an open or short on D1+/D1- inputs. Bit 5 (F4P) = 1, indicates Fan 4 has dropped below minimum speed. Alternatively, indicates that the THERM limit has been exceeded, if the THERM function is used. Bit 4 (FAN3) = 1, indicates Fan 3 has dropped below minimum speed. Bit 3 (FAN2) = 1, indicates Fan 2 has dropped below minimum speed. Bit 2 (FAN1) = 1, indicates Fan 1 has dropped below minimum speed. Bit 1 (OVT) = 1, indicates a THERM overtemperature limit has been exceeded. Bit 0 (12V/VC) = 1, indicates a 12 V high or low limit has been exceeded. If the VID code change function is used, this bit indicates a change in VID code on the VID0 to VID5 inputs. SMBALERT Interrupt Behavior
As mentioned previously, the ADC performs round-robin conversions and takes 11 ms for each voltage measurement, 12 ms for a local temperature reading, and 39 ms for each remote temperature reading. The total monitoring cycle time for averaged voltage and temperature monitoring is, therefore, nominally (5 x 11) + 12 + (2 x 39) = 145 ms Fan TACH measurements are made in parallel and are not synchronized with the analog measurements in any way.
STATUS REGISTERS
The results of limit comparisons are stored in Status Registers 1 and 2. The status register bit for each channel reflects the status of the last measurement and limit comparison on that channel. If a measurement is within limits, the corresponding status register bit is cleared to 0. If the measurement is out-of-limits, the corresponding status register bit is set to 1. The state of the various measurement channels can be polled by reading the status registers over the serial bus. In Bit 7 (OOL) of Status Register 1 (Reg. 0x41), 1 means that an out-of-limit event has been flagged in Status Register 2. This means that the user also needs to read Status Register 2. Alternatively, Pin 10 or Pin 14 can be configured as an SMBALERT output. This hard interrupt automatically notifies the system supervisor of an outof-limit condition. Reading the status registers clears the appropriate status bit as long as the error condition that caused the interrupt has cleared. Status register bits are "sticky." Whenever a status bit is set, indicating an out-of-limit condition, it remains set even if the event that caused it has gone away (until read). The only way to clear the status bit is to read the status register after the event has gone away. Interrupt status mask registers (Reg. 0x74, and Reg. 0x75) allow individual interrupt sources to be masked from causing an SMBALERT. However, if one of these masked interrupt sources goes out-oflimit, its associated status bit is set in the interrupt status registers.
The ADT7468 can be polled for status, or an SMBALERT interrupt can be generated for out-of-limit conditions. It is important to note how the SMBALERT output and status bits behave when writing interrupt handler software.
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ADT7468
HIGH LIMIT
HIGH LIMIT
TEMPERATURE
TEMPERATURE
CLEARED ON READ (TEMP BELOW LIMIT)
"STICKY" STATUS BIT TEMP BACK IN LIMIT (STATUS BIT STAYS SET) SMBALERT
"STICKY" STATUS BIT
CLEARED ON READ (TEMP BELOW LIMIT) TEMP BACK IN LIMIT (STATUS BIT STAYS SET)
04499-0-022
SMBALERT
Figure 28. SMBALERT and Status Bit Behavior
INTERRUPT MASK BIT CLEARED (SMBALERT REARMED)
Figure 28 shows how the SMBALERT output and "sticky" status bits behave. Once a limit is exceeded, the corresponding status bit is set to 1. The status bit remains set until the error condition subsides and the status register is read. The status bits are referred to as "sticky," because they remain set until read by software. This ensures that an out-of-limit event cannot be missed, if software is polling the device periodically. Note that the SMBALERT output remains low for the entire duration that a reading is out-of-limit and until the status register has been read. This has implications on how software handles the interrupt.
Handling SMBALERT Interrupts
Figure 29. How Masking the Interrupt Source Affects SMBALERT Output
Interrupt Mask Register 1 (Reg. 0x74) Bit 7 (OOL) = 1, masks SMBALERT for any alert condition flagged in Status Register 2. Bit 6 (R2T) = 1, masks SMBALERT for Remote 2 temperature. Bit 5 (LT) = 1, masks SMBALERT for local temperature. Bit 4 (R1T) = 1, masks SMBALERT for Remote 1 temperature. Bit 3 (5 V) = 1, masks SMBALERT for 5 V channel. Bit 2 (VCC) = 1, masks SMBALERT for VCC channel. Bit 0 (VCCP) = 1, masks SMBALERT for VCCP channel. Interrupt Mask Register 2 (Reg. 0x75) Bit 7 (D2) = 1, masks SMBALERT for Diode 2 errors. Bit 6 (D1) = 1, masks SMBALERT for Diode 1 errors. Bit 5 (FAN4) = 1, masks SMBALERT for Fan 4 failure.
To prevent the system from being tied up servicing interrupts, it is recommend to handle the SMBALERT interrupt as follows: 1. 2. 3. 4. Detect the SMBALERT assertion. Enter the interrupt handler. Read the status registers to identify the interrupt source. Mask the interrupt source by setting the appropriate mask bit in the interrupt mask registers (Reg. 0x74 and Reg. 0x75). Take the appropriate action for a given interrupt source. Exit the interrupt handler. Periodically poll the status registers. If the interrupt status bit has cleared, reset the corresponding interrupt mask bit to 0. This causes the SMBALERT output and status bits to behave as shown in Figure 29.
5. 6. 7.
If the TACH4 pin is being used as the THERM input, this bit masks SMBALERT for a THERM event.
Bit 4 (FAN3) = 1, masks SMBALERT for Fan 3. Bit 3 (FAN2) = 1, masks SMBALERT for Fan 2. Bit 2 (FAN1) = 1, masks SMBALERT for Fan 1. Bit 1 (OVT) = 1, masks SMBALERT for overtemperature (exceeding THERM temperature limits). Bit 0 (12V/VC) = 1, masks SMBALERT for 12 V channel or for a VID code change, depending on the function used.
Masking Interrupt Sources
Interrupt Mask Registers 1 and 2 are located at Addresses 0x74 and 0x75. These allow individual interrupt sources to be masked out to prevent SMBALERT interrupts. Note that masking an interrupt source prevents only the SMBALERT output from being asserted; the appropriate status bit is set normally.
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INTERRUPT MASK BIT SET
ADT7468
Enabling the SMBALERT Interrupt Output
The SMBALERT interrupt function is disabled by default. Pin 10 or Pin 14 can be reconfigured as an SMBALERT output to signal out-of-limit conditions.
Table 11. Configuring Pin 10 as SMBALERT Output
Register Configuration Register 3 (Reg. 0x78) Bit Setting <0> Pin 10 = ALERT <1> Pin 10 = PWM2
below TMIN or if the duty cycle in manual mode is set to 0x00, then pulling the THERM low externally has no effect. See Figure 30 for more information.
TMIN
THERM
Assigning THERM Functionality to a Pin
Pin 14 on the ADT7468 has four possible functions: SMBALERT, THERM, GPIO, and TACH4. The user chooses the required functionality by setting Bit 0 and Bit 1 of Configuration Register 4 at Address 0x7D. If THERM is enabled (Bit 1, Configuration Register 3 at Address 0x78): * * Pin 20 becomes THERM. If Pin 14 is configured as THERM (Bit 0 and Bit 1 of Configuration Register 4 at Address 0x7D), then THERM is enabled on this pin.
THERM ASSERTED TO LOW AS AN INPUT: FANS DO NOT GO TO 100%, BECAUSE TEMPERATURE IS BELOW TMIN THERM ASSERTED TO LOW AS AN INPUT: FANS DO NOT GO TO 100%, BECAUSE TEMPERATURE IS ABOVE TMIN AND FANS ARE ALREADY RUNNING
04499-0-024
Figure 30. Asserting THERM Low as an Input in Automatic Fan Speed Control Mode
THERM TIMER
The ADT7468 has an internal timer to measure THERM assertion time. For example, the THERM input can be connected to the PROCHOT output of a Pentium 4 CPU to measure system performance. The THERM input can also be connected to the output of a trip point temperature sensor. The timer is started on the assertion of the ADT7468's THERM input and stopped when THERM is unasserted. The timer counts THERM times cumulatively, that is, the timer resumes counting on the next THERM assertion. The THERM timer continues to accumulate THERM assertion times until the timer is read (it is cleared on read) or until it reaches full scale. If the counter reaches full scale, it stops at that reading until cleared. The 8-bit THERM timer register (Reg. 0x79) is designed such that Bit 0 is set to 1 on the first THERM assertion. Once the cumulative THERM assertion time has exceeded 45.52 ms, Bit 1 of the THERM timer is set and Bit 0 now becomes the LSB of the timer with a resolution of 22.76 ms (see Figure 31). When using the THERM timer, be aware of the following. After a THERM timer read (Reg. 0x79): 1. 2. The contents of the timer are cleared on read. The F4P bit (Bit 5) of Status Register 2 needs to be cleared (assuming that the THERM timer limit has been exceeded).
If THERM is not enabled: * * Pin 20 becomes a 5 V measurement input. If Pin 14 is configured as THERM, then THERM is disabled on this Pin.
Bit 1 0 1 0 1 Function TACH4 THERM SMBALERT GPIO
Table 12. Configuring Pin 14
Bit 0 0 0 1 1
THERM as an Input
When THERM is configured as an input, the user can time assertions on the THERM pin. This can be useful for connecting to the PROCHOT output of a CPU to gauge system performance. The user can also set up the ADT7468 so that, when the THERM pin is driven low externally, the fans run at 100%. The fans run at 100% for the duration of the time that the THERM pin is pulled low. This is done by setting the BOOST bit (Bit 2) in Configuration Register 3 (Address = 0x78) to 1. This works only if the fan is already running, for example, in manual mode when the current duty cycle is above 0x00, or in automatic mode when the temperature is above TMIN. If the temperature is
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ADT7468
If the THERM timer is read during a THERM assertion, then the following happens: 1. 2. The contents of the timer are cleared. Bit 0 of the THERM timer is set to 1 (because a THERM assertion is occurring). The THERM timer increments from zero. If the THERM timer limit (Reg. 0x7A) = 0x00, then the F4P bit is set.
THERM
THERM TIMER (REG. 0x79)
00000001 76543210 THERM ASSERTED 22.76ms
THERM
3. 4.
ACCUMULATE THERM LOW ASSERTION TIMES THERM TIMER (REG. 0x79) 00000010 76543210 THERM ASSERTED 45.52ms
Generating SMBALERT Interrupts from THERM Timer Events
The ADT7468 can generate SMBALERTs when a programmable THERM timer limit has been exceeded. This allows the system designer to ignore brief, infrequent THERM assertions, while capturing longer THERM timer events. Register 0x7A is the THERM timer limit register. This 8-bit register allows a limit from 0 s (first THERM assertion) to 5.825 s to be set before an SMBALERT is generated. The THERM timer value is compared with the contents of the THERM timer limit register. If the THERM timer value exceeds the THERM timer limit value, then the F4P bit (Bit 5) of Status Register 2 is set and an SMBALERT is generated. Note that the F4P bit (Bit 5) of Mask Register 2 (Reg. 0x75) masks out SMBALERTs, if this bit is set to 1; although the F4P bit of Interrupt Status Register 2 still is set, if the THERM timer limit is exceeded.
THERM
ACCUMULATE THERM LOW ASSERTION TIMES
04499-0-025
THERM TIMER (REG. 0x79)
00000101 7 6 5 4 3 2 1 0 THERM ASSERTED 113.8ms (91.04ms + 22.76ms)
Figure 31.Understanding the THERM Timer
Figure 32 is a functional block diagram of the THERM timer, limit, and associated circuitry. Writing a value of 0x00 to the THERM timer limit register (Reg. 0x7A) causes SMBALERT to be generated on the first THERM assertion. A THERM timer limit value of 0x01 generates an SMBALERT, once cumulative THERM assertions exceed 45.52 ms.
THERM LIMIT (REG. 0x7A)
2.914s 1.457s 728.32ms 364.16ms 182.08ms 91.04ms 45.52ms 22.76ms
2.914s 1.457s 728.32ms 364.16ms THERM TIMER (REG. 0x79) 182.08ms 91.04ms 45.52ms 22.76ms
01234567
76543210
THERM THERM TIMER CLEARED ON READ
COMPARATOR
IN
OUT LATCH RESET
F4P BIT (BIT 5) STATUS REGISTER 2
SMBALERT
CLEARED ON READ
1 = MASK F4P BIT (BIT 5) MASK REGISTER 2 (REG. 0x75)
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Figure 32. Functional Block Diagram of THERM Monitoring Circuitry
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ADT7468
Configuring the Relevant THERM Behavior
1.
Configure the desired pin as the THERM timer input. Setting Bit 1 (THERM timer enable) of Configuration Register 3 (Reg. 0x78) enables the THERM timer monitoring functionality. This is disabled on Pins 14 and 20 by default. Setting Bits 0 and 1 (PIN14FUNC) of Configuration Register 4 (Reg. 0x7D) enables THERM timer output functionality on Pin 20 (Bit 1 of Configuration Register 3, THERM, must also be set). Pin 14 can also be used as TACH4.
can be calculated for a fixed THERM timer limit time. For example, if it takes one week for a THERM timer limit of 2.914 s to be exceeded and the next time it takes only 1 hour, then this is an indication of a serious degradation in system performance.
Configuring the THERM Pin as an Output
2.
Select the desired fan behavior for THERM timer events. Assuming that the fans are running, setting Bit 2 (BOOST bit) of Configuration Register 3 (Reg. 0x78) causes all fans to run at 100% duty cycle whenever THERM is asserted. This allows fail-safe system cooling. If this bit is 0, the fans run at their current settings and are not affected by THERM events. If the fans are not already running when THERM is asserted, the fans do not run to full speed.
In addition to monitoring THERM as an input, the ADT7468 can optionally drive THERM low as an output. In cases where PROCHOT is bidirectional, THERM can be used to throttle the processor by asserting PROCHOT. The user can preprogram system-critical thermal limits. If the temperature exceeds a thermal limit by 0.25C, THERM asserts low. If the temperature is still above the thermal limit on the next monitoring cycle, THERM stays low. THERM remains asserted low until the temperature is equal to or below the thermal limit. Because the temperature for that channel is measured only once for every monitoring cycle, after THERM asserts it is guaranteed to remain low for at least one monitoring cycle. The THERM pin can be configured to assert low, if the Remote 1, local, or Remote 2 THERM temperature limits are exceeded by 0.25C. The THERM temperature limit registers are at Registers 0x6A, 0x6B, and 0x6C, respectively. Setting Bit 3 of Registers 0x5F, 0x60, and 0x61 enables the THERM output feature for the Remote 1, local, and Remote 2 temperature channels, respectively. Figure 33 shows how the THERM pin asserts low as an output in the event of a critical overtemperature.
THERM LIMIT +0.25C THERM LIMIT
3.
Select whether THERM timer events should generate SMBALERT interrupts. Bit 5 (F4P) of Mask Register 2 (Reg. 0x75), when set, masks out SMBALERTs when the THERM timer limit value is exceeded. This bit should be cleared, if SMBALERTs based on THERM events are required.
4.
Select a suitable THERM limit value. This value determines whether an SMBALERT is generated on the first THERM assertion, or only if a cumulative THERM assertion time limit is exceeded. A value of 0x00 causes an SMBALERT to be generated on the first THERM assertion.
TEMP
THERM
This value specifies how often OS or BIOS level software checks the THERM timer. For example, BIOS could read the THERM timer once an hour to determine the cumulative THERM assertion time. If, for example, the total THERM assertion time is <22.76 ms in Hour 1, >182.08 ms in Hour 2, and >5.825 s in Hour 3, this can indicate that system performance is degrading significantly, because THERM is asserting more frequently on an hourly basis. Alternatively, OS or BIOS level software can timestamp when the system is powered on. If an SMBALERT is generated due to the THERM timer limit being exceeded, another timestamp can be taken. The difference in time
ADT7468 MONITORING CYCLE
Figure 33. Asserting THERM as an Output, Based on Tripping THERM Limits
An alternative method of disabling THERM is to program the THERM temperature limit to -64C or less in Offset 64 mode, or -128C or less in twos complement mode; that is, for THERM temperature limit values less than -63C or -128C, respectively, THERM is disabled.
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04499-0-027
5.
Select a THERM monitoring time.
ADT7468
FAN DRIVE USING PWM CONTROL
The ADT7468 uses pulse-width modulation (PWM) to control fan speed. This relies on varying the duty cycle (or on/off ratio) of a square wave applied to the fan to vary the fan speed. The external circuitry required to drive a fan using PWM control is extremely simple. For 4-wire fans, the PWM drive might need only a pull-up resistor. In many cases, the 4-wire fan PWM input has a built-in pull-up resistor. The ADT7468 PWM frequency can be set to a selection of low frequencies or a single high PWM frequency. The low frequency options are usually used for 2-wire and 3-wire fans, while the high frequency option is usually used with 4-wire fans. For 2-wire or 3-wire fans, a single N-channel MOSFET is the only drive device required. The specifications of the MOSFET depend on the maximum current required by the fan being driven and the input capacitance of the FET. Because a 10 k (or greater) resistor must be used as a PWM pull-up, an FET with large input capacitance can cause the PWM output to become distorted and adversely affect the fan control range. This is a requirement only when using high frequency PWM mode. Typical notebook fans draw a nominal 170 mA, and so SOT devices can be used where board space is a concern. In desktops, fans can typically draw 250 mA to 300 mA each. If you drive several fans in parallel from a single PWM output or drive larger server fans, the MOSFET must handle the higher current requirements. The only other stipulation is that the MOSFET should have a gate voltage drive, VGS < 3.3 V, for direct interfacing to the PWM_OUT pin. VGS can be greater than 3.3 V as long as the pull-up on the gate is tied to 5 V. The MOSFET should also have a low on resistance to ensure that there is not significant voltage drop across the FET, which would reduce the voltage applied across the fan and, therefore, the maximum operating speed of the fan. Figure 34 shows how to drive a 3-wire fan using PWM control.
12V 12V
Figure 34 uses a 10 k pull-up resistor for the TACH signal. This assumes that the TACH signal is an open-collector from the fan. In all cases, the TACH signal from the fan must be kept below 5 V maximum to prevent damaging the ADT7468. If in doubt as to whether the fan used has an open-collector or totem-pole TACH output, use one of the input signal conditioning circuits shown in the Fan Speed Measurement section. Figure 35 shows a fan drive circuit using an NPN transistor such as a general-purpose MMBT2222. While these devices are inexpensive, they tend to have much lower current handling capabilities and higher on resistance than MOSFETs. When choosing a transistor, care should be taken to ensure that it meets the fan's current requirements. Ensure that the base resistor is chosen such that the transistor is saturated when the fan is powered on. Because 4-wire fans are powered continuously, the fan speed is not switched on or off as with previous PWM driven/powered fans. This enables it to perform better than 3-wire fans, especially for high frequency applications.
12V 12V
10k TACH 10k 4.7k 3.3V TACH 12V FAN 1N4148
ADT7468
665 PWM Q1 MMBT2222
Figure 35. Driving a 3-Wire Fan Using an NPN Transistor
Figure 36 shows a typical drive circuit for 4-wire fans.
12V 12V 12V, 4-WIRE FAN 10k TACH/AIN 10k 4.7k 3.3V TACH VCC TACH PWM
10k TACH/AIN 10k 4.7k 3.3V 12V FAN 1N4148
ADT7468
2k PWM
04499-0-041
ADT7468
10k PWM Q1 NDT3055L
04499-0-028
Figure 36. Driving a 4-Wire Fan
Figure 34. Driving a 3-Wire Fan Using an N-Channel MOSFET
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04499-0-029
ADT7468
Driving Two Fans from PWM3 Driving up to Three Fans from PWM3
The ADT7468 has four TACH inputs available for fan speed measurement, but only three PWM drive outputs. If a fourth fan is being used in the system, it should be driven from the PWM3 output in parallel with the third fan. Figure 37 shows how to drive two fans in parallel using low cost NPN transistors. Figure 38 shows the equivalent circuit using a MOSFET. Because the MOSFET can handle up to 3.5 A, it is simply a matter of connecting another fan directly in parallel with the first. Care should be taken in designing drive circuits with transistors and FETs to ensure that the PWM pins are not required to source current and that they sink less than the 5 mA maximum current specified on the data sheet.
TACH measurements for fans are synchronized to particular PWM channels; for example, TACH1 is synchronized to PWM1. TACH3 and TACH4 are both synchronized to PWM3, so PWM3 can drive two fans. Alternatively, PWM3 can be programmed to synchronize TACH2, TACH3, and TACH4 to the PWM3 output. This allows PWM3 to drive two or three fans. In this case, the drive circuitry looks the same, as shown in Figure 37 and Figure 38. The SYNC bit in Register 0x62 enables this function. Synchronization is not required in high frequency mode when used with 4-wire fans.
<4> (SYNC) Enhance Acoustics Register 1 (Reg. 0x62) SYNC = 1, synchronizes TACH2, TACH3, and TACH4 to PWM3.
12V
ADT7468
3.3V
3.3V TACH3 1N4148 TACH4
1k PWM3 2.2k Q1 MMBT3904 10
Q2 MMBT2222
Q3 MMBT2222
Figure 37. Interfacing Two Fans in Parallel to the PWM3 Output Using Low Cost NPN Transistors
3.3V 10k TYPICAL TACH4 3.3V +V +V
ADT7468
TACH3
10k TYPICAL TACH 5V OR 12V FAN 1N4148 TACH 5V OR 12V FAN
3.3V
10k TYPICAL PWM3
04499-0-031
Q1 NDT3055L
Figure 38. Interfacing Two Fans in Parallel to the PWM3 Output Using a Single N-Channel MOSFET
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10
ADT7468
Driving 2-Wire Fans
The ADT7468 can support 2-wire fans only when low frequency PWM mode is selected in Configuration Register 5, Bit 2. If this bit is not set to 1, the ADT7468 cannot measure the speed of 2-wire fans. Figure 39 shows how a 2-wire fan can be connected to the ADT7468. This circuit allows the speed of a 2-wire fan to be measured, even though the fan has no dedicated TACH signal. A series resistor, RSENSE, in the fan circuit converts the fan commutation pulses into a voltage, which is ac-coupled into the ADT7468 through the 0.01 F capacitor. On-chip signal conditioning allows accurate monitoring of fan speed. The value of RSENSE chosen depends upon the programmed input threshold and the current drawn by the fan. For fans drawing approximately 200 mA, a 2 RSENSE value is suitable when the threshold is programmed as 40 mV.
+V
For fans that draw more current, such as larger desktop or server fans, RSENSE can be reduced for the same programmed threshold. The smaller the threshold programmed the better, because more voltage is developed across the fan and the fan spins faster. Note that when the voltage spikes (either negative going or positive going) are more than 40 mV in amplitude, the fan speed can be reliably determined.
LAYING OUT 2-WIRE AND 3-WIRE FANS
Figure 41 shows how to lay out a common circuit arrangement for 2-wire and 3-wire fans. Some components are not populated, depending on whether a 2-wire or 3-wire fan is used.
12V OR 5V R1
1N4148 3.3V OR 5V
R2
R5 PWM C1
ADT7468
3.3V
5V OR 12V FAN
1N4148
TACH R3
Q1 MMBT2222 R4 FOR 3-WIRE FANS: POPULATE R1, R2, R3 R4 = 0W C1 = UNPOPULATED FOR 2-WIRE FANS: POPULATE R4, C1 R1, R2, R3 UNPOPULATED
04499-0-042
10k TYPICAL PWM Q1 NDT3055L
0.01F
04499-0-032
Figure 41. Planning for 2-Wire or 3-Wire Fans on a PCB
RSENSE 2 TYPICAL
TACH
TACH Inputs
Figure 39. Driving a 2-Wire Fan
Pins 9, 11, 12, and 14 (when configured as TACH inputs) are open-drain TACH inputs intended for fan speed measurement. Signal conditioning in the ADT7468 accommodates the slow rise and fall times typical of fan tachometer outputs. The maximum input signal range is 0 V to 5 V, even when VCC is less than 5 V. In the event that these inputs are supplied from fan outputs that exceed 0 V to 5 V, either resistive attenuation of the fan signal or diode clamping must be included to keep inputs within an acceptable range. Figure 42 to Figure 45 show circuits for most common fan TACH outputs. If the fan TACH output has a resistive pull-up to VCC, it can be connected directly to the fan input, as shown in Figure 42.
VCC 12V
Figure 40 shows a typical plot of the sensing waveform at the TACH/AIN pin.
PULL-UP 4.7k TYPICAL
TACH OUTPUT TACH
FAN SPEED COUNTER
ADT7468
04499-0-033
Figure 42. Fan with TACH Pull-Up to VCC
Figure 40. Fan Speed Sensing Waveform at TACH/AIN Pin
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ADT7468
If the fan output has a resistive pull-up to 12 V (or other voltage greater than 5 V) then the fan output can be clamped with a Zener diode, as shown in Figure 43. The Zener diode voltage should be chosen so that it is greater than VIH of the TACH input but less than 5 V, allowing for the voltage tolerance of the Zener. A value of between 3 V and 5 V is suitable.
12V VCC
Fan Speed Measurement
PULL-UP 4.7k TYPICAL
TACH OUTPUT
The fan counter does not count the fan TACH output pulses directly, because the fan speed could be less than 1,000 RPM and it would take several seconds to accumulate a reasonably large and accurate count. Instead, the period of the fan revolution is measured by gating an on-chip 90 kHz oscillator into the input of a 16-bit counter for N periods of the fan TACH output (Figure 46), so the accumulated count is actually proportional to the fan tachometer period and inversely proportional to the fan speed. N, the number of pulses counted, is determined by the settings of Register 0x7B (TACH pulses per revolution register). This register contains two bits for each fan, allowing one, two (default), three, or four TACH pulses to be counted.
TACH ZD1*
FAN SPEED COUNTER
04499-0-035
ADT7468
*CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8 x VCC
Figure 43. Fan with TACH Pull-Up to Voltage > 5 V, for example, 12 V) Clamped with Zener Diode
If the fan has a strong pull-up (less than 1 k) to 12 V or a totem-pole output, then a series resistor can be added to limit the Zener current, as shown in Figure 44.
5V OR 12V FAN PULL-UP TYP <1k OR TOTEM POLE VCC
CLOCK
PWM
TACH
1 2
TACH ZD1 ZENER*
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TACH OUTPUT
FAN SPEED COUNTER
3 4
ADT7468
Figure 46. Fan Speed Measurement
*CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8 x VCC
Figure 44. Fan with Strong TACH Pull-Up to > VCC or Totem-Pole Output, Clamped with Zener and Resistor
Fan Speed Measurement Registers
Alternatively, a resistive attenuator can be used, as shown in Figure 45. R1 and R2 should be chosen such that 2 V < VPULL-UP x R2/(RPULL-UP + R1 + R2) < 5 V The fan inputs have an input resistance of nominally 160 k to ground, which should be taken into account when calculating resistor values. With a pull-up voltage of 12 V and pull-up resistor less than 1 k, suitable values for R1 and R2 would be 100 k and 47 k, respectively. This gives a high input voltage of 3.83 V.
12V VCC
The fan tachometer readings are 16-bit values consisting of a 2-byte read from the ADT7468. Reg. 0x28, TACH1 Low Byte = 0x00 default Reg. 0x29, TACH1 High Byte = 0x00 default Reg. 0x2A, TACH2 Low Byte = 0x00 default Reg. 0x2B, TACH2 High Byte = 0x00 default Reg. 0x2C, TACH3 Low Byte = 0x00 default Reg. 0x2D, TACH3 High Byte = 0x00 default Reg. 0x2E, TACH4 Low Byte = 0x00 default Reg. 0x2F, TACH4 High Byte = 0x00 default
<1k R1* TACH OUTPUT TACH R2* FAN SPEED COUNTER
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ADT7468
Reading Fan Speed from the ADT7468
*SEE TEXT
Figure 45. Fan with Strong TACH Pull-Up to > VCC or Totem-Pole Output, Attenuated with R1/R2
The measurement of fan speeds involves a 2-register read for each measurement. The low byte should be read first. This causes the high byte to be frozen until both high and low byte registers have been read, preventing erroneous TACH readings. The fan tachometer reading registers report back the number of
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R1 10k
ADT7468
11.11 s period clocks (90 kHz oscillator) gated to the fan speed counter, from the rising edge of the first fan TACH pulse to the rising edge of the third fan TACH pulse (assuming two pulses per revolution are being counted). Because the device is essentially measuring the fan TACH period, the higher the count value, the slower the fan is actually running. A 16-bit fan tachometer reading of 0xFFFF indicates either that the fan has stalled or is running very slowly (<100 RPM).
High Limit: > Comparison Performed Calculating Fan Speed
Assuming a fan with a two pulses per revolution (and two pulses per revolution being measured), fan speed is calculated by Fan Speed (RPM) = (90,000 x 60)/Fan TACH Reading where Fan TACH Reading is the 16-bit fan tachometer reading.
Example:
Because the actual fan TACH period is being measured, falling below a fan TACH limit by 1 sets the appropriate status bit and can be used to generate an SMBALERT.
Fan TACH Limit Registers
TACH1 High Byte (Reg. 0x29) = 0x17 TACH1 Low Byte (Reg. 0x28) = 0xFF What is Fan 1 speed in RPM? Fan 1 TACH Reading = 0x17FF = 6143 (decimal) RPM = (f x 60)/Fan 1 TACH Reading RPM = (90000 x 60)/6143 Fan Speed = 879 RPM
Fan Pulses per Revolution
The fan TACH limit registers are 16-bit values consisting of two bytes. Reg. 0x54, TACH1 Minimum Low Byte = 0xFF default Reg. 0x55, TACH1 Minimum High Byte = 0xFF default Reg. 0x56, TACH2 Minimum Low Byte = 0xFF default Reg. 0x57, TACH2 Minimum High Byte = 0xFF default Reg. 0x58, TACH3 Minimum Low Byte = 0xFF default Reg. 0x59, TACH3 Minimum High Byte = 0xFF default Reg. 0x5A, TACH4 Minimum Low Byte = 0xFF default Reg. 0x5B, TACH4 Minimum High Byte = 0xFF default
Fan Speed Measurement Rate
Different fan models can output either 1, 2, 3, or 4 TACH pulses per revolution. Once the number of fan TACH pulses has been determined, it can be programmed into the fan pulses per revolution register (Reg. 0x7B) for each fan. Alternatively, this register can be used to determine the number or pulses per revolution output by a given fan. By plotting fan speed measurements at 100% speed with different pulses per revolution setting, the smoothest graph with the lowest ripple determines the correct pulses per revolution value.
Fan Pulses per Revolution Register <1:0> Fan 1 default = 2 pulses per revolution. <3:2> Fan 2 default = 2 pulses per revolution. <5:4> Fan 3 default = 2 pulses per revolution.
The fan TACH readings are normally updated once every second. The FAST bit (Bit 3) of Configuration Register 3 (Reg. 0x78), when set, updates the fan TACH readings every 250 ms. If any of the fans are not being driven by a PWM channel but are powered directly from 5 V or 12 V, their associated dc bit in Configuration Register 3 should be set. This allows TACH readings to be taken on a continuous basis for fans connected directly to a dc source. For optimal results, the associated dc bit should always be set when using 4-wire fans.
<7:6> Fan 4 default = 2 pulses per revolution.
00 = 1 pulse per revolution. 01 = 2 pulses per revolution. 10 = 3 pulses per revolution. 11 = 4 pulses per revolution.
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ADT7468
2-Wire Fan Speed Measurements (Low Frequency Mode Only)
The ADT7468 is capable of measuring the speed of 2-wire fans, that is, fans without TACH outputs. To do this, the fan must be interfaced as shown in the Driving 2-Wire Fans section. In this case, the TACH inputs should be reprogrammed as analog inputs, AIN.
Configuration Register 2 (Reg. 0x73) Bit 3 (AIN4) = 1, Pin 14 is reconfigured to measure the speed of a 2-wire fan using an external sensing resistor and coupling capacitor. Bit 2 (AIN3) = 1, Pin 9 is reconfigured to measure the speed of a 2-wire fan using an external sensing resistor and coupling capacitor. Bit 1 (AIN2) = 1, Pin 12 is reconfigured to measure the speed of a 2-wire fan using an external sensing resistor and coupling capacitor. Bit 0 (AIN1) = 1, Pin 11 is reconfigured to measure the speed of a 2-wire fan using an external sensing resistor and coupling capacitor. AIN Switching Threshold
Using Configuration Register 4 (0x40) Bit 5 (FSPDIS), this functionality can be changed (see the Disabling Fan Startup Timeout section).
PWM1 Configuration (Reg. 0x5C) <2:0> SPIN, startup timeout for PWM1.
000 = No startup timeout 001 = 100 ms 010 = 250 ms default 011 = 400 ms 100 = 667 ms 101 = 1 s 110 = 2 s 111 = 4 s PWM2 Configuration (Reg. 0x5D)
<2:0> SPIN, startup timeout for PWM2.
000 = No startup timeout 001 = 100 ms 010 = 250 ms default 011 = 400 ms 100 = 667 ms 101 = 1 s 110 = 2 s 111 = 4 s PWM3 Configuration (Reg. 0x5E)
<2:0> SPIN, start-up timeout for PWM3.
Having configured the TACH inputs as AIN inputs for 2-wire measurements, a user can select the sensing threshold for the AIN signal.
Configuration Register 4 (Reg. 0x7D) <3:2> AINL, input threshold for 2-wire fan speed measurements.
00 = 20 mV 01 = 40 mV 10 = 80 mV 11 = 130 mV Fan Spin-Up The ADT7468 has a unique fan spin-up function. It spins the fan at 100% PWM duty cycle until two TACH pulses are detected on the TACH input. Once two TACH pulses have been detected, the PWM duty cycle goes to the expected running value, for example, 33%. The advantage is that fans have different spin-up characteristics and take different times to overcome inertia. The ADT7468 runs the fans just fast enough to overcome inertia and is quieter on spin-up than fans programmed to spin up for a given spin-up time.
Fan Startup Timeout
000 = No startup timeout 001 = 100 ms 010 = 250 ms default 011 = 400 ms 100 = 667 ms 101 = 1 s 110 = 2 s 111 = 4 s Disabling Fan Startup Timeout Although fan startup makes fan spin-ups much quieter than fixed-time spin-ups, the option exists to use fixed spin-up times. Setting Bit 5 (FSPDIS) to 1 in Configuration Register 1 (Reg. 0x40) disables the spin-up for two TACH pulses. Instead, the fan spins up for the fixed time as selected in Reg. 0x5C to Reg. 0x5E.
To prevent the generation of false interrupts as a fan spins up (because it is below running speed), the ADT7468 includes a fan startup timeout function. During this time, the ADT7468 looks for two TACH pulses. If two TACH pulses are not detected, then an interrupt is generated.
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ADT7468
PWM Logic State
The PWM outputs can be programmed high for 100% duty cycle (noninverted) or low for 100% duty cycle (inverted).
PWM1 Configuration (Reg. 0x5C) <4> INV. 0 = Logic high for 100% PWM duty cycle. 1 = Logic low for 100% PWM duty cycle. PWM2 Configuration (Reg. 0x5D) <4> INV. 0 = Logic high for 100% PWM duty cycle. 1 = Logic low for 100% PWM duty cycle. PWM3 Configuration (Reg. 0x5E) <4> INV. 0 = Logic high for 100% PWM duty cycle. 1 = Logic low for 100% PWM duty cycle. Low Frequency Mode PWM Drive Frequency
In manual fan speed control mode, the ADT7468 allows the duty cycle of any PWM output to be manually adjusted. This can be useful, if the user wants to change fan speed in software or adjust PWM duty cycle output for test purposes. Bits <7:5> of Reg. 0x5C to Reg. 0x5E (PWM Configuration) control the behavior of each PWM output.
PWM Configuration Register (Reg. 0x5C to Reg. 0x5E) <7:5> BHVR.
111 = manual mode Once under manual control, each PWM output can be manually updated by writing to Reg. 0x30 to Reg. 0x32 (PWMx current duty cycle registers).
Programming the PWM Current Duty Cycle Registers
The PWM drive frequency can be adjusted for the application. Register 0x5F to Register 0x61 configure the PWM frequency for PWM1 to PWM3, respectively. In high frequency mode, the PWM drive frequency is always 22.5 kHz and cannot be changed.
PWM1 Frequency Registers (Reg. 0x5F to Reg. 0x61) <2:0> FREQ.
The PWM current duty cycle registers are 8-bit registers that allow the PWM duty cycle for each output to be set anywhere from 0% to 100% in steps of 0.39%. The value to be programmed into the PWMMIN register is given by Value (decimal) = PWMMIN/0.39
Example 1: For a PWM duty cycle of 50%,
Value (decimal) = 50/0.39 = 128 (decimal) Value = 128 (decimal) or 0x80 (hex)
Example 2: For a PWM duty cycle of 33%,
000 = 11.0 Hz 001 = 14.7 Hz 010 = 22.1 Hz 011 = 29.4 Hz 100 = 35.3 Hz default 101 = 44.1 Hz 110 = 58.8 Hz 111 = 88.2 Hz Fan Speed Control The ADT7468 controls fan speed using two modes: automatic and manual. In automatic fan speed control mode, fan speed is automatically varied with temperature and without CPU intervention, once initial parameters are set up. The advantage is that, if the system hangs, the user is guaranteed that the system is protected from overheating. The automatic fan speed control incorporates a feature called dynamic TMIN calibration. This feature reduces the design effort required to program the automatic fan speed control loop. See the Programming the Automatic Fan Speed Control Loop section.
Value (decimal) = 33/0.39 = 85 (decimal) Value = 85 (decimal) or 0x54 (hex)
PWM Duty Cycle Registers
Reg. 0x30 PWM1 Duty Cycle = 0x00 (0% default) Reg. 0x31 PWM2 Duty Cycle = 0x00 (0% default) Reg. 0x32 PWM3 Duty Cycle = 0x00 (0% default) By reading the PWMx current duty cycle registers, the user can keep track of the current duty cycle on each PWM output, even when the fans are running in automatic fan speed control mode or acoustic enhancement mode. See the Programming the Automatic Fan Speed Control Loop section for details.
OPERATING FROM 3.3 V STANDBY
The ADT7468 has been specifically designed to operate from a 3.3 V STBY supply. In computers that support S3 and S5 states, the core voltage of the processor is lowered in these states. If using the dynamic TMIN mode, lowering the core voltage of the processor changes the CPU temperature and changes the dynamics of the system under dynamic TMIN control. Likewise, when monitoring THERM, the THERM timer should be disabled during these states.
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ADT7468
Dynamic TMIN Control Register 1 (Reg. 0x36) <1> VCCPLO = 1
POWER-ON DEFAULT
When the ADT7468 is powered up, it polls the VCCP input. If VCCP stays below 0.75 V (the system CPU power rail is not powered up), then the ADT7468 assumes the functionality of the default registers after the ADT7468 is addressed via any valid SMBus transaction. If VCCP goes high (the system processor power rail is powered up), then a fail-safe timer begins to count down. If the ADT7468 is not addressed by any valid SMBus transaction before the failsafe timeout (4.6 s) lapses, then the ADT7468 drives the fans to full speed. If the ADT7468 is addressed by a valid SMBus transaction after this point, the fans stop, and the ADT7468 assumes its default settings and begins normal operation. If VCCP goes high (the system processor power rail is powered up), then a fail-safe timer begins to count down. If the ADT7468 has been addressed by a valid SMBus transaction before the failsafe timeout (4.6 s) lapsed, then the ADT7468 operates normally, assuming the functionality of all the default registers. See the flow chart in Figure 48.
ADT7468 IS POWERED UP
When the power is supplied from 3.3 V STBY and the VCCP voltage drops below the VCCP low limit, the following occurs: 1. 2. 3. 4. 5. Status Bit 1 (VCCP) in Status Register 1 is set. SMBALERT is generated, if enabled. THERM monitoring is disabled. The THERM timer should hold its value prior to the S3 or S5 state. Dynamic TMIN control is disabled. This prevents TMIN from being adjusted due to an S3 or S5 state. The ADT7468 is prevented from entering the shutdown state.
Once the core voltage, VCCP, goes above the VCCP low limit, everything is re-enabled and the system resumes normal operation.
XNOR TREE TEST MODE
The ADT7468 includes an XNOR tree test mode. This mode is useful for in-circuit test equipment at board-level testing. By applying stimulus to the pins included in the XNOR tree, it is possible to detect opens or shorts on the system board. The XNOR tree test is invoked by setting Bit 0 (XEN) of the XNOR tree test enable register (Reg. 0x6F). Figure 47 shows the signals that are exercised in the XNOR tree test mode.
VID0 VID1
Y
HAS THE ADT7468 BEEN ACCESSED BY A VALID SMBUS TRANSACTION? N IS VCCP ABOVE 0.75V? N Y START FAIL-SAFE TIMER CHECK VCCP
VID2
Y
VID3
HAS THE ADT7468 BEEN ACCESSED BY A VALID SMBUS TRANSACTION? N FAIL-SAFE TIMER ELAPSES AFTER THE FAIL-SAFE TIMEOUT
VID4
TACH1
HAS THE ADT7468 BEEN ACCESSED BY A VALID SMBUS TRANSACTION? Y
RUN THE FANS TO FULL SPEED N
TACH2
TACH3
HAS THE ADT7468 BEEN ACCESSED BY A VALID SMBUS TRANSACTION? Y
N
TACH4
START UP THE ADT7468 NORMALLY
SWITCH OFF FANS
PWM2
04499-0-040
Figure 48. Power-On Flow Chart
PWM3
PWM1/XTO
Figure 47. XNOR Tree Test
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ADT7468 PROGRAMMING THE AUTOMATIC FAN SPEED CONTROL LOOP
Note: To more efficiently understand the automatic fan speed control loop, it is strongly recommended to use the ADT7468 evaluation board and software while reading this section. This section provides the system designer with an understanding of the automatic fan control loop, and provides step-by-step guidance on effectively evaluating and selecting critical system parameters. To optimize the system characteristics, the designer needs to give some thought to system configuration, including the number of fans, where they are located, and what temperatures are being measured in the particular system. The mechanical or thermal engineer who is tasked with the system thermal characterization should also be involved at the beginning of the process. current consumption. The automatic fan speed control mode is very flexible owing to the number of programmable parameters, including TMIN and TRANGE. The TMIN and TRANGE values for a temperature channel and, therefore, for a given fan are critical, because they define the thermal characteristics of the system. The thermal validation of the system is one of the most important steps in the design process, so these values should be selected carefully. Figure 49 gives a top-level overview of the automatic fan control circuitry on the ADT7468. From a systems-level perspective, up to three system temperatures can be monitored and used to control three PWM outputs. The three PWM outputs can be used to control up to four fans. The ADT7468 allows the speed of four fans to be monitored. Each temperature channel has a thermal calibration block, allowing the designer to individually configure the thermal characteristics of each temperature channel. For example, one can decide to run the CPU fan when CPU temperature increases above 60C and a chassis fan when the local temperature increases above 45C. At this stage, the designer has not assigned these thermal calibration settings to a particular fan drive (PWM) channel. The right side of Figure 49 shows controls that are fan-specific. The designer has individual control over parameters such as minimum PWM duty cycle, fan speed failure thresholds, and even ramp control of the PWM outputs. Automatic fan control, then, ultimately allows graceful fan speed changes that are less perceptible to the system user.
AUTOMATIC FAN CONTROL OVERVIEW
The ADT7468 can automatically control the speed of fans based upon the measured temperature. This is done independently of CPU intervention once initial parameters are set up. The ADT7468 has a local temperature sensor and two remote temperature channels that can be connected to a CPU on-chip thermal diode (available on Intel Pentium class and other CPUs). These three temperature channels can be used as the basis for automatic fan speed control to drive fans using pulsewidth modulation (PWM). Automatic fan speed control reduces acoustic noise by optimizing fan speed according to accurately measured temperature. Reducing fan speed can also decrease system
THERMAL CALIBRATION
100%
PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT)
PWM CONFIG
PWM GENERATOR
PWM1
REMOTE 1 TEMP
TMIN
TRANGE
0% PWM MIN TACHOMETER 1 MEASUREMENT TACH1 PWM CONFIG
THERMAL CALIBRATION
100%
MUX
0% PWM MIN
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 2 MEASUREMENT
PWM GENERATOR
PWM2
LOCAL TEMP
TMIN
TRANGE
TACH2 PWM CONFIG
THERMAL CALIBRATION
100%
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 3 AND 4 MEASUREMENT
PWM GENERATOR
PWM3
REMOTE 2 TEMP
TMIN
TRANGE
0%
Figure 49. Automatic Fan Control Block Diagram
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TACH3
ADT7468
STEP 1: HARDWARE CONFIGURATION
During system design, the motherboard sensing and control capabilities should be addressed early in the design stages. Decisions about how these capabilities are used should involve the system thermal/mechanical engineer. Ask the following questions: 1. What ADT7468 functionality will be used? * * * * PWM2 or SMBALERT? TACH4 fan speed measurement or overtemperature THERM function? 5 V voltage monitoring or overtemperature THERM function? 12 V voltage monitoring or VID5 input? 4. 2. How many fans will be supported in system, three or four? This influences the choice of whether to use the TACH4 pin or to reconfigure it for the THERM function. Is the CPU fan to be controlled using the ADT7468 or will it run at full speed 100% of the time? If run at 100%, this frees up a PWM output, but the system is louder. Where will the ADT7468 be physically located in the system? This influences the assignment of the temperature measurement channels to particular system thermal zones. For example, locating the ADT7468 close to the VRM controller circuitry allows the VRM temperature to be monitored using the local temperature channel.
3.
The ADT7468 offers multifunctional pins that can be reconfigured to suit different system requirements and physical layouts. These multifunction pins are software programmable.
THERMAL CALIBRATION
100%
PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT)
PWM CONFIG
PWM GENERATOR
PWM1
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0% PWM MIN TACHOMETER 1 MEASUREMENT TACH1 PWM CONFIG CPU FAN SINK
THERMAL CALIBRATION
100%
MUX
0% PWM MIN
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 2 MEASUREMENT
PWM GENERATOR
PWM2
TMIN LOCAL = VRM TEMP
TRANGE
TACH2 PWM CONFIG FRONT CHASSIS PWM GENERATOR PWM3
THERMAL CALIBRATION
100%
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 3 AND 4 MEASUREMENT
TMIN REMOTE 2 = CPU TEMP
TRANGE
0%
TACH3
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REAR CHASSIS
Figure 50. Hardware Configuration Example
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ADT7468
RECOMMENDED IMPLEMENTATION 1
Configuring the ADT7468 as in Figure 51 provides the system designer with the following features: 1. 2. 3. 4. 5. 6. Six VID inputs (VID0 to VID5) for VRM10 support. Two PWM outputs for fan control of up to three fans. (The front and rear chassis fans are connected in parallel.) Three TACH fan speed measurement inputs. VCC measured internally through Pin 4. CPU core voltage measurement (VCORE). 2.5 V measurement input used to monitor CPU current (connected to VCOMP output of ADP316x VRM controller). This is used to determine CPU power consumption. 7. 8. 9. 5 V measurement input. VRM temperature using local temperature sensor. CPU temperature measured using the Remote 1 temperature channel.
10. Ambient temperature measured through the Remote 2 temperature channel. 11. If not using VID5, this pin can be reconfigured as the 12 V monitoring input. 12. Bidirectional THERM pin allows the monitoring of PROCHOT output from an Intel P4 processor, for example, or can be used as an overtemperature THERM output. 13. SMBALERT system interrupt output.
FRONT CHASSIS FAN
TACH2 PWM1 TACH1
CPU FAN
REAR CHASSIS FAN
PWM3 VID[0:4]/VID[0.5] TACH3 D2+ D2- THERM
5(VRM9)/6(VRM10)
PROCHOT CPU AMBIENT TEMPERATURE D1+ D1-
ADT7468
3.3VSB 5V 12V/VID5 SDA SCL ADP316x VRM CONTROLLER VCOMP CURRENT VCORE GND ICH SMBALERT
04499-0-056
Figure 51. Recommended Implementation 1
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ADT7468
RECOMMENDED IMPLEMENTATION 2
Configuring the ADT7468 as in Figure 52 provides the system designer with the following features: 1. 2. 3. 4. 5. 6. Six VID inputs (VID0 to VID5) for VRM10 support. Three PWM outputs for fan control of up to three fans. (All three fans can be individually controlled.) Three TACH fan speed measurement inputs. VCC measured internally through Pin 4. CPU core voltage measurement (VCORE). 2.5 V measurement input used to monitor CPU current (connected to VCOMP output of ADP316x VRM controller). This is used to determine CPU power consumption. 7. 8. 9. 5 V measurement input. VRM temperature using local temperature sensor. CPU temperature measured using the Remote 1 temperature channel.
10. Ambient temperature measured through the Remote 2 temperature channel. 11. If not using VID5, this pin can be reconfigured as the 12 V monitoring input. 12. Bidirectional THERM pin allows the monitoring of PROCHOT output from an Intel P4 processor, for example, or can be used as an overtemperature THERM output.
FRONT CHASSIS FAN
TACH2 PWM1 TACH1
CPU FAN
REAR CHASSIS FAN
PWM3 VID[0:4]/VID[0.5] TACH3 D2+ D2- THERM
5(VRM9)/6(VRM10)
PROCHOT AMBIENT TEMPERATURE D1+ D1-
CPU
ADT7468
3.3VSB 5V 12V/VID5 SDA SCL ADP316x VRM CONTROLLER VCOMP CURRENT GND
04499-0-057
VCORE
ICH
Figure 52. Recommended Implementation 2
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ADT7468
STEP 2: CONFIGURING THE MUX
After the system hardware configuration is determined, the fans can be assigned to particular temperature channels. Not only can fans be assigned to individual channels, but the behavior of the fans is also configurable. For example, fans can be run under automatic fan control, can be run manually (under software control), or can be run at the fastest speed calculated by multiple temperature channels. The MUX is the bridge between temperature measurement channels and the three PWM outputs.
Bits <7:5> (BHVR) of Registers 0x5C, 0x5D, and 0x5E (PWM configuration registers) control the behavior of the fans connected to the PWM1, PWM2, and PWM3 outputs. The values selected for these bits determine how the MUX connects a temperature measurement channel to a PWM output. Automatic Fan Control MUX Options <7:5> (BHVR), Registers 0x5C, 0x5D, 0x5E.
101 = Fastest speed calculated by local and Remote 2 temperature controls PWMx 110 = Fastest speed calculated by all three temperature channels controls PWMx The Fastest Speed Calculated options pertain to controlling one PWM output based on multiple temperature channels. The thermal characteristics of the three temperature zones can be set to drive a single fan. An example would be the fan turning on when Remote 1 temperature exceeds 60C or if the local temperature exceeds 45C.
Other MUX Options <7:5> (BHVR), Registers 0x5C, 0x5D, 0x5E.
011 = PWMx runs full speed 100 = PWMx disabled (default) 111 = manual mode. PWMx is runner under software control. In this mode, PWM duty cycle registers (Registers 0x30 to 0x32) are writable and control the PWM outputs.
000 = Remote 1 temperature controls PWMx 001 = local temperature controls PWMx 010 = Remote 2 temperature controls PWMx
MUX
THERMAL CALIBRATION
100%
PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT)
PWM CONFIG
PWM GENERATOR
PWM1
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0% PWM MIN TACHOMETER 1 MEASUREMENT TACH1 PWM CONFIG CPU FAN SINK
THERMAL CALIBRATION
100%
MUX
0% PWM MIN
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 2 MEASUREMENT
PWM GENERATOR
PWM2
TMIN LOCAL = VRM TEMP
TRANGE
TACH2 PWM CONFIG FRONT CHASSIS PWM GENERATOR PWM3
THERMAL CALIBRATION
100%
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 3 AND 4 MEASUREMENT
TMIN REMOTE 2 = CPU TEMP
TRANGE
0%
TACH3
04499-0-058
REAR CHASSIS
Figure 53. Assigning Temperature Channels to Fan Channels
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ADT7468
MUX Configuration Example Example MUX Settings <7:5> (BHVR), PWM1 Configuration Register 0x5C.
This is an example of how to configure the MUX in a system using the ADT7468 to control three fans. The CPU fan sink is controlled by PWM1, the front chassis fan is controlled by PWM2, and the rear chassis fan is controlled by PWM3. The MUX is configured for the following fan control behavior: * PWM1 (CPU fan sink) is controlled by the fastest speed calculated by the local (VRM temperature) and Remote 2 (processor) temperature. In this case, the CPU fan sink is also being used to cool the VRM. PWM2 (front chassis fan) is controlled by the Remote 1 temperature (ambient). PWM3 (rear chassis fan) is controlled by the Remote 1 temperature (ambient).
101 = Fastest speed calculated by local and Remote 2 temperature controls PWM1
<7:5> (BHVR), PWM2 Configuration Register 0x5D.
000 = Remote 1 temperature controls PWM2
<7:5> (BHVR), PWM3 Configuration Register 0x5E.
000 = Remote 1 temperature controls PWM3 These settings configure the MUX, as shown in Figure 54.
* *
THERMAL CALIBRATION
100%
PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT)
PWM CONFIG
PWM GENERATOR
PWM1
TMIN REMOTE 2 = CPU TEMP
TRANGE
0%
THERMAL CALIBRATION
MUX
100%
PWM MIN
TACHOMETER 1 MEASUREMENT
TACH1 PWM CONFIG CPU FAN SINK
RAMP CONTROL (ACOUSTIC ENHANCEMENT) 0% PWM MIN TACHOMETER 2 MEASUREMENT
PWM GENERATOR
PWM2
TMIN LOCAL = VRM TEMP
TRANGE
TACH2 PWM CONFIG FRONT CHASSIS PWM GENERATOR PWM3
THERMAL CALIBRATION
100%
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 3 AND 4 MEASUREMENT
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0%
TACH3
04499-0-059
REAR CHASSIS
Figure 54. MUX Configuration Example
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ADT7468
STEP 3: TMIN SETTINGS FOR THERMAL CALIBRATION CHANNELS
TMIN is the temperature at which the fans start to turn on under automatic fan control. The speed at which the fan runs at TMIN is programmed later. The TMIN values chosen are temperature channel specific, for example, 25C for ambient channel, 30C for VRM temperature, and 40C for processor temperature. TMIN is an 8-bit value, either twos complement or Offset 64, that can be programmed in 1C increments. There is a TMIN register associated with each temperature measurement channel: Remote 1 Local, and Remote 2 Temp. Once the TMIN value is exceeded, the fan turns on and runs at the minimum PWM duty cycle. The fan turns off once the temperature has dropped below TMIN - THYST. To overcome fan inertia, the fan is spun up until two valid TACH rising edges are counted. See the Fan Startup Timeout section for more details. In some cases, primarily for psychoacoustic reasons, it is desirable that the fan never switch off below TMIN. Bits <7:5> of Enhanced Acoustics Register 1 (Reg. 0x62), when set, keep the fans running at the PWM minimum duty cycle, if the temperature should fall below TMIN.
TMIN Registers
Reg. 0x67, Remote 1 Temperature TMIN = 0x9A (90C) Reg. 0x68, Local Temperature TMIN = 0x9A (90C) Reg. 0x69, Remote 2 Temperature TMIN = 0x9A (90C)
Enhance Acoustics Register 1 (Reg. 0x62) Bit 7 (MIN3) = 0, PWM3 is off (0% PWM duty cycle) when temperature is below TMIN - THYST. Bit 7 (MIN3) = 1, PWM3 runs at PWM3 minimum duty cycle below TMIN - THYST. Bit 6 (MIN2) = 0, PWM2 is off (0% PWM duty cycle) when temperature is below TMIN - THYST. Bit 6 (MIN2) = 1, PWM2 runs at PWM2 minimum duty cycle below TMIN - THYST. Bit 5 (MIN1) = 0, PWM1 is off (0% PWM duty cycle) when temperature is below TMIN - THYST. Bit 5 (MIN1) = 1, PWM1 runs at PWM1 minimum duty cycle below TMIN - THYST.
100%
PWM DUTYCYCLE
0% TMIN
THERMAL CALIBRATION
100%
PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT)
PWM CONFIG
PWM GENERATOR
PWM1
TMIN REMOTE 2 = CPU TEMP
TRANGE
0% PWM MIN TACHOMETER 1 MEASUREMENT TACH1 PWM CONFIG CPU FAN SINK
THERMAL CALIBRATION
100%
MUX
0% PWM MIN
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 2 MEASUREMENT
PWM GENERATOR
PWM2
TMIN LOCAL = VRM TEMP
TRANGE
TACH2 PWM CONFIG FRONT CHASSIS PWM GENERATOR PWM3
THERMAL CALIBRATION
100%
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 3 AND 4 MEASUREMENT
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0%
TACH3
04499-0-060
REAR CHASSIS
Figure 55. Understanding the TMIN Parameter
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ADT7468
STEP 4: PWMMIN FOR EACH PWM (FAN) OUTPUT
PWMMIN is the minimum PWM duty cycle at which each fan in the system runs. It is also the start speed for each fan under automatic fan control once the temperature rises above TMIN. For maximum system acoustic benefit, PWMMIN should be as low as possible. Depending on the fan used, the PWMMIN setting is usually in the 20% to 33% duty cycle range. This value can be found through fan validation.
100%
PWM DUTY CYCLE
Programming the PWMMIN Registers
The PWMMIN registers are 8-bit registers that allow the minimum PWM duty cycle for each output to be configured anywhere from 0% to 100%. This allows the minimum PWM duty cycle to be set in steps of 0.39%. The value to be programmed into the PWMMIN register is given by Value (decimal) = PWMMIN/0.39
Example 1: For a minimum PWM duty cycle of 50%,
Value (decimal) = 50/0.39 = 128 (decimal) Value = 128 (decimal) or 80 (hex)
Example 2: For a minimum PWM duty cycle of 33%,
PWMMIN 0%
04499-0-061
Value (decimal) = 33/0.39 = 85 (decimal) Value = 85 (decimal)l or 54 (hex)
PWMMIN Registers
TMIN
TEMPERATURE
Figure 56. PWMMIN Determines Minimum PWM Duty Cycle
More than one PWM output can be controlled from a single temperature measurement channel. For example, Remote 1 temperature can control PWM1 and PWM2 outputs. If two different fans are used on PWM1 and PWM2, then the fan characteristics can be set up differently. As a result, Fan 1 driven by PWM1 can have a different PWMMIN value than that of Fan 2 connected to PWM2. Figure 57 illustrates this as PWM1MIN (front fan) is turned on at a minimum duty cycle of 20%, while PWM2MIN (rear fan) turns on at a minimum of 40% duty cycle. Note, however, that both fans turn on at exactly the same temperature, defined by TMIN.
100%
Reg. 0x64, PWM1 Minimum Duty Cycle = 0x80 (50% default) Reg. 0x65 PWM2 Minimum Duty Cycle = 0x80 (50% default) Reg. 0x66, PWM3 Minimum Duty Cycle = 0x80 (50% default)
Note on Fan Speed and PWM Duty Cycle
The PWM duty cycle does not directly correlate to fan speed in RPM. Running a fan at 33% PWM duty cycle does not equate to running the fan at 33% speed. Driving a fan at 33% PWM duty cycle actually runs the fan at closer to 50% of its full speed. This is because fan speed in %RPM generally relates to the square root of PWM duty cycle. Given a PWM square wave as the drive signal, fan speed in RPM approximates to
% fanspeed = PWM duty cycle x 10
STEP 5: PWMMAX FOR PWM (FAN) OUTPUTS
M2 PW M1 PW
PWM2MIN PWM1MIN 0%
TMIN
TEMPERATURE
04499-0-062
PWMMAX is the maximum duty cycle that each fan in the system runs at under the automatic fan speed control loop. For maximum system acoustic benefit, PWMMAX should be as low as possible, but should be capable of maintaining the processor temperature limit at an acceptable level. If the THERM temperature limit is exceeded, the fans are still boosted to 100% for fail-safe cooling. There is a PWMMAX limit for each fan channel. The default value of this register is 0xFF and so has no effect unless it is programmed.
Figure 57. Operating Two Different Fans from a Single Temperature Channel
PWM DUTY CYCLE
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ADT7468
STEP 6: TRANGE FOR TEMPERATURE CHANNELS
100% PWMMAX
PWMMIN 0%
04499-0-063
TRANGE is the range of temperature over which automatic fan control occurs once the programmed TMIN temperature has been exceeded. TRANGE is a temperature slope, not an arbitrary value, that is, a TRANGE of 40C holds true only for PWMMIN = 33%. If PWMMIN is increased or decreased, the effective TRANGE changes.
TRANGE 100%
PWM DUTY CYCLE
PWM DUTY CYCLE
TMIN
TEMPERATURE
Figure 58. PWMMAX Determines Maximum PWM Duty Cycle below the THERM Temperature Limit
Programming the PWMMAX Registers
TMIN
TEMPERATURE
The value to be programmed into the PWMMAX register is given by Value (decimal) = PWMMAX/0.39
Example 1: For a maximum PWM duty cycle of 50%,
Figure 59. TRANGE Parameter Affects Cooling Slope
The TRANGE or fan control slope is determined by the following procedure: 1. 2. Determine the maximum operating temperature for that channel (for example, 70C). Determine experimentally the fan speed (PWM duty cycle value) that does not exceed the temperature at the worstcase operating points. (For example, 70C is reached when the fans are running at 50% PWM duty cycle.) Determine the slope of the required control loop to meet these requirements. Using the ADT7468 evaluation software, you can graphically program and visualize this functionality. Ask your local Analog Devices representative for details.
100%
PWM DUTY CYCLE
Value (decimal) - 50/0.39 = 128 (decimal) Value = 128 (decimal) or 80 (hex)
Example 2: For a minimum PWM duty cycle of 75%,
Value (decimal) = 75/0.39 = 85 (decimal) Value = 192 (decimal) or C0 (hex)
PWMMAX Registers
3. 4.
Reg. 0x38, PWM1 Maximum Duty Cycle = 0xFF (100% default) Reg. 0x39, PWM2 Maximum Duty Cycle = 0xFF (100% default) Reg. 0x3A, PWM3 Maximum Duty Cycle = 0xFF (100% default) See the Note on Fan Speed and PWM Duty Cycle on Page 43.
50% 33% 0%
04499-0-065
30C 40C TMIN
Figure 60. Adjusting PWMMIN Affects TRANGE
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04499-0-064
The PWMMAX registers are 8-bit registers that allow the maximum PWM duty cycle for each output to be configured anywhere from 0% to 100%. This allows the maximum PWM duty cycle to be set in steps of 0.39%.
PWMMIN 0%
ADT7468
TRANGE is implemented as a slope, which means that as PWMMIN is changed, TRANGE changes, but the actual slope remains the same. The higher the PWMMIN value, the smaller the effective TRANGE, that is, the fan reaches full speed (100%) at a lower temperature.
Example: Calculate TMAX, given that TMIN = 30C, TRANGE = 40C, and PWMMIN = 33% duty cycle = 85 (decimal).
100%
PWM DUTY CYCLE
TMAX = TMIN + (Max DC - Min DC) x TRANGE /170 TMAX = 30C + (100% - 33%) x 40C/170 TMAX = 30C + (255 - 85) x 40C/170 TMAX = 70C (effective TRANGE = 40C)
Example: Calculate TMAX, given that TMIN = 30C, TRANGE = 40C, and PWMMIN = 50% duty cycle = 128 (decimal).
50% 33% 25% 10% 0% 30C
04499-0-066
TMAX = TMIN + (Max DC - Min DC) x TRANGE /170 TMAX = 30C + (100% - 50%) x 40C/170 TMAX = 30C + (255 - 128) x 40C/170 TMAX = 60C (effective TRANGE = 30C)
Selecting a TRANGE Slope
40C 45C 54C TMIN
The TRANGE value can be selected for each temperature channel: Remote 1, local, and Remote 2 temperature. Bits <7:4> (TRANGE) of Registers 0x5F to 0x61 define the TRANGE value for each temperature channel.
Table 13. Selecting a TRANGE Value
Bits <7:4>1 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111
1
Figure 61. Increasing PWMMIN Changes Effective TRANGE
For a given TRANGE value, the temperature at which the fan runs at full speed for different PWMMIN values can be easily calculated: TMAX = TMIN + (Max DC - Min DC) x TRANGE /170 where: TMAX is the temperature at which the fan runs full speed. TMIN is the temperature at which the fan turns on. Max DC is the maximum duty cycle (100%) = 255 decimal. Min DC is equal to PWMMIN. TRANGE is the duty PWM duty cycle vs. temperature slope.
Example: Calculate T, given that TMIN = 30C, TRANGE = 40C, and PWMMIN = 10% duty cycle = 26 (decimal).
TMAX = TMIN + (Max DC - Min DC) x TRANGE /170 TMAX = 30C + (100% - 10%) x 40C/170 TMAX = 30C + (255 - 26) x 40C/170 TMAX = 84C (effective TRANGE = 54C)
Example: Calculate TMAX, given that TMIN = 30C, TRANGE = 40C, and PWMMIN = 25% duty cycle = 64 (decimal).
TRANGE (C) 2 2.5 3.33 4 5 6.67 8 10 13.33 16 20 26.67 32 (default) 40 53.33 80
Register 0x5F configures Remote 1 TRANGE. Register 0x60 configures Local TRANGE. Register 0x61 configures Remote 2 TRANGE.
Summary of TRANGE Function
TMAX = TMIN + (Max DC - Min DC) x TRANGE /170 TMAX = 30C + (100% - 25%) x 40C/170 TMAX = 30C + (255 - 64) x 40C/170 TMAX = 75C (effective TRANGE = 45C)
When using the automatic fan control function, the temperature at which the fan reaches full speed can be calculated by TMAX = TMIN + TRANGE Equation 1 holds true only when PWMMIN is equal to 33% PWM duty cycle. (1)
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ADT7468
Increasing or decreasing PWMMIN changes the effective TRANGE, although the fan control still follows the same PWM duty cycle to temperature slope. The effective TRANGE for different PWMMIN values can be calculated using Equation 2: TMAX = TMIN + (Max DC - Min DC) x TRANGE/170 where: (Max DC - Min DC) x TRANGE/170 is the effective TRANGE value. See the Note on Fan Speed and PWM Duty Cycle. Figure 62 shows PWM duty cycle versus temperature for each TRANGE setting. The lower graph shows how each TRANGE setting affects fan speed versus temperature. As can be seen from the graph, the effect on fan speed is nonlinear.
100 90 80
PWM DUTY CYCLE (%)
100 90 80
PWM DUTY CYCLE (%)
2C 2.5C 3.33C 4C 5C 6.67C 8C 10C 13.3C 16C 20C 26.6C 32C 40C 53.3C 20 40 60 80 TEMPERATURE ABOVE TMIN 100 120 80C
70 60 50 40 30 20 10 0 0
(2)
100 90 80
FAN SPEED (% OF MAX)
2C 2.5C 3.33C 4C 5C 6.67C 8C 10C 13.3C 16C 20C 26.6C 32C 40C 80C
04499-0-068
2C 2.5C 3.33C 4C 5C 6.67C 8C 10C 13.3C 16C 20C 26.6C 32C 40C 53.3C 20 40 60 80 TEMPERATURE ABOVE TMIN 100 120 80C
70 60 50 40 30 20 10 0 0 20 40 60 80 TEMPERATURE ABOVE TMIN 100 120
70 60 50 40 30 20 10 0 0
53.3C
Figure 63. TRANGE and % Fan Speed Slopes with PWMMIN = 20%
2C 2.5C 3.33C 4C 5C 6.67C 8C 10C 13.3C 16C 20C 26.6C 32C 40C 80C
04499-0-067
100 90 80
FAN SPEED (% OF MAX)
Example: Determining TRANGE for Each Temperature Channel
70 60 50 40 30 20 10 0 0 20 40 60 80 TEMPERATURE ABOVE TMIN 100 120
The following example shows how the different TMIN and TRANGE settings can be applied to three different thermal zones. In this example, the following TRANGE values apply: TRANGE = 80C for ambient temperature TRANGE = 53.3C for CPU temperature TRANGE = 40C for VRM temperature This example uses the MUX configuration described in Step 2, with the ADT7468 connected as shown in Figure 54. Both CPU temperature and VRM temperature drive the CPU fan connected to PWM1. Ambient temperature drives the front chassis fan and rear chassis fan connected to PWM2 and PWM3. The front chassis fan is configured to run at PWMMIN = 20%. The rear chassis fan is configured to run at PWMMIN = 30%. The CPU fan is configured to run at PWMMIN = 10%.
Note on 4-Wire Fans
53.3C
Figure 62. TRANGE vs. Actual Fan Speed Profile
The graphs in Figure 62 assume that the fan starts from 0% PWM duty cycle. Clearly, the minimum PWM duty cycle, PWMMIN, needs to be factored in to see how the loop actually performs in the system. Figure 63 shows how TRANGE is affected when the PWMMIN value is set to 20%. It can be seen that the fan actually runs at about 45% fan speed when the temperature exceeds TMIN.
The control range for 4-wire fans is much wider than that of 2-wire or 3-wire fans. In many cases, 4-wire fans can start with a PWM drive of as little as 20%.
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ADT7468
100 90 80
PWM DUTY CYCLE (%)
The fans remain running at 100% until the temperature drops below TTHERM minus hysteresis, where hysteresis is the number programmed into the Hysteresis Registers 0x6D and 0x6E. The default hysteresis value is 4C. The TTHERM limit should be considered the maximum worst-case operating temperature of the system. Because exceeding any TTHERM limit runs all fans at 100%, it has very negative acoustic effects. Ultimately, this limit should be set up as a fail-safe, and one should ensure that it is not exceeded under normal system operating conditions.
10 20 30 40 50 60 70 80 90 100 TEMPERATURE ABOVE TMIN
70 60 50 40 30 20 10 0 0
Note that the TTHERM limits are nonmaskable and affect the fan speed no matter how automatic fan control settings are configured. This allows some flexibility, because a TRANGE value can be selected based on its slope, while a hard limit (such as 70C), can be programmed as TMAX (the temperature at which the fan reaches full speed) by setting TTHERM to that limit (for example, 70C).
THERM Registers
100 90 80
FAN SPEED (% MAX RPM)
70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100
04499-0-069
Reg. 0x6A, Remote 1 THERM limit = 0xA4 (100C default) Reg. 0x6B, Local THERM limit = 0xA4 (100C default) Reg. 0x6C, Remote 2 THERM limit = 0xA4 (100C default)
Hysteresis Registers
TEMPERATURE ABOVE TMIN
Reg. 0x6D, Remote 1, Local Hysteresis Register
<7:4>, Remote 1 temperature hysteresis (4C default). <3:0>, Local temperature hysteresis (4C default).
Figure 64. TRANGE and % Fan Speed Slopes for VRM, Ambient, and CPU Temperature Channels
STEP 7: TTHERM FOR TEMPERATURE CHANNELS
TTHERM is the absolute maximum temperature allowed on a temperature channel. Above this temperature, a component such as the CPU or VRM might be operating beyond its safe operating limit. When the temperature measured exceeds TTHERM, all fans are driven at 100% PWM duty cycle (full speed) to provide critical system cooling.
Reg. 0x6E, Remote 2 Temperature Hysteresis Register
<7:4>, Remote 2 temperature hysteresis (4C default).
Because each hysteresis setting is four bits, hysteresis values are programmable from 1C to 15C. It is not recommended that hysteresis values ever be programmed to 0C, because this disables hysteresis. In effect, this would cause the fans to cycle between normal speed and 100% speed, creating unsettling acoustic noise.
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ADT7468
TRANGE 100%
PWM DUTYCYCLE
0%
TMIN
T THERM
THERMAL CALIBRATION
100%
PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT)
PWM CONFIG
PWM GENERATOR
PWM1
TMIN REMOTE 2 = CPU TEMP
TRANGE
0% PWM MIN TACHOMETER 1 MEASUREMENT TACH1 PWM CONFIG CPU FAN SINK
THERMAL CALIBRATION
100%
MUX
0% PWM MIN
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 2 MEASUREMENT
PWM GENERATOR
PWM2
TMIN LOCAL = VRM TEMP
TRANGE
TACH2 PWM CONFIG FRONT CHASSIS PWM GENERATOR PWM3
THERMAL CALIBRATION
100%
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 3 AND 4 MEASUREMENT
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0%
TACH3
04499-0-070
REAR CHASSIS
Figure 65. How TTHERM Relates to Automatic Fan Control
STEP 8: THYST FOR TEMPERATURE CHANNELS
THYST is the amount of extra cooling a fan provides after the temperature measured has dropped back below TMIN before the fan turns off. The premise for temperature hysteresis (THYST) is that, without it, the fan would merely chatter or cycle on and off regularly whenever temperature is hovering at about the TMIN setting. The THYST value chosen determines the amount of time needed for the system to cool down or heat up as the fan is turning on and off. Values of hysteresis are programmable in the range 1C to 15C. Larger values of THYST prevent the fans from chattering on and off. The THYST default value is set at 4C. The THYST setting applies not only to the temperature hysteresis for fan on/off, but the same setting is used for the TTHERM hysteresis value, described in Step 6. Therefore, programming Registers 0x6D and 0x6E sets the hysteresis for both fan on/off and the THERM function.
Hysteresis Registers
Reg. 0x6D, Remote 1, Local Hysteresis Register
<7:4>, Remote 1 temperature hysteresis (4C default). <3:0>, local temperature hysteresis (4C default).
Reg. 0x6E, Remote 2 Temp Hysteresis Register
<7:4>, Remote 2 temperature hysteresis (4C default).
In some applications, it is required that fans not turn off below TMIN, but remain running at PWMMIN. Bits <7:5> of Enhanced Acoustics Register 1 (Reg. 0x62) allow the fans to be turned off or to be kept spinning below TMIN. If the fans are always on, the THYST value has no effect on the fan when the temperature drops below TMIN.
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ADT7468
TRANGE 100%
PWM DUTYCYCLE
0%
TMIN
T THERM
THERMAL CALIBRATION
100%
PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT)
PWM CONFIG
PWM GENERATOR
PWM1
TMIN REMOTE 2 = CPU TEMP
TRANGE
0% PWM MIN TACHOMETER 1 MEASUREMENT TACH1 PWM CONFIG CPU FAN SINK
THERMAL CALIBRATION
100%
MUX
0% PWM MIN
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 2 MEASUREMENT
PWM GENERATOR
PWM2
TMIN LOCAL = VRM TEMP
TRANGE
TACH2 PWM CONFIG FRONT CHASSIS PWM GENERATOR PWM3
THERMAL CALIBRATION
100%
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 3 AND 4 MEASUREMENT
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0%
TACH3
04499-0-071
REAR CHASSIS
Figure 66. The THYST Value Applies to Fan On/Off Hysteresis and THERM Hysteresis
Enhance Acoustics Register 1 (Reg. 0x62) Bit 7 (MIN3) = 0, PWM3 is off (0% PWM duty cycle) when temperature is below TMIN - THYST. Bit 7 (MIN3) = 1, PWM3 runs at PWM3 minimum duty cycle below TMIN - THYST. Bit 6 (MIN2) = 0, PWM2 is off (0% PWM duty cycle) when temperature is below TMIN - THYST. Bit 6 (MIN2) = 1, PWM2 runs at PWM2 minimum duty cycle below TMIN - THYST. Bit 5 (MIN1) = 0, PWM1 is off (0% PWM duty cycle) when temperature is below TMIN - THYST. Bit 5 (MIN1) = 1, PWM1 runs at PWM1 minimum duty cycle below TMIN - THYST.
DYNAMIC TMIN CONTROL MODE
In addition to the automatic fan speed control mode described in the Automatic Fan Control Overview section, the ADT7468 has a mode that extends the basic automatic fan speed control loop. Dynamic TMIN control allows the ADT7468 to intelligently adapt the system's cooling solution for best system performance or lowest possible system acoustics, depending on user or design requirements. Use of dynamic TMIN control alleviates the need to design for worst-case conditions and significantly reduces system design and validation time.
Designing for Worst-Case Conditions
System design must always allow for worst-case conditions. In PC design, the worst-case conditions include, but are not limited to the following:
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ADT7468
*
Worst-Case Altitude A computer can be operated at different altitudes. The altitude affects the relative air density, which alters the effectiveness of the fan cooling solution. For example, comparing 40C air temperature at 10,000 ft. to 20C air temperature at sea level, relative air density is increased by 40%. This means that the fan can spin 40% slower and make less noise at sea level than at 10,000 ft. while keeping the system at the same temperature at both locations. Worst-Case Fan Due to manufacturing tolerances, fan speeds in RPM are normally quoted with a tolerance of 20%. The designer needs to assume that the fan RPM can be 20% below tolerance. This translates to reduced system airflow and elevated system temperature. Note that fans 20% out of tolerance can negatively impact system acoustics, because they run faster and generate more noise. Worst-Case Chassis Airflow The same motherboard can be used in a number of different chassis configurations. The design of the chassis and the physical location of fans and components determine the system thermal characteristics. Moreover, for a given chassis, the addition of add-in cards, cables, or other system configuration options can alter the system airflow and reduce the effectiveness of the system cooling solution. The cooling solution can also be inadvertently altered by the end user. (For example, placing a computer against a wall can block the air ducts and reduce system airflow.)
VENTS FAN I/O CARDS I/O CARDS POWER SUPPLY VENTS POWER SUPPLY FAN
*
Worst-Case Assembly Every system manufactured is unique because of manufacturing variations. Heat sinks may be loose fitting or slightly misaligned. Too much or too little thermal grease might be used, or variations in application pressure for thermal interface material could affect the efficiency of the thermal solution. Accounting for manufacturing variations in every system is difficult; therefore, the system must be designed for the worst case.
TA HEAT SINK SA TIMS TTIM CTIM TIMC TTIM
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*
TS CS
CA
THERMAL INTERFACE MATERIAL INTEGRATED HEAT SPREADER
TC
JA
PROCESSOR JTIM SUBSTRATE EPOXY THERMAL INTERFACE MATERIAL
TJ
*
Figure 68. Thermal Model
Although a design usually accounts for worst-case conditions in all these cases, the actual system is almost never operated at worst-case conditions. The alternative to designing for the worst case is to use the dynamic TMIN control function.
Dynamic TMIN Control Overview
GOOD CPU AIRFLOW
CPU
POOR CPU AIRFLOW
CPU
Dynamic TMIN control mode builds upon the basic automatic fan control loop by adjusting the TMIN value based on system performance and measured temperature. This is important, because, instead of designing for the worst case, the system thermals can be defined as operating zones. ADT7468 can selfadjust its fan control loop to maintain either an operating zone temperature or a system target temperature. For example, one can specify that the ambient temperature in a system should be maintained at 50C. If the temperature is below 50C, the fans might not need to run or might run very slowly. If the temperature is higher than 50C, the fans need to throttle up. The challenge presented by any thermal design is finding the right settings to suit the system's fan control solution. This can involve designing for the worst case, followed by weeks of system thermal characterization, and finally fan acoustic optimization (for psycho-acoustic reasons). Getting the most benefit from the automatic fan control mode involves characterizing the system to find the best TMIN and TRANGE settings for the control loop, and the best PWMMIN value for the quietest fan speed setting. Using the ADT7468's dynamic TMIN control mode, however, shortens the characterization time and alleviates tweaking the control loop settings, because the device can selfadjust during system operation. Dynamic TMIN control mode is operated by specifying the operating zone temperatures required for the system. Associated with this control mode are three operating point registers, one
FAN
DRIVE BAYS
DRIVE BAYS
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VENTS GOOD VENTING = GOOD AIR EXCHANGE POOR VENTING = POOR AIR EXCHANGE
Figure 67. Chassis Airflow Issues
*
Worst-Case Processor Power Consumption This data sheet maximum does not necessarily reflect the true processor power consumption. Designing for worstcase CPU power consumption can result in a processor becoming overcooled (generating excess system noise). Worst-Case Peripheral Power Consumption The tendency is to design to data sheet maximums for peripheral components (again overcooling the system).
*
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for each temperature channel. This allows the system thermal solution to be broken down into distinct thermal zones. For example, CPU operating temperature is 70C, VRM operating temperature is 80C, and ambient operating temperature is 50C. The ADT7468 dynamically alters the control solution to maintain each zone temperature as closely as possible to its target operating point.
Operating Point Registers Dynamic TMIN Control Programming
Because the dynamic TMIN control mode is a basic extension of the automatic fan control mode, program the automatic fan control mode parameters first, as described in Step 1 to Step 8, then proceed with dynamic TMIN control mode programming.
STEP 9: OPERATING POINTS FOR TEMPERATURE CHANNELS
The operating point for each temperature channel is the optimal temperature for that thermal zone. The hotter each zone is allowed to be, the quieter the system, because the fans are not required to run as fast. The ADT7468 increases or decreases fan speeds as necessary to maintain the operating point temperature, allowing for system-to-system variation and removing the need for worst-case design. If a sensible operating point value is chosen, any TMIN value can be selected in the system characterization. If the TMIN value is too low, the fans run sooner than required, and the temperature is below the operating point. In response, the ADT7468 increases TMIN to keep the fans off longer and to allow the temperature zone to get closer to the operating point. Likewise, too high a TMIN value causes the operating point to be exceeded, and in turn, the ADT7468 reduces TMIN to turn the fans on sooner to cool the system.
Programming Operating Point Registers
Reg. 0x33, Remote 1 Operating Point = 0xA4 (100C default) Reg. 0x34, Local Operating Point = 0xA4 (100C default) Reg. 0x35, Remote 2 Operating Point = 0xA4 (100C default) Figure 69 shows an overview of the parameters that affect the operation of the dynamic TMIN control loop.
PWM DUTY CYCLE
TLOW
TMIN OPERATING THIGH T THERM TRANGE POINT
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TEMPERATURE
Figure 69. Dynamic TMIN Control Loop
Table 14 provides a brief description of each parameter.
Table 14. TMIN Control Loop Parameters
Parameter TLOW Description If the temperature drops below the TLOW limit, an error flag is set in a status register and an SMBALERT interrupt can be generated. If the temperature exceeds the THIGH limit, an error flag is set in a status register and an SMBALERT interrupt can be generated. The temperature at which the fan turns on under automatic fan speed control. The target temperature for a particular temperature zone. The ADT7468 attempts to maintain system temperature at about the operating point by adjusting the TMIN parameter of the control loop. If the temperature exceeds this critical limit, the fans can be run at 100% for maximum cooling. Programs the PWM duty cycle vs. temperature control slope.
There are three operating point registers, one for each temperature channel. These 8-bit registers allow the operating point temperatures to be programmed with 1C resolution.
Operating Point Registers
Reg. 0x33, Remote 1 Operating Point = 0xA4 (100C default) Reg. 0x34, Local Operating Point = 0xA4 (100C default) Reg. 0x35, Remote 2 Operating Point = 0xA4 (100C default)
THIGH
TMIN Operating point
TTHERM TRANGE
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THERMAL CALIBRATION 100% OPERATING POINT PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 1 MEASUREMENT PWM CONFIG
PWM GENERATOR
PWM1
TMIN REMOTE 2 = CPU TEMP
TRANGE
0% TACH1 PWM CONFIG CPU FAN SINK PWM MIN
THERMAL CALIBRATION
100%
MUX
0% PWM MIN
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 2 MEASUREMENT
PWM GENERATOR
PWM2
TMIN LOCAL = VRM TEMP
TRANGE
TACH2 PWM CONFIG FRONT CHASSIS PWM GENERATOR PWM3
THERMAL CALIBRATION
100%
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 3 AND 4 MEASUREMENT
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0%
TACH3
04499-0-075
REAR CHASSIS
Figure 70. Operating Point Value Dynamically Adjusts Automatic Fan Control Settings
STEP 10: HIGH AND LOW LIMITS FOR TEMPERATURE CHANNELS
The low limit defines the temperature at which the TMIN value starts to be increased, if temperature falls below this value. This has the net effect of reducing the fan speed, allowing the system to get hotter. An interrupt can be generated when the temperature drops below the low limit. The high limit defines the temperature at which the TMIN value starts to be reduced, if temperature increases above this value. This has the net effect of increasing fan speed to cool down the system. An interrupt can be generated when the temperature rises above the high limit.
Programming High and Low Limits
How Dynamic TMIN Control Works
The basic premise is as follows: 1. Set the target temperature for the temperature zone, which could be, for example, the Remote 1 thermal diode. This value is programmed to the Remote 1 operating temperature register. As the temperature in that zone (Remote 1 temperature) rises toward and exceeds the operating point temperature, TMIN is reduced and the fan speed increases. As the temperature drops below the operating point temperature, TMIN is increased and the fan speed is reduced.
2.
3.
There are six limit registers; a high limit and low limit are associated with each temperature channel. These 8-bit registers allow the high and low limit temperatures to be programmed with 1C resolution.
Temperature Limit Registers
However, the loop operation is not as simple as described in these steps. A number of conditions govern the situations in which TMIN can increase or decrease.
Short Cycle and Long Cycle
Reg. 0x4E, Remote 1 Temperature Low Limit = 0x01 Reg. 0x4F, Remote 1 Temperature High Limit = 0x7F Reg. 0x50, Local Temperature Low Limit = 0x01 Reg. 0x51, Local Temperature High Limit = 0x7F Reg. 0x52, Remote 2 Temperature Low Limit = 0x01 Reg. 0x53, Remote 2 Temperature High Limit = 0x7F
The ADT7468 implements two loops: a short cycle and a long cycle. The short cycle takes place every n monitoring cycles. The long cycle takes place every 2n monitoring cycles. The value of n is programmable for each temperature channel. The bits are located at the following register locations: Remote 1 = CYR1 = Bits <2:0> of Calibration Control Register 2 (Address = 0x37).
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Local = CYL = Bits <5:3> of Calibration Control Register 2 (Address = 0x37). Remote 2 = CYR2 = Bits <7:6> of Calibration Control Register 2 and Bit 0 of Calibration Control Register 1 (Address = 0x36).
Table 15. Cycle Bit Assignments
Code 000 001 010 011 100 101 110 111 Short Cycle 8 cycles 16 cycles 32 cycles 64 cycles 128 cycles 256 cycles 512 cycles 1024 cycles (1 s) (2 s) (4 s) (8 s) (16 s) (32 s) (64 s) (128 s) Long Cycle 16 cycles 32 cycles 64 cycles 128 cycles 256 cycles 512 cycles 1024 cycles 2048 cycles (2 s) (4 s) (8 s) (16 s) (32 s) (64 s) (128 s) (256 s)
THERM LIMIT HIGH TEMP LIMIT OPERATING POINT
CURRENT TEMPERATURE MEASUREMENT T1(n) OPERATING POINT TEMPERATURE OP1 WAIT 2n MONITORING CYCLES
IS T1(n) > OP1
YES
DECREASE TMIN BY 1C
NO IS T1(n) < LOW TEMP LIMIT AND TMIN < HIGH TEMP LIMIT YES AND TMIN < OP1 AND T1(n) > TMIN NO
INCREASE TMIN BY 1C
DO NOT CHANGE
Figure 72. Long Cycle Steps
Figure 71 shows the steps taken during the short cycle.
WAIT n MONITORING CYCLES CURRENT TEMPERATURE MEASUREMENT T1(n) OPERATING POINT TEMPERATURE OP1 PREVIOUS TEMPERATURE MEASUREMENT T1 (n - 1)
TMIN
Figure 73. Temperature between Operating Point and Low Temperature Limit
IS T1(n) > (OP1 - HYS) YES
NO
DO NOTHING
Because neither the operating point minus the hysteresis temperature nor the low temperature limit has been exceeded, the TMIN value is not adjusted, and the fan runs at a speed determined by the fixed TMIN and TRANGE values defined in the automatic fan speed control mode.
Example: Operating Point Exceeded--TMIN Reduced
IS T1(n) - T1(n - 1) 0.25C NO
YES
DO NOTHING (SYSTEM IS COOLING OF FOR CONSTANT)
IS T1(n) - T1(n - 1) > 2.0C
DECREASE TMIN BY 2C DECREASE TMIN BY 4C
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IS T1(n) - T1(n - 1) = 0.5 - 0.75C IS T1(n) - T1(n - 1) = 1.0 - 1.75C
DECREASE TMIN BY 1C
When the measured temperature is below the operating point temperature minus the hysteresis, TMIN remains the same. Once the temperature exceeds the operating temperature minus the hysteresis (OP - Hyst), TMIN starts to decrease. This occurs during the short cycle (see Figure 71). The rate at which TMIN decreases depends on the programmed value of n. It also depends on how much the temperature has increased between this monitoring cycle and the last monitoring cycle, that is, if the temperature has increased by 1C, then TMIN is reduced by 2C. Decreasing TMIN has the effect of increasing the fan speed, thus providing more cooling to the system. If the temperature is slowly increasing only in the range (OP - Hyst), that is, 0.25C per short monitoring cycle, then TMIN does not decrease. This allows small changes in temperature in the desired operating zone without changing TMIN. The long cycle makes no change to TMIN in the
Figure 71. Short Cycle Steps
Figure 72 shows the steps taken during the long cycle. The following examples illustrate some of the circumstances that might cause TMIN to increase, decrease, or stay the same.
Example: Normal Operation--No TMIN Adjustment
1.
If measured temperature never exceeds the programmed operating point minus the hysteresis temperature, then TMIN is not adjusted, that is, remains at its current setting. If measured temperature never drops below the low temperature limit, then TMIN is not adjusted.
2.
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Care should be taken when choosing the cycle time. A long cycle time means that TMIN is updated less often. If your system has very fast temperature transients, the dynamic TMIN control loop will always be lagging. If you choose a cycle time that is too fast, the full benefit of changing TMIN might not be realized and needs to change again on the next cycle; in effect, it is overshooting. It is necessary to carry out some calibration to identify the most suitable response time.
HYSTERESIS
ACTUAL TEMP LOW TEMP LIMIT
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ADT7468
temperature range (OP - Hyst), because the temperature has not exceeded the operating temperature. Once the temperature exceeds the operating temperature, the long cycle causes TMIN to be reduced by 1C every long cycle while the temperature remains above the operating temperature. This takes place in addition to the decrease in TMIN that would occur due to the short cycle. In Figure 74, because the temperature is increasing at a rate 0.25C per short cycle, no reduction in TMIN takes place during the short cycle. Once the temperature has fallen below the operating temperature, TMIN stays the same. Even when the temperature starts to increase slowly, TMIN stays the same, because the temperature increases at a rate 0.25C per cycle.
Example: Increase TMIN Cycle
conditions and the reasons they need to be true. TMIN can increase, if * The measured temperature has fallen below the low temperature limit. This means the user must choose the low limit carefully. It should not be so low that the temperature never falls below it, because TMIN would never increase and the fans would run faster than necessary. TMIN is below the high temperature limit. TMIN is never allowed to increase above the high temperature limit. As a result, the high limit should be sensibly chosen, because it determines how high TMIN can go. TMIN is below the operating point temperature. TMIN should never be allowed to increase above the operating point temperature, because the fans would not switch on until the temperature rose above the operating point. The temperature is above TMIN. The dynamic TMIN control is turned off below TMIN.
*
*
When the temperature drops below the low temperature limit, TMIN can increase in the long cycle. Increasing TMIN has the effect of running the fan slower and, therefore, quieter. The long cycle diagram in Figure 74 shows the conditions that need to be true for TMIN to increase. Here is a quick summary of those
THERM LIMIT HIGH TEMP LIMIT OPERATING POINT
*
HYSTERESIS
ACTUAL TEMP
TMIN LOW TEMP LIMIT
NO CHANGE IN TMIN HERE DUE TO ANY CYCLE, BECAUSE T1(n) - T1 (n - 1) 0.25C AND T1(n) < OP = > TMIN STAYS THE SAME
DECREASE HERE DUE TO SHORT CYCLE ONLY T1(n) - T1 (n - 1) = 0.5C OR 0.75C = > TMIN DECREASES BY 1C EVERY SHORT CYCLE
DECREASE HERE DUE TO LONG CYCLE ONLY T1(n) - T1 (n - 1) 0.25C AND T1(n) > OP = > TMIN DECREASES BY 1C EVERY LONG CYCLE
Figure 74. Effect of Exceeding Operating Point Minus Hysteresis Temperature
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Figure 75 shows how TMIN increases when the current temperature is above TMIN and below the low temperature limit, and TMIN is below the high temperature limit and below the operating point. Once the temperature rises above the low temperature limit, TMIN stays the same.
THERM LIMIT HIGH TEMP LIMIT OPERATING POINT
The optimal operating point for the processor is determined by monitoring the thermal monitor in the Intel Pentium 4 processor. To do this, the PROCHOT output of the Pentium 4 is connected to the THERM input of the ADT7468. The operating point for the processor can be determined by allowing the current temperature to be copied to the operating point register when the PROCHOT output pulls the THERM input low on the ADT7468. This gives the maximum temperature at which the Pentium 4 can run before clock modulation occurs.
Enabling the THERM Trip Point as the Operating Point
HYSTERESIS
TMIN
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LOW TEMP LIMIT
ACTUAL TEMP
Bits <4:2> of dynamic TMIN control Register 1 (Reg. 0x36) enable/disable THERM monitoring to program the operating point.
Dynamic TMIN Control Register 1 (0x36) <2> PHTR2 = 1, copies the Remote 2 current temperature to the Remote 2 operating point register, if THERM is asserted. The operating point contains the temperature at which THERM is asserted. This allows the system to run as quietly as possible without affecting system performance. PHTR2 = 0, ignores any THERM assertions. The Remote 2 operating point register reflects its programmed value. <3> PHTL = 1, copies the local current temperature to the local temperature operating point register, if THERM is asserted. The operating point contains the temperature at which THERM is asserted. This allows the system to run as quietly as possible without affecting system performance. PHTL = 0, ignores any THERM assertions. The local temperature operating point register reflects its programmed value.
Figure 75. Increasing TMIN for Quieter Operation
Example: Preventing TMIN from Reaching Full Scale
Because TMIN is dynamically adjusted, it is undesirable for TMIN to reach full scale (127C), because the fan would never switch on. As a result, TMIN is allowed to vary only within a specified range: 1. 2. 3. The lowest possible value for TMIN is -127C (twos complement mode) or -64C (Offset 64 mode). TMIN cannot exceed the high temperature limit. If the temperature is below TMIN, the fan is switched off or is running at minimum speed, and dynamic TMIN control is disabled.
THERM LIMIT OPERATING POINT
HYSTERESIS
LOW TEMP LIMIT HIGH TEMP LIMIT TMIN
ACTUAL TEMP
TMIN PREVENTED FROM INCREASING
04499-0-082
<4> PHTR1 = 1, copies the Remote 1 current temperature to the Remote 1 operating point register, if THERM is asserted. The operating point contains the temperature at which THERM is asserted. This allows the system to run as quietly as possible without affecting system performance. PHTR1 = 0, ignores any THERM assertions. The Remote 1 operating point register reflects its programmed value. Enabling Dynamic TMIN Control Mode Bits <7:5> of dynamic TMIN control Register 1 (Reg. 0x36) enable/disable dynamic TMIN control on the temperature channels. Dynamic TMIN Control Register 1 (0x36) <5> R2T = 1, enables dynamic TMIN control on the Remote 2 temperature channel. The chosen TMIN value is dynamically adjusted based on the current temperature, operating point, and high and low limits for this zone.
Figure 76. TMIN Adjustments Limited by the High Temperature Limit
STEP 11: MONITORING THERM
Using the operating point limit ensures that the dynamic TMIN control mode is operating in the best possible acoustic position while ensuring that the temperature never exceeds the maximum operating temperature. Using the operating point limit allows TMIN to be independent of system-level issues because of its self-corrective nature. In PC design, the operating point for the chassis is usually the worst-case internal chassis temperature.
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R2T = 0, disables dynamic TMIN control. The TMIN value chosen is not adjusted and the channel behaves as described in the Automatic Fan Control Overview section. <6> LT = 1, enables dynamic TMIN control on the local temperature channel. The chosen TMIN value is dynamically adjusted based on the current temperature, operating point, and high and low limits for this zone. LT = 0, disables dynamic TMIN control. The TMIN value chosen is not adjusted and the channel behaves as described in the Automatic Fan Control Overview section. <7> R1T = 1, enables dynamic TMIN control on the Remote 1 temperature channel. The chosen TMIN value is dynamically adjusted based on the current temperature, operating point, and high and low limits for this zone. R1T = 0, disables dynamic TMIN control. The TMIN value chosen is not adjusted and the channel behaves as described in the Automatic Fan Control Overview section.
ENHANCING SYSTEM ACOUSTICS
Automatic fan speed control mode reacts instantaneously to changes in temperature, that is, the PWM duty cycle responds immediately to temperature change. Any impulses in temperature can cause an impulse in fan noise. For psychoacoustic reasons, the ADT7468 can prevent the PWM output from reacting instantaneously to temperature changes. Enhanced acoustic mode controls the maximum change in PWM duty cycle at a given time. The objective is to prevent the fan from cycling up and down, annoying the user.
Acoustic Enhancement Mode Overview
Figure 77 gives a top-level overview of the automatic fan control circuitry on the ADT7468 and shows where acoustic enhancement fits in. Acoustic enhancement is intended as a postdesign tweak made by a system or mechanical engineer evaluating best settings for the system. Having determined the optimal settings for the thermal solution, the engineer can adjust the system acoustics. The goal is to implement a system that is acoustically pleasing without causing user annoyance due to fan cycling. It is important to realize that although a system might pass an acoustic noise requirement specification (for example, 36 dB), if the fan is annoying, it fails the consumer test.
ACOUSTIC ENHANCEMENT
THERMAL CALIBRATION
100%
PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT)
PWM CONFIG
PWM GENERATOR
PWM1
TMIN REMOTE 2 = CPU TEMP
TRANGE
0% PWM MIN TACHOMETER 1 MEASUREMENT TACH1 PWM CONFIG CPU FAN SINK
THERMAL CALIBRATION
100%
MUX
0% PWM MIN
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 2 MEASUREMENT
PWM GENERATOR
PWM2
TMIN LOCAL = VRM TEMP
TRANGE
TACH2 PWM CONFIG FRONT CHASSIS PWM GENERATOR PWM3
THERMAL CALIBRATION
100%
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 3 AND 4 MEASUREMENT
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0%
TACH3
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REAR CHASSIS
Figure 77. Acoustic Enhancement Smoothes Fan Speed Variations under Automatic Fan Speed Control
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Approaches to System Acoustic Enhancement
There are two different approaches to implementing system acoustic enhancement: temperature-centric and fan-centric. The temperature-centric approach involves smoothing transient temperatures as they are measured by a temperature source (for example, Remote 1 temperature). The temperature values used to calculate the PWM duty cycle values are smoothed, reducing fan speed variation. However, this approach causes an inherent delay in updating fan speed and causes the thermal characteristics of the system to change. It also causes the system fans to stay on longer than necessary, because the fan's reaction is merely delayed. The user has no control over noise from different fans driven by the same temperature source. Consider, for example, a system in which control of a CPU cooler fan (on PWM1) and a chassis fan (on PWM2) use Remote 1 temperature. Because the Remote 1 temperature is smoothed, both fans are updated at exactly the same rate. If the chassis fan is much louder than the CPU fan, there is no way to improve its acoustics without changing the thermal solution of the CPU cooling fan. The fan-centric approach to system acoustic enhancement controls the PWM duty cycle, driving the fan at a fixed rate (for example, 6%). Each time the PWM duty cycle is updated, it is incremented by a fixed 6%. As a result, the fan ramps smoothly to its newly calculated speed. If the temperature starts to drop, the PWM duty cycle immediately decreases by 6% at every update. Therefore, the fan ramps smoothly up or down without inherent system delay. Consider, for example, controlling the same CPU cooler fan (on PWM1) and chassis fan (on PWM2) using Remote 1 temperature. The TMIN and TRANGE settings have already been defined in automatic fan speed control mode, that is, thermal characterization of the control loop has been optimized. Now the chassis fan is noisier than the CPU cooling fan. Using the fan-centric approach, PWM2 can be placed into acoustic enhancement mode independently of PWM1. The acoustics of the chassis fan can, therefore, be adjusted without affecting the acoustic behavior of the CPU cooling fan, even though both fans are controlled by Remote 1 temperature. The fan-centric approach is how acoustic enhancement works on the ADT7468.
Enabling Acoustic Enhancement for Each PWM Output Enhance Acoustics Register 1 (Reg. 0x62) <3> = 1, enables acoustic enhancement on PWM1 output. Enhance Acoustics Register 2 (Reg. 0x63) <7> = 1, enables acoustic enhancement on PWM2 output. <3> = 1, enables acoustic enhancement on PWM3 output. Effect of Ramp Rate on Enhanced Acoustics Mode
period, T, the PWM period is subdivided into 255 equal time slots. One time slot corresponds to the smallest possible increment in the PWM duty cycle. A PWM signal of 33% duty cycle is, therefore, high for 1/3 x 255 time slots and low for 2/3 x 255 time slots. Therefore, a 33% PWM duty cycle corresponds to a signal that is high for 85 time slots and low for 170 time slots.
PWM_OUT 33% DUTY CYCLE
85 TIME SLOTS
170 TIME SLOTS PWM OUTPUT (ONE PERIOD) = 255 TIME SLOTS
04499-0-084 04499-0-085
Figure 78. 33% PWM Duty Cycle Represented in Time Slots
The ramp rates in the enhanced acoustics mode are selectable from the values 1, 2, 3, 5, 8, 12, 24, and 48. The ramp rates are discrete time slots. For example, if the ramp rate is 8, then eight time slots are added to the PWM high duty cycle each time the PWM duty cycle needs to be increased. If the PWM duty cycle value needs to be decreased, it is decreased by eight time slots. Figure 79 shows how the enhanced acoustics mode algorithm operates.
READ TEMPERATURE
CALCULATE NEW PWM DUTY CYCLE
IS NEW PWM VALUE > PREVIOUS VALUE? YES INCREMENT PREVIOUS PWM VALUE BY RAMP RATE
NO
DECREMENT PREVIOUS PWM VALUE BY RAMP RATE
Figure 79. Enhanced Acoustics Algorithm
The enhanced acoustics mode algorithm calculates a new PWM duty cycle based on the temperature measured. If the new PWM duty cycle value is greater than the previous PWM value, then the previous PWM duty cycle value is incremented by either 1, 2, 3, 5, 8, 12, 24, or 48 time slots, depending on the settings of the enhance acoustics registers. If the new PWM duty cycle value is less than the previous PWM value, then the previous PWM duty cycle is decremented by 1, 2, 3, 5, 8, 12, 24, or 48 time slots. Each time the PWM duty cycle is incremented or decremented, its value is stored as the previous PWM duty cycle for the next comparison. A ramp rate of 1 corresponds to one time slot, which is 1/255 of the PWM period. In enhanced acoustics mode, incrementing or decrementing by 1 changes the PWM output by 1/255 x 100%.
The PWM signal driving the fan has a period, T, given by the PWM drive frequency, f, because T = 1/f. For a given PWM
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STEP 12: RAMP RATE FOR ACOUSTIC ENHANCEMENT
The optimal ramp rate for acoustic enhancement can be found through system characterization after the thermal optimization has been finished. The effect of each ramp rate should be logged, if possible, to determine the best setting for a given solution.
Enhanced Acoustics Register 1 (Reg. 0x62) <2:0> ACOU, selects the ramp rate for PWM1.
temperature reading is available every 115 ms. With these settings, it takes approximately 0.76 s to go from 33% duty cycle to 100% duty cycle (full speed). Even though the temperature increases very rapidly, the fan ramps up to full speed gradually.
140 RTEMP (C) 120 100 120
100 80 80 60
000 = 1 time slot = 35 s 001 = 2 time slots = 17.6 s 010 = 3 time slots = 11.8 s 011 = 5 time slots = 7 s 100 = 8 time slots = 4.4 s 101 = 12 time slots =3 s 110 = 24 time slots = 1.6 s 111 = 48 time slots = 0.8 s Enhance Acoustics Register 2 (Reg. 0x63)
<2:0> ACOU3, selects the ramp rate for PWM3.
60 PWM CYCLE (%) 40 20 0 0 20
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40
TIME (s)
0 0.76
Figure 80. Enhanced Acoustics Mode with Ramp Rate = 48
000 = 1 time slot = 35 s 001 = 2 time slots = 17.6 s 010 = 3 time slots = 11.8 s 011 = 5 time slots = 7 s 100 = 8 time slots = 4.4 s 101 = 12 time slots = 3 s 110 = 24 time slots = 1.6 s 111 = 48 time slots = 0.8 s
<6:4> ACOU2, selects the ramp rate for PWM2.
Figure 81 shows how changing the ramp rate from 48 to 8 affects the control loop. The overall response of the fan is slower. Because the ramp rate is reduced, it takes longer for the fan to achieve full running speed. In this case, it takes approximately 4.4 s for the fan to reach full speed.
120 RTEMP (C) 100 120 140
100 80 PWM DUTY CYCLE (%) 60 60 40 40 20 20 0
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80
000 = 1 time slot = 35 s 001 = 2 time slots = 17.6 s 010 = 3 time slots = 11.8 s 011 = 5 time slots = 7 s 100 = 8 time slots = 4.4 s 101 = 12 time slots = 3 s 110 = 24 time slots = 1.6 s 111 = 48 time slots = 0.8 s Another way to view the ramp rates is to measure the time it takes for the PWM output to ramp up from 0% to 100% duty cycle for an instantaneous change in temperature. This can be tested by putting the ADT7468 into manual mode and changing the PWM output from 0% to 100% PWM duty cycle. The PWM output takes 35 s to reach 100%, when a ramp rate of 1 time slot is selected. Figure 80 shows remote temperature plotted against PWM duty cycle for enhanced acoustics mode. The ramp rate is set to 48, which corresponds to the fastest ramp rate. Assume that a new
0 0
TIME (s)
4.4
Figure 81. Enhanced Acoustics Mode with Ramp Rate = 8
Figure 82 shows the PWM output response for a ramp rate of 2. In this instance, the fan took about 17.6 s to reach full running speed.
140 RTEMP (C) 120 100 120
100 80 80 PWM DUTY CYCLE (%) 60 40 40 20 0 0 TIME (s) 17.6 20 60
0
Figure 82. Enhanced Acoustics Mode with Ramp Rate = 2
Rev. 0 | Page 58 of 80
ADT7468
Figure 83 shows how the control loop reacts to temperature with the slowest ramp rate. The ramp rate is set to 1, while all other control parameters remain the same. With the slowest ramp rate selected, it takes 35 s for the fan to reach full speed.
120 RTEMP (C) 100 120 100 80 80 60 PWM DUTY CYCLE (%) 40 40 20 20 0 0 TIME (s) 35
04499-0-089
PWM1 Configuration Register (Reg. 0x5C) <3> SLOW, 1 slows the ramp rate for PWM1 by 4. PWM2 Configuration Register (Reg. 0x5D) <3> SLOW, 1 slows the ramp rate for PWM2 by 4. PWM3 Configuration Register (Reg. 0x5E) <3> SLOW, 1 slows the ramp rate for PWM3 by 4.
140
The following sections list the ramp-up times when the SLOW bit is set for each PWM output.
Enhanced Acoustics Register 1 (Reg. 0x62) <2:0> ACOU, selects the ramp rate for PWM1.
60
0
Figure 83. Enhanced Acoustics Mode with Ramp Rate = 1
As Figure 80 to Figure 83 show, the rate at which the fan reacts to temperature change is dependent on the ramp rate selected in the enhanced acoustics registers. The higher the ramp rate, the faster the fan reaches the newly calculated fan speed. Figure 84 shows the behavior of the PWM output as temperature varies. As the temperature increases, the fan speed ramps up. Small drops in temperature do not affect the ramp-up function, because the newly calculated fan speed is still higher than the previous PWM value. Enhanced acoustics mode allows the PWM output to be made less sensitive to temperature variations. This is dependent on the ramp rate selected and programmed into the enhanced acoustics registers.
90 80 70 60 50 40 30 20 10 0
04499-0-090
000 = 140 s 001 = 70.4 s 010 = 47.2 s 011 = 28 s 100 = 17.6 s 101 = 12 s 110 = 6.4 s 111 = 3.2 s Enhance Acoustics Register 2 (Reg. 0x63)
<2:0> ACOU3, selects the ramp rate for PWM3.
000 = 140 s 001 = 70.4 s 010 = 47.2 s 011 = 28 s 100 = 17.6 s 101 = 12 s 110 = 6.4 s 111 = 3.2 s
<6:4> ACOU2, selects the ramp rate for PWM2.
PWM DUTY CYCLE (%)
RTEMP (C)
Figure 84. How Fan Reacts to Temperature Variation in Enhanced Acoustics Mode
000 = 140 s 001 = 70.4 s 010 = 47.2 s 011 = 28 s 100 = 17.6 s 101 = 12 s 110 = 6.4 s 111 = 3.2 s
Slower Ramp Rates
The ADT7468 can be programmed for much longer ramp times by slowing the ramp rates. Each ramp rate can be slowed by a factor of 4.
Rev. 0 | Page 59 of 80
ADT7468 REGISTER TABLES
Table 16. ADT7468 Registers
Address 0x20 0x21 0x22 0x23 0x24 0x25 0x26 0x27 0x28 0x29 0x2A 0x2B 0x2C 0x2D 0x2E 0x2F 0x30 0x31 0x32 0x33 0x34 0x35 0x36 0x37 0x38 0x39 0x3A 0x3D 0x3E 0x3F 0x40 0x41 0x42 R/W R R R R R R R R R R R R R R R R R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R R R R/W R R Description 2.5 V measurement VCCP measurement VCC measurement 5 V measurement 12 V measurement Remote 1 Temperature Local Temperature Remote 2 Temperature TACH1 Low Byte TACH1 High Byte TACH2 Low Byte TACH2 High Byte TACH3 Low Byte TACH3 High Byte TACH4 Low Byte TACH4 High Byte PWM1 Current Duty Cycle PWM2 Current Duty Cycle PWM3 Current Duty Cycle Remote 1 Operating Point Local Temp Operating Point Remote 2 Operating Point Dynamic TMIN Control Reg. 1 Dynamic TMIN Control Reg. 2 Max PWM 1 Duty Cycle Max PWM 2 Duty Cycle Max PWM 3 Duty Cycle Device ID Register Company ID Number Revision Number Configuration 1 Interrupt Status 1 Interrupt Status 2 Bit 7 9 9 9 9 9 9 9 9 7 15 7 15 7 15 7 15 7 7 7 7 7 7 R2T CYR2 7 7 7 7 7 VER VCC = 5V OOL D2 FAULT VIDSEL 7 7 7 7 7 7 7 Bit 6 8 8 8 8 8 8 8 8 6 14 6 14 6 14 6 14 6 6 6 6 6 6 LT CYR2 6 6 6 6 6 VER TODIS R2T D1 FAULT THLD 6 6 6 6 6 6 6 Bit 5 7 7 7 7 7 7 7 7 5 13 5 13 5 13 5 13 5 5 5 5 5 5 R1T CYL 5 5 5 5 5 VER FSPDIS LT FAN4/ THERM VID 5 5 5 5 5 5 5 5 Bit 4 6 6 6 6 6 6 6 6 4 12 4 12 4 12 4 12 4 4 4 4 4 4 PHTR2 CYL 4 4 4 4 4 VER VxI R1T FAN3 Bit 3 5 5 5 5 5 5 5 5 3 11 3 11 3 11 3 11 3 3 3 3 3 3 PHTL CYL 3 3 3 3 3 STP FSPD 5 V/THERM Timer Limit FAN2 Bit 2 4 4 4 4 4 4 4 4 2 10 2 10 2 10 2 10 2 2 2 2 2 2 PHTR1 CYR1 2 2 2 2 2 STP RDY VCC FAN1 Bit 1 3 3 3 3 3 3 3 3 1 9 1 9 1 9 1 9 1 1 1 1 1 1 VCCPLO CYR1 1 1 1 1 1 STP LOCK VCCP THERM Temp Limit VID 1 1 1 1 1 1 1 1 Bit 0 2 2 2 2 2 2 2 2 0 8 0 8 0 8 0 8 0 0 0 0 0 0 CYR2 CYR1 0 0 0 0 0 STP STRT 2.5 V 12 V/VC Default 0x00 0x00 0x00 0x00 0x00 0x01 0x01 0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0xA4 0xA4 0xA4 0x00 0x00 0xFF 0xFF 0xFF 0x68 0x41 0x70 0x01 0x00 0x00 Yes Yes Yes Yes Yes Yes Yes Yes Lockable?
Yes
0x43 0x44 0x45 0x46 0x47 0x48 0x49 0x4A
R/W R/W R/W R/W R/W R/W R/W R/W
VID Config 2.5 V Low Limit 2.5 V High Limit VCCP Low Limit VCCP High Limit VCC Low Limit VCC High Limit 5 V Low Limit
VID 4 4 4 4 4 4 4 4
VID 3 3 3 3 3 3 3 3
VID 2 2 2 2 2 2 2 2
VID 0 0 0 0 0 0 0 0
0x00 0x00 0xFF 0x00 0xFF 0x00 0xFF 0x00
Rev. 0 | Page 60 of 80
ADT7468
Address 0x4B 0x4C 0x4D 0x4E 0x4F 0x50 0x51 0x52 0x53 0x54 0x55 0x56 0x57 0x58 0x59 0x5A 0x5B 0x5C R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W Description 5 V High Limit 12 V Low Limit 12 V High Limit Remote 1 Temp Low Limit Remote 1 Temp High Limit Local Temp Low Limit Local Temp High Limit Remote 2 Temp Low Limit Remote 2 Temp High Limit TACH1 Minimum Low Byte TACH1 Minimum High Byte TACH2 Minimum Low Byte TACH2 Minimum High Byte TACH3 Minimum Low Byte TACH3 Minimum High Byte TACH4 Minimum Low Byte TACH4 Minimum High Byte PWM1 Configuration Register PWM2 Configuration Register PWM3 Configuration Register Remote 1 TRANGE/PWM 1 Frequency Local TRANGE/PWM 2 Frequency Remote 2 TRANGE/PWM3 Frequency Enhance Acoustics Reg. 1 Enhance Acoustics Reg. 2 PWM1 Min Duty Cycle PWM2 Min Duty Cycle PWM3 Min Duty Cycle Remote 1 Temp TMIN Local Temp TMIN Remote 2 Temp TMIN Remote 1 THERM Temp Limit Local THERM Temp Limit Bit 7 7 7 7 7 7 7 7 7 7 7 15 7 15 7 15 7 15 BHVR Bit 6 6 6 6 6 6 6 6 6 6 6 14 6 14 6 14 6 14 BHVR Bit 5 5 5 5 5 5 5 5 5 5 5 13 5 13 5 13 5 13 BHVR Bit 4 4 4 4 4 4 4 4 4 4 4 12 4 12 4 12 4 12 INV Bit 3 3 3 3 3 3 3 3 3 3 3 11 3 11 3 11 3 11 SLOW Bit 2 2 2 2 2 2 2 2 2 2 2 10 2 10 2 10 2 10 SPIN Bit 1 1 1 1 1 1 1 1 1 1 1 9 1 9 1 9 1 9 SPIN Bit 0 0 0 0 0 0 0 0 0 0 0 8 0 8 0 8 0 8 SPIN Default 0xFF 0x00 0xFF 0x01 0x7F 0x01 0x7F 0x01 0x7F 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0x82 Yes Lockable?
0x5D
R/W
BHVR
BHVR
BHVR
INV
SLOW
SPIN
SPIN
SPIN
0x82
Yes
0x5E
R/W
BHVR
BHVR
BHVR
INV
SLOW
SPIN
SPIN
SPIN
0x82
Yes
0x5F
R/W
RANGE
RANGE
RANGE
RANGE
THRM
FREQ
FREQ
FREQ
0XC4
Yes
0x60 0x61
R/W R/W
RANGE RANGE
RANGE RANGE
RANGE RANGE
RANGE RANGE
THRM THRM
FREQ FREQ
FREQ FREQ
FREQ FREQ
0XC4 0XC4
Yes Yes
0x62 0x63 0x64 0x65 0x66 0x67 0x68 0x69 0x6A 0x6B
R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W
MIN3 EN2 7 7 7 7 7 7 7 7
MIN2 ACOU2 6 6 6 6 6 6 6 6
MIN1 ACOU2 5 5 5 5 5 5 5 5
SYNC ACOU2 4 4 4 4 4 4 4 4
EN1 EN3 3 3 3 3 3 3 3 3
ACOU ACOU3 2 2 2 2 2 2 2 2
ACOU ACOU3 1 1 1 1 1 1 1 1
ACOU ACOU3 0 0 0 0 0 0 0 0
0X00 0X00 0X80 0X80 0X80 0X9A 0X9A 0X9A 0XA4 0XA4
Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes
Rev. 0 | Page 61 of 80
ADT7468
Address 0x6C 0x6D R/W R/W R/W Description Remote 2 THERM Temp Limit Remote 1 and Local Temp/TMIN Hysteresis Remote 2 Temp/TMIN Hysteresis XNOR Tree Test Enable Remote 1 Temperature Offset Local Temperature Offset Remote 2 Temperature Offset Configuration Register 2 Interrupt Mask 1 Register Interrupt Mask 2 Register Extended Resolution 1 Extended Resolution 2 Configuration Register 3 THERM Timer Status Register THERM Timer Limit Register TACH Pulses per Revolution Configuration Register 5 Configuration Register 4 Test Register 1 Test Register 2 Bit 7 7 HYSR1 Bit 6 6 HYSR1 Bit 5 5 HYSR1 Bit 4 4 HYSR1 Bit 3 3 HYSL Bit 2 2 HYSL Bit 1 1 HYSL Bit 0 0 HYSL Default 0XA4 0X44 Lockable? Yes Yes
0x6E
R/W
HYSR2
HYSR2
HYSR2
HYRS
RES
RES
RES
RES
0X40
Yes
0x6F 0x70 0x71 0x72 0x73 0x74 0x75 0x76 0x77 0x78 0x79 0x7A 0x7B 0x7C 0x7D 0x7E 0x7F
R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R R/W R/W R/W R/W R R
RES 7 7 7 SHDN OOL D2 5V TDM2 DC4 TMR LIMT FAN4 RES BpAtt 12 V
RES 6 6 6 CONV R2T D1 5V TDM2 DC3 TMR LIMT FAN4 RES BpAtt 5V
RES 5 5 5 ATTN LT F4P VCC LTMP DC2 TMR LIMT FAN3 RES BpAtt VCCP
RES 4 4 4 AVG RIT FAN3 VCC LTMP DC1 TMR LIMT FAN3 RES
RES 3 3 3 AIN4 5V FAN2 VCCP TDM1 FAST TMR LIMT FAN2 GPIOP
RES 2 2 2 AIN3 VCC FAN1 VCCP TDM1 BOOST TMR LIMT FAN2 GPIOD
RES 1 1 1 AIN2 VCCP OVT 2.5 V 12 V THERM TMR LIMT FAN1 LF/HF Pin 14 Func
XEN 0 0 0 AIN1 2.5 V 12 V / VC 2.5 V 12 V ALERT Enable ASRT/TMRO LIMT FAN1 TWOS COMPL Pin 14 Func
0X00 0X00 0X00 0X00 0X00 0X00 0X00 0X00 0X00 0X00 0X00 0X00 0X55 0X00 0X00 0X00 0X00
Yes Yes Yes Yes Yes
Yes
Yes Yes Yes Yes
AINL AINL BpAtt 2.5 V DO NOT WRITE TO THESE REGISTERS DO NOT WRITE TO THESE REGISTERS
Table 17. Voltage Reading Registers (Power-On Default = 0x00)1
Register Address 0x20 0x21 0x22 0x23 0x24 R/W Read-only Read-only Read-only Read-only Read-only Description Reflects the voltage measurement at the 2.5 V input on Pin 22 (8 MSBs of reading). Reflects the voltage measurement2 at the VCCP input on Pin 23 (8 MSBs of reading). Reflects the voltage measurement3 at the VCC input on Pin 4 (8 MSBs of reading). Reflects the voltage measurement at the 5 V input on Pin 20 (8 MSBs of reading. Reflects the voltage measurement at the 12 V input on Pin 21 (8 MSBs of reading).
1 If the extended resolution bits of these readings are also being read, the extended resolution registers (Reg. 0x76, 0x77) must be read first. Once the extended resolution registers have been read, the associated MSB reading registers are frozen until read. Both the extended resolution registers and the MSB registers are frozen. 2 If VCCPLow (Bit 1 of the Dynamic TMIN Control Register 1, 0x36) is set, VCCP can control the sleep state of the ADT7468. 3 VCC (Pin 4) is the supply voltage for the ADT7468.
Rev. 0 | Page 62 of 80
ADT7468
Table 18. Temperature Reading Registers (Power-On Default = 0x01)1, 2, 3
Register Address 0x25 0x26 0x27
1
R/W Read-only Read-only Read-only
Description Remote 1 temperature reading3, 4 (8 MSB of reading). Local temperature reading (8 MSB of reading). Remote 2 temperature reading3, 4 (8 MSB of reading).
If the extended resolution bits of these readings are also being read, the extended resolution registers (Reg. 0x76, 0x77) must be read first. Once the extended resolution registers have been read, all associated MSB reading registers are frozen until read. Both the extended resolution registers and the MSB registers are frozen. 2 These temperature readings can be in twos complement or Offset 64 format; this interpretation is determined by Bit 0 of Configuration Register 5 (0x7C). 3 In twos complement mode, a temperature reading of -128C (0x80) indicates a diode fault (open or short) on that channel. 4 In Offset 64 mode, a temperature reading of -64C (0x00) indicates a diode fault (open or short) on that channel.
Table 19. Fan Tachometer Reading Registers (Power-On Default = 0x00)1
Register Address 0x28 0x29 0x2A 0x2B 0x2C 0x2D 0x2E 0x2F
1
R/W Read-only Read-only Read-only Read-only Read-only Read-only Read-only Read-only
Description TACH1 low byte. TACH1 high byte. TACH2 low byte. TACH2 high byte. TACH3 low byte. TACH3 high byte. TACH4 low byte. TACH4 high byte.
These registers count the number of 11.11 s periods (based on an internal 90 kHz clock) that occur between a number of consecutive fan TACH pulses (default = 2). The number of TACH pulses used to count can be changed using the fan pulses per revolution register (Reg. 0x7B). This allows the fan speed to be accurately measured. Because a valid fan tachometer reading requires that two bytes are read, the low byte must be read first. Both the low and high bytes are then frozen until read. At power-on, these registers contain 0x0000 until such time as the first valid fan TACH measurement is read into these registers. This prevents false interrupts from occurring while the fans are spinning up. A count of 0xFFFF indicates that a fan is one of the following: * Stalled or blocked (object jamming the fan). * Failed (internal circuitry destroyed). * Not populated. (The ADT7468 expects to see a fan connected to each TACH. If a fan is not connected to that TACH, its TACH minimum high and low bytes should be set to 0xFFFF.) * Alternate function, for example, TACH4 reconfigured as THERM pin. * 2-wire instead of 3-wire fan.
Table 20. Current PWM Duty Cycle Registers (Power-On Default = 0x00)1
Register Address 0x30 0x31 0x32
1
R/W Read/write Read/write Read/write
Description PWM1 current duty cycle (0% to 100% duty cycle = 0x00 to 0xFF). PWM2 current duty cycle (0% to 100% duty cycle = 0x00 to 0xFF). PWM3 current duty cycle (0% to 100% duty cycle = 0x00 to 0xFF).
These registers reflect the PWM duty cycle driving each fan at any given time. When in automatic fan speed control mode, the ADT7468 reports the PWM duty cycles back through these registers. The PWM duty cycle values vary according to temperature in automatic fan speed control mode. During fan startup, these registers report back 0x00. In software mode, the PWM duty cycle outputs can be set to any duty cycle value by writing to these registers.
Table 21. Operating Point Registers (Power-On Default = 0x64)1, 2, 3
Register Address 0x33 0x34 0x35
1 2
R/W3 Read/write Read/write Read/write
Description Remote 1 operating point register (default = 100C). Local temperature operating point register (default = 100C). Remote 2 operating point register (default = 100C).
These registers set the target operating point for each temperature channel when the dynamic TMIN control feature is enabled. The fans being controlled are adjusted to maintain temperature about an operating point. 3 These registers become read-only when the Configuration Register 1 lock bit is set to 1. Any subsequent attempts to write to these registers fail.
Rev. 0 | Page 63 of 80
ADT7468
Table 22. Register 0x36--Dynamic TMIN Control Register 1 (Power-On Default = 0x00)1
Bit <0> Name CYR2 R/W Read/write Description MSB of 3-bit remote 2 cycle value. The other two bits of the code reside in Dynamic TMIN Control Register 2 (Reg. 0x37). These three bits define the delay time between making subsequent TMIN adjustments in the control loop, in terms of the number of monitoring cycles. The system has associated thermal time constants that need to be found to optimize the response of fans and the control loop. VCCPLO = 1. When the power is supplied from 3.3 V STANDBY and the core voltage (VCCP) drops below its VCCP low limit value (Reg. 0x46), the following occurs: * Status Bit 1 in Status Register 1 is set. * SMBALERT is generated, if enabled. * PROCHOT monitoring is disabled. * Dynamic TMIN control is disabled. * The device is prevented from entering shutdown. * Everything is re-enabled once VCCP increases above the VCCP low limit. PHTR1 = 1 copies the Remote 1 current temperature to the Remote 1 operating point register, if THERM is asserted. The operating point contains the temperature at which THERM is asserted, which allows the system to run as quietly as possible without affecting system performance. PHTR1 = 0 ignores any THERM assertions on the THERM pin. The Remote 1 operating point register reflects its programmed value. PHTL = 1 copies the local channel's current temperature to the local operating point register, if THERM is asserted. The operating point contains the temperature at which THERM is asserted, which allows the system to run as quietly as possible without affecting system performance. PHTL = 0 ignores any THERM assertions on the THERM pin. The local operating temperature point register reflects its programmed value. PHTR2 = 1 copies the Remote 2 current temperature to the Remote 2 operating point register, if THERM is asserted. The operating point contains the temperature at which THERM is asserted. This allows the system to run as quietly as possible without affecting system performance. PHTR2 = 0 ignores any THERM assertions on the THERM pin. The Remote 2 operating point register reflects its programmed value. R1T = 1 enables dynamic TMIN control on the Remote 1 temperature channel. The chosen TMIN value is dynamically adjusted based on the current temperature, operating point, and high and low limits for this zone. R1T = 0 disables dynamic TMIN control. The TMIN value chosen is not adjusted, and the channel behaves as described in the Fan Speed Control section. LT=1 enables dynamic TMIN control on the local temperature channel. The chosen TMIN value is dynamically adjusted based on the current temperature, operating point, and high and low limits for this zone. LT = 0 disables dynamic TMIN control. The TMIN value chosen is not adjusted, and the channel behaves as described in the Fan Speed Control section. R2T = 1 enables dynamic TMIN control on the Remote 2 temperature channel. The chosen TMIN value is dynamically adjusted based on the current temperature, operating point, and high and low limits for this zone. R2T = 0 disables dynamic TMIN control. The TMIN value chosen is not adjusted, and the channel behaves as described in the Fan Speed Control section.
<1>
VCCPLO
Read/write
<2>
PHTR1
Read/write
<3>
PHTL
Read/write
<4>
PHTR2
Read/write
<5>
R1T
Read/write
<6>
LT
Read/write
<7>
R2T
Read/write
1
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any subsequent attempts to write to this register fail.
Rev. 0 | Page 64 of 80
ADT7468
Table 23. Register 0x37--Dynamic TMIN Control Register 2 (Power-On Default = 0x00)1
Bit <2:0> Name CYR1 R/W Read/write Description 3-Bit Remote 1 Cycle Value. These three bits define the delay time between making subsequent TMIN adjustments in the control loop for the Remote 1 channel, in terms of number of monitoring cycles. The system has associated thermal time constants that need to be found to optimize the response of fans and the control loop. Decrease Cycle Increase Cycle 8 cycles (1 s) 16 cycles (2 s) 16 cycles (2 s) 32 cycles (4 s) 32 cycles (4 s) 64 cycles (8 s) 64 cycles (8 s) 128 cycles (16 s) 128 cycles (16 s) 256 cycles (32 s) 256 cycles (32 s) 512 cycles (64 s) 512 cycles (64 s) 1024 cycles (128 s) 1024 cycles (128 s) 2048 cycles (256 s) 3-bit local temperature cycle value. These three bits define the delay time between making subsequent TMIN adjustments in the control loop for the local temperature channel, in terms of number of monitoring cycles. The system has associated thermal time constants that need to be found to optimize the response of fans and the control loop. Decrease Cycle Increase Cycle 8 cycles (1 s) 16 cycles (2 s) 16 cycles (2 s) 32 cycles (4 s) 32 cycles (4 s) 64 cycles (8 s) 64 cycles (8 s) 128 cycles (16 s) 128 cycles (16 s) 256 cycles (32 s) 256 cycles (32 s) 512 cycles (64 s) 512 cycles (64 s) 1024 cycles (128 s) 1024 cycles (128 s) 2048 cycles (256 s) 2 LSBs of 3-bit Remote 2 cycle value. The MSB of the 3-bit code resides in Dynamic TMIN Control Register 1 (Reg. 0x36). These three bits define the delay time between making subsequent TMIN adjustments in the control loop for the Remote 2 channel, in terms of number of monitoring cycles. The system has associated thermal time constants that need to be found to optimize the response of fans and the control loop. Decrease Cycle 8 cycles (1 s) 16 cycles (2 s) 32 cycles (4 s) 64 cycles (8 s) 128 cycles (16 s) 256 cycles (32 s s) 512 cycles (64 s) 1024 cycles (128 s) Increase Cycle 16 cycles (2 s) 32 cycles (4 s) 64 cycles (8 s) 128 cycles (16 s) 256 cycles (32 s) 512 cycles (64 s) 1024 cycles (128 s) 2048 cycles (256 s)
<5:3>
CYL
Bits 000 001 010 011 100 101 110 111 Read/write
<7:6>
CYR2
Bits 000 001 010 011 100 101 110 111 Read/write
Bits 000 001 010 011 100 101 110 111
1
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any subsequent attempts to write to this register fail.
Table 24. Maximim PWM Duty Cycle (Power-On Default = 0xFF)1, 2
Register Address 0x38 0x39 0x3A
1 2
R/W2 Read/write Read/write Read/write
Description Maximum duty cycle for PWM1 output, default = 100% (0xFF.) Maximum duty cycle for PWM2 output, default = 100% (0xFF). Maximum duty cycle for PWM3 output, default = 100% (0xFF).
These registers set the maximum PWM duty cycle of the PWM output . This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any subsequent attempts to write to this register fail.
Rev. 0 | Page 65 of 80
ADT7468
Table 25. Register 0x40--Configuration Register 1 (Power-On Default = 0x01)
Bit <0> Name STRT R/W Read/write Description Logic 1 enables monitoring and PWM control outputs based on the limit settings programmed. Logic 0 disables monitoring and PWM control based on the default power-up limit settings. Note that the limit values programmed are preserved even if a Logic 0 is written to this bit and the default settings are enabled. This bit becomes read-only and cannot be changed once Bit 1 (LOCK bit) has been written. All limit registers should be programmed by BIOS before setting this bit to 1. (Lockable.) Logic 1 locks all limit values to their current settings. Once this bit is set, all lockable registers become read-only and cannot be modified until the ADT7468 is powered down and powered up again. This prevents rogue programs such as viruses from modifying critical system limit settings. (Lockable.) This bit is set to 1 by the ADT7468 to indicate only that the device is fully powered-up and ready to begin system monitoring. When set to 1, this bit runs all fans at full speed. Power-on default = 0. This bit never gets locked. BIOS should set this bit to a 1 when the ADT7468 is configured to measure current from an ADI ADOPTTM VRM controller and to measure the CPU's core voltage. This bit allows monitoring software to display CPU watts usage. (Lockable.) Logic 1 disables fan spin-up for two TACH pulses. Instead, the PWM outputs go high for the entire fan spin-up timeout selected. When this bit is set to 1, the SMBus timeout feature is enabled. This allows the ADT7468 to be used with SMBus controllers that cannot handle SMBus timeouts. (Lockable.) When this bit is set to 1, the ADT7468 rescales its VCC pin to measure 5 V supply. If this bit is 0, the ADT7468 measures VCC as a 3.3 V supply. (Lockable.)
<1>
LOCK
Write once
<2> <3> <4>
RDY FSPD VxI
Read-only Read/write Read/write
<5> <6> <7>
FSPDIS TODIS VCC
Read/write Read/write Read/write
Table 26. Register 0x41--Interrupt Status Register 1 (Power-On Default = 0x00)
Bit <0> <1> <2> <3> Name 2.5 V VCCP VCC 5 V/ THERM timer R1T LT R2T OOL R/W Read-only Read-only Read-only Read-only Description 2.5 V = 1 indicates that the 2.5 V high or low limit has been exceeded. This bit is cleared on a read of the status register only if the error condition has subsided. VCCP = 1 indicates that the VCCP high or low limit has been exceeded. This bit is cleared on a read of the status register only if the error condition has subsided. VCC = 1 indicates that the VCC high or low limit has been exceeded. This bit is cleared on a read of the status register only if the error condition has subsided. A one indicates the 5 V high or low limit has been exceeded. This bit is cleared on a read of the status register only if the error condition has subsided. If Pin 20 is configured as THERM, this bit is asserted when the Timer Limit has been exceeded. R1T = 1 indicates that the Remote 1 low or high temperature has been exceeded. This bit is cleared on a read of the status register only if the error condition has subsided. LT =1 indicates that the local low or high temperature has been exceeded. This bit is cleared on a read of the status register only if the error condition has subsided. R2T = 1 indicates that the Remote 2 low or high temperature has been exceeded. This bit is cleared on a read of the status register only if the error condition has subsided. OOL = 1 indicates that an out-of-limit event has been latched in Status Register 2. This bit is a logical OR of all status bits in Status Register 2. Software can test this bit in isolation to determine whether any of the voltage, temperature, or fan speed readings represented by Status Register 2 are out-of-limit, which saves the need to read Status Register 2 during every interrupt or polling cycle.
<4> <5> <6> <7>
Read-only Read-only Read-only Read-only
Rev. 0 | Page 66 of 80
ADT7468
Table 27. Register 0x42--Interrupt Status Register 2 (Power-On Default = 0x00)
Bit <0> Name 12V/VC R/W Read-only Description A one indicates that the 12 V high or low limit has been exceeded. This bit is cleared on a read of the status register only if the error condition has subsided. If Pin 21 is configured as VID5, this bit is the VID change bit. This bit is set when the levels on VID0 to VID5 are different than they were 11 s previously. This pin can be used to generate an SMBALERT whenever the VID code changes. OVT = 1 indicates that one of the THERM overtemperature limits has been exceeded. This bit is cleared on a read of the status register when the temperature drops below THERM - THYST. FAN1 = 1 indicates that Fan 1 has dropped below minimum speed or has stalled. This bit is not set when the PWM 1 output is off. FAN2 = 1 indicates that Fan 2 has dropped below minimum speed or has stalled. This bit is not set when the PWM 2 output is off. FAN3 = 1 indicates that Fan 3 has dropped below minimum speed or has stalled. This bit is not set when the PWM 3 output is off. When Pin 14 is programmed as a TACH4 input, F4P = 1 indicates that Fan 4 has dropped below minimum speed or has stalled. This bit is not set when the PWM3 output is off. When Pin 14 is programmed as a GPIO output, writing to this bit determines the logic output of the GPIO. If Pin 14 is configured as the THERM timer input for THERM monitoring, then this bit is set when the THERM assertion time exceeds the limit programmed in the THERM limit register (Reg. 0x7A). D1 = 1 indicates either an open or short circuit on the Thermal Diode 1 inputs. D2 = 1 indicates either an open or short circuit on the Thermal Diode 2 inputs.
<1> <2> <3> <4> <5>
OVT FAN1 FAN2 FAN3 F4P
Read-only Read-only Read-only Read-only Read-only Read/write Read-only
<6> <7>
D1 D2
Read-only Read-only
Table 28. Register 43H--VID Register (Power-On Default = 0x00 )
Bit <4:0> <5> <6> Name VID[4:0] VID5 THLD R/W Read-only Read-only Read/write Description The VID[4:0] inputs from the CPU indicate the expected processor core voltage. On power-up, these bits reflect the state of the VID pins, even if monitoring is not enabled. Reads VID5 from the CPU when Bit 7 = 1. If Bit 7 = 0, then the VID5 bit always reads back 0 (power-on default). Selects the input switching threshold for the VID inputs. THLD = 0 selects a threshold of 1 V (VOL < 0.8 V, VIH > 1.7 V). THLD = 1 lowers the switching threshold to 0.6 V (VOL < 0.4 V, VIH > 0.8 V). VIDSEL = 0 configures Pin 21 as the 12 V measurement input (default).
<7>
VIDSEL
Read/write
Table 29. Voltage Limit Registers1
Register Address 0x44 0x45 0x46 0x47 0x48 0x49 0x4A 0x4B 0x4C 0x4D
1 2
R/W Read/write Read/write Read/write Read/write Read/write Read/write Read/write Read/write Read/write Read/write
Description2 2.5 V. 2.5 V. VCCP low limit. VCCP high limit. VCC low limit. VCC high limit. 5 V low limit. 5 V high limit. 12 V low limit. 12 V high limit.
Power-On Default 0x00 0xFF 0x00 0xFF 0x00 0xFF 0x00 0xFF 0x00 0xFF
Setting the Configuration Register 1 lock bit has no effect on these registers. High Limits: An interrupt is generated when a value exceeds its high limit (> comparison). Low Limits: An interrupt is generated when a value is equal to or below its low limit ( comparison).
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ADT7468
Table 30. Temperature Limit Registers1
Register Address 0x4E 0x4F 0x50 0x51 0x52 0x53 R/W Read/write Read/write Read/write Read/write Read/write Read/write Description2 Remote 1 temperature low limit. Remote 1 temperature high limit. Local temperature low limit. Local temperature high limit. Remote 2 temperature low limit. Remote 2 temperature high limit. Power-On Default 0x81 0x7F 0x81 0x7F 0x81 0x7F
1 Exceeding any of these temperature limits by 1C causes the appropriate status bit to be set in the interrupt status register. Setting the Configuration Register 1 lock bit has no effect on these registers. 2 High Limits: An interrupt is generated when a value exceeds its high limit (> comparison). Low Limits: An interrupt is generated when a value is equal to or below its low limit ( comparison).
Table 31. Fan Tachometer Limit Registers1
Register Address 0x54 0x55 0x56 0x57 0x58 0x59 0x5A 0x5B R/W Read/write Read/write Read/write Read/write Read/write Read/write Read/write Read/write Description TACH1 minimum low byte. TACH1 minimum high byte/Single channel ADC channel select. TACH2 minimum low byte. TACH2 minimum high byte. TACH3 minimum low byte. TACH3 minimum high byte. TACH4 minimum low byte. TACH4 minimum high byte. Power-On Default 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
1 Exceeding any of the TACH limit registers by 1 indicates that the fan is running too slowly or has stalled. The appropriate status bit is set in Interrupt Status Register 2 to indicate the fan failure. Setting the Configuration Register 1 lock bit has no effect on these registers.
Table 32. Register 0x55--TACH 1 Minimum High Byte (Power-On Default = 0xFF)
Bits <4:0> <7:5> Name Reserved SCADC R/W Read-only Read/write Description These bits are reserved when Bit 6 of Config 2 Register (0x73) is set (single-channel ADC mode). Otherwise, these bits represent Bits <4:0> of the TACH1 minimum high byte. When Bit 6 of Config 2 Register (0x73) is set (single channel ADC mode), these bits are used to select the only channel from which the ADC makes measurements. Otherwise, these bits represent Bits <7:5> of the TACH1 minimum high byte.
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ADT7468
Table 33. PWM Configuration Registers
Register Address 0x5C 0x5D 0x5E Bit <2:0> R/W1 Read/write Read/write Read/write R/W Read/write Description Power-On Default PWM1 configuration. 0x82 PWM2 configuration. 0x82 PWM3 configuration. 0x82 Description These bits control the startup timeout for PWMx. The PWM output stays high until two valid TACH rising edges are seen from the fan. If there is not a valid TACH signal during the fan TACH measurement directly after the fan startup timeout period, then the TACH measurement reads 0xFFFF and Status Register 2 reflects the fan fault. If the TACH minimum high and low bytes contain 0xFFFF or 0x0000, then the Status Register 2 bit is not set, even if the fan has not started. 000 = No startup timeout 001 = 100 ms 010 = 250 ms (default) 011 = 400 ms 100 = 667 ms 101 = 1 s 110 = 2 s 111 = 4 s SLOW = 1 makes the ramp rates for acoustic enhancement four times longer. This bit inverts the PWM output. The default is 0, which corresponds to a logic high output for 100% duty cycle. Setting this bit to 1 inverts the PWM output, so 100% duty cycle corresponds to a logic low output. These bits assign each fan to a particular temperature sensor for localized cooling. 000 = Remote 1 temperature controls PWMx (automatic fan control mode). 001 = local temperature controls PWMx (automatic fan control mode). 010 = Remote 2 temperature controls PWMx (automatic fan control mode). 011 = PWMx runs full speed. 100 = PWMx disabled (default). 101 = fastest speed calculated by local and Remote 2 temperature controls PWMx. 110 = fastest speed calculated by all three temperature channel controls PWMx. 111 = manual mode. PWM duty cycle registers (Reg. 0x30 to Reg. 0x32) become writable.
Name SPIN
<3> <4>
SLOW INV
Read/write Read/write
<7:5>
BHVR
Read/write
1
These registers become read-only when the Configuration Register 1 lock bit is set to 1. Any subsequent attempts to write to these registers fail.
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ADT7468
Table 34. TEMP TRANGE/PWM Frequency Registers
Register Address 0x5F 0x60 0x61 Bit Name <2:0> FREQ R/W1 Read/write Read/write Read/write R/W Read/write Description Power-On Default Remote 1 TRANGE/PWM1 frequency. 0xC4 Local temperature TRANGE/PWM2 frequency. 0xC4 Remote 2 TRANGE/PWM3 frequency. 0xC4 Description These bits control the PWMx frequency. 000 = 11.0 Hz 001 = 14.7 Hz 010 = 22.1 Hz 011 = 29.4 Hz 100 = 35.3 Hz (default) 101 = 44.1 Hz 110 = 58.8 Hz 111 = 88.2 Hz THRM = 1 causes the THERM pin (Pin 14/20) to assert low as an output when this temperature channel's THERM limit has been exceeded by 0.25C. The THERM pin remains asserted until the temperature is equal to or below the THERM limit. The minimum time that THERM asserts is one monitoring cycle. This allows clock modulation of devices that incorporate this feature. THRM = 0 makes the THERM pin act as an input only, for example, for Pentium 4 PROCHOT monitoring, when Pin 14/20 is configured as THERM. These bits determine the PWM duty cycle vs. the temperature slope for automatic fan control. 0000 = 2C 0001 = 2.5C 0010 = 3.33C 0011 = 4C 0100 = 5C 0101 = 6.67C 0110 = 8C 0111 = 10C 1000 = 13.33C 1001 = 16C 1010 = 20C 1011 = 26.67C 1100 = 32C (Default) 1101 = 40C 1110 = 53.33C 1111 = 80C
<3>
THRM
Read/write
<7:4>
RANGE
Read/write
1
These registers become read-only when the Configuration Register 1 lock bit is set. Any further attempts to write to these registers have no effect.
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ADT7468
Table 35. Register 0x62--Enhanced Acoustics Register 1 (Power-On Default = 0x00)
Bit <2:0> Name ACOU R/W1 Read/write Description These bits select the ramp rate applied to the PWM1 output. Instead of PWM1 jumping instantaneously to its newly calculated speed, PWM1 ramps gracefully at the rate determined by these bits. This feature enhances the acoustics of the fan being driven by the PWM1 output. Time Slot Increase Time for 33% to 100% 000 = 1 35 s 001 = 2 17.6 s 010 = 3 11.8 s 011 = 4 7s 100 = 8 4.4 s 101 = 12 3s 110 = 24 1.6 s 111 = 48 0.8 s When this bit is 1, acoustic enhancement is enabled on PWM1 output. SYNC = 1 synchronizes fan speed measurements on TACH2, TACH3, and TACH4 to PWM3. This allows up to three fans to be driven from PWM3 output and their speeds to be measured. SYNC = 0 synchronizes only TACH3 and TACH4 to PWM3 output. When the ADT7468 is in automatic fan control mode, this bit defines whether PWM1 is off (0% duty cycle) or at PWM1 minimum duty cycle when the controlling temperature is below its TMIN - hysteresis value. 0 = 0% duty cycle below TMIN - hysteresis. 1 = PWM1 minimum duty cycle below TMIN - hysteresis. When the ADT7468 is in automatic fan speed control mode, this bit defines whether PWM2 is off (0% duty cycle) or at PWM2 minimum duty cycle when the controlling temperature is below its TMIN - hysteresis value. 0 = 0% duty cycle below TMIN - hysteresis. 1 = PWM 2 minimum duty cycle below TMIN - hysteresis. When the ADT7468 is in automatic fan speed control mode, this bit defines whether PWM3 is off (0% duty cycle) or at PWM3 minimum duty cycle when the controlling temperature is below its TMIN - hysteresis value. 0 = 0% duty cycle below TMIN - hysteresis. 1 = PWM3 minimum duty cycle below TMIN - hysteresis.
<3> <4>
EN1 SYNC
Read/write Read/write
<5>
MIN1
Read/write
<6>
MIN2
Read/write
<7>
MIN3
Read/write
1
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.
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ADT7468
Table 36. Register 0x63 - Enhanced Acoustics Register 2 (Power-On Default = 0x00)
Bit <2:0> Name ACOU3 R/W1 Read/write Description These bits select the ramp rate applied to the PWM3 output. Instead of PWM3 jumping instantaneously to its newly calculated speed, PWM3 ramps gracefully at the rate determined by these bits. This effect enhances the acoustics of the fan being driven by the PWM3 output. Time Slot Increase Time for 33% to 100% 000 = 1 35 s 001 = 2 17.6 s 010 = 3 11.8 s 011 = 5 7s 100 = 8 4.4 s 101 = 12 3s 110 = 24 1.6 s 111 = 48 0.8 s When this bit is 1, acoustic enhancement is enabled on PWM3 output. These bits select the ramp rate applied to the PWM2 output. Instead of PWM2 jumping instantaneously to its newly calculated speed, PWM2 ramps gracefully at the rate determined by these bits. This effect enhances the acoustics of the fans being driven by the PWM2 output. Time Slot Increase Time for 33% to 100% 000 = 1 35 s 001 = 2 17.6 s 010 = 3 11.8 s 011 = 5 7s 100 = 8 4.4 s 101 = 12 3s 110 = 24 1.6 s When this bit is 1, acoustic enhancement is enabled on PWM2 output.
<3> <6:4>
EN3 ACOU2
Read/write Read/write
<7>
1
EN2
Read/write
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.
Table 37. PWM Minimum Duty Cycle Registers
Register Address 0x64 0x65 0x66 Bit Name <7:0> PWM duty cycle R/W1 Read/write Read/write Read/write R/W1 Read/write Description PWM1 minimum duty cycle. PWM2 minimum duty cycle. PWM3 minimum duty cycle. Description These bits define the PWMMIN duty cycle for PWMx. 0x00 = 0% duty cycle (fan off ). 0x40 = 25% duty cycle. 0x80 = 50% duty cycle. 0xFF = 100% duty cycle (fan full speed). Power-On Default 0x80 (50% duty cycle) 0x80 (50% duty cycle) 0x80 (50% duty cycle)
1
These registers become read-only when the ADT7468 is in automatic fan control mode.
Table 38. TMIN Registers1
Register Address 0x67 0x68 0x69 R/W2 Read/write Read/write Read/write Description Remote 1 temperature TMIN. Local temperatue TMIN. Remote 2 temperature TMIN. Power-On Default 0x5A (90C) 0x5A (90C) 0x5A (90C)
1 These are the TMIN registers for each temperature channel. When the temperature measured exceeds TMIN, the appropriate fan runs at minimum speed and increases with temperature according to TRANGE. 2 These registers become read-only when the Configuration Register 1 lock bit is set. Any further attempts to write to these registers have no effect.
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ADT7468
Table 39. THERM Limit Registers1
Register Address 0x6A 0x6B 0x6C
1
R/W2 Read/write Read/write Read/write
Description Remote 1 THERM limit. Local THERM limit. Remote 2 THERM limit.
Power-On Default 0x64 (100C) 0x64 (100C) 0x64 (100C)
If any temperature measured exceeds its THERM limit, all PWM outputs drive their fans at 100% duty cycle. This is a fail-safe mechanism incorporated to cool the system in the event of a critical overtemperature. It also ensures some level of cooling in the event that software or hardware locks up. If set to 0x80, this feature is disabled. The PWM output remains at 100% until the temperature drops below THERM limit - hysteresis. If the THERM pin is programmed as an output, then exceeding these limits by 0.25C can cause the THERM pin to assert low as an output. 2 These registers become read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to these registers have no effect.
Table 40. Temperature/TMIN Hysteresis Registers1
Register Address 0x6D <3:0> R/W2 Read/write HYSL Description Remote 1 and local temperature hysteresis. Local temperature hyseresis. 0C to 15C of hysteresis can be applied to the local temperature AFC and dynamic TMIN control loops. Remote 1 temperature hyseresis. 0C to 15C of hysteresis can be applied to the Remote 1 temperature AFC and dynamic TMIN control loops. Remote 2 temperature hysteresis. Local temperature hyseresis. 0C to 15C of hysteresis can be applied to the local temperature AFC and dynamic TMIN control loops. Power-On Default 0x44
<7:4>
HYSR1
0x6E <7:4>
Read/write HYSR2
0x40
Each 4-bit value controls the amount of temperature hysteresis applied to a particular temperature channel. Once the temperature for that channel falls below its TMIN value, the fan remains running at PWMMIN duty cycle until the temperature = TMIN - hysteresis. Up to 15C of hysteresis can be assigned to any temperature channel. The hysteresis value chosen also applies to that temperature channel, if its THERM limit is exceeded. The PWM output being controlled goes to 100%, if the THERM limit is exceeded and remains at 100% until the temperature drops below THERM - hysteresis. For acoustic reasons, it is recommended that the hysteresis value not be programmed less than 4C. Setting the hysteresis value lower than 4C causes the fan to switch on and off regularly when the temperature is close to TMIN. 2 These registers become read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to these registers have no effect.
1
Table 41. XNOR Tree Test Enable
Register Address 0x6F <0> R/W1 Read/write XEN Description XNOR tree test enable register. If the XEN bit is set to 1, the device enters the XNOR tree test mode. Clearing the bit removes the device from the XNOR tree test mode. Unused. Do not write to these bits. Power-On Default 0x00
<7:1>
1
Reserved
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.
Table 42. Remote 1 Temperature Offset
Register Address 0x70 <7:0> R/W1 Read/write Read/write Description Remote 1 temperature offset. Allows a twos complement offset value to be automatically added to or subtracted from the Remote 1 temperature reading. This is to compensate for any inherent system offsets such as PCB trace resistance. LSB value = 0.5C. Power-On Default 0x00
1
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.
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ADT7468
Table 43. Local Temperature Offset
Register Address 0x71 <7:0> R/W1 Read/write Read/write Description Local temperature offset. Allows a twos complement offset value to be automatically added to or subtracted from the local temperature reading. LSB value = 0.5C. Power-On Default 0x00
1
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.
Table 44. Remote 2 Temperature Offset
Register Address 0x72 <7:0> R/W1 Read/write Read/write Description Remote 2 temperature offset. Allows a twos complement offset value to be automatically added to or subtracted from the Remote 2 temperature reading. This is to compensate for any inherent system offsets such as PCB trace resistance. LSB value = 0.5C. Power-On Default 0x00
1
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.
Table 45. Register 0x73--Configuration Register 2 (Power-On Default = 0x00)
Bit 0 Name AIN1 R/W1 Read/write Description AIN1 = 0, speed of 3-wire fans measured using the TACH output from the fan. AIN1 = 1, Pin 6 is reconfigured to measure the speed of 2-wire fans using an external sensing resistor and coupling capacitor. AIN voltage threshold is set via Configuration Register 4 (Reg. 0x7D). Only relevant in low frequency mode. AIN2 = 0, speed of 3-wire fans measured using the TACH output from the fan. AIN2 = 1, Pin 7 is reconfigured to measure the speed of 2-wire fans using an external sensing resistor and coupling capacitor. AIN voltage threshold is set via Configuration Register 4 (Reg. 0x7D). Only relevant in low frequency mode. AIN3 = 0, speed of 3-wire fans measured using the TACH output from the fan. AIN3 = 1, Pin 4 is reconfigured to measure the speed of 2-wire fans using an external sensing resistor and coupling capacitor. AIN voltage threshold is set via Configuration Register 4 (Reg. 0x7D). Only relevant in low frequency mode. AIN4 = 0, speed of 3-wire fans measured using the TACH output from the fan. AIN4 = 1, Pin 9 is reconfigured to measure the speed of 2-wire fans using an external sensing resistor and coupling capacitor. AIN voltage threshold is set via Configuration Register 4 (Reg. 0x7D). Only relevant in low frequency mode. AVG = 1, averaging on the temperature and voltage measurements is turned off. This allows measurements on each channel to be made much faster. ATTN = 1, the ADT7468 removes the attenuators from the 2.5 V, VCCP, 5 V, and 12 V inputs. These inputs can be used for other functions such as connecting up external sensors. It is possible to remove attenuators from individual channels using Bits <7:4> of Configuration Register 4 (0x7D). CONV = 1, the ADT7468 is put into a single-channel ADC conversion mode. In this mode, the ADT7468 can be made to read continuously from one input only, for example, Remote 1 temperature. The appropriate ADC channel is selected by writing to Bits <7:5> of TACH1 minimum high byte register (0x55). Bits <7:5> Reg. 0x55 000 2.5 V 001 VCCP 010 VCC (3.3 V) 011 5V 100 12 V 101 Remote 1 temperature 110 Local temperature 111 Remote 2 temperature SHDN = 1, ADT7468 goes into shutdown mode. All PWM outputs assert low (or high depending on state of INV bit) to switch off all fans. The PWM current duty cycle registers read 0x00 to indicate that the fans are not being driven.
1
AIN2
Read/write
2
AIN3
Read/write
3
AIN4
Read/write
4 5
AVG ATTN
Read/write Read/write
6
CONV
Read/write
7
SHDN
Read/write
1
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect. Rev. 0 | Page 74 of 80
ADT7468
Table 46. Register 0x74--Interrupt Mask Register 1 (Power-On Default <7:0> = 0x00)
Bit 0 1 2 3 4 5 6 7 Name 2.5V VCCP VCC 5V RIT LT R2T OOL R/W Read/write Read/write Read/write Read/write Read/write Read/write Read/write Read/write Description 2.5 V = 1, masks SMBALERT for out-of-limit conditions on the 2.5 V channel. VCCP = 1, masks SMBALERT for out-of-limit conditions on the VCCP channel. VCC = 1, masks SMBALERT for out-of-limit conditions on the VCC channel. 5 V = 1, masks SMBALERT for out-of-limit conditions on the 5 V channel. RIT = 1, masks SMBALERT for out-of-limit conditions on the Remote 1 temperature channel. LT = 1, masks SMBALERT for out-of-limit conditions on the local temperature channel. R2T = 1, masks SMBALERT for out-of-limit conditions on the Remote 2 temperature channel. OOL = 1, masks SMBALERT for any out-of-limit condition in Status Register 2.
Table 47. Register 0x75--Interrupt Mask Register 2 (Power-On Default <7:0> = 0x00)
Bit 0 1 2 3 4 5 Name 12V/VC OVT FAN1 FAN2 FAN3 F4P R/W Read/write Read only Read/write Read/write Read/write Read/write Description When Pin 21 is configured as a 12 V input, 12V/VC = 1 masks SMBALERT for out-of-limit conditions on the 12 V channel. When Pin 21 is programmed as VID5, this bit masks an SMBALERT, if the VID5 VID code bit changes. OVT = 1, masks SMBALERT for overtemperature THERM conditions. FAN1 = 1, masks SMBALERT for a Fan 1 fault. FAN2 = 1, masks SMBALERT for a Fan 2 fault. FAN3 = 1, masks SMBALERT for a Fan 3 fault. If Pin 14 is configured as TACH 4, F4P = 1 masks SMBALERT for a Fan 4 fault. If Pin 14 is configured as THERM, F4P = 1 masks SMBALERT for an exceeded THERM timer limit. If Pin 14 is configured as GPIO, F4P = 1 masks SMBALERT when GPIO is an input and GPIO is asserted. D1 = 1 masks SMBALERT for a diode open or short on a Remote 1 channel. D2 = 1 masks SMBALERT for a diode open or short on a Remote 2 channel.
6 7
D1 D2
Read/write Read/write
Table 48. Register 0x76--Extended Resolution Register 11
Bit <1:0> <3:2> <5:4> <7:6>
1
Name 2.5V VCCP VCC 5V
R/W Read-only Read-only Read-only Read-only
Description 2.5 V LSBs. Holds the 2 LSBs of the 10-bit 2.5 V measurement. VCCP LSBs. Holds the 2 LSBs of the 10-bit VCCP measurement. VCC LSBs. Holds the 2 LSBs of the 10-bit VCC measurement. 5 V LSBs. Holds the 2 LSBs of the 10-bit 5 V measurement.
If this register is read, this register and the registers holding the MSB of each reading are frozen until read.
Table 49. Register 0x77--Extended Resolution Register 21
Bit <1:0> <3:2> <5:4> <7:6>
1
Name 12V TDM1 LTMP TDM2
R/W Read-only Read-only Read-only Read-only
Description 12 V LSBs. Holds the 2 LSBs of the 10-bit 12 V measurement. Remote 1 temperature LSBs. Holds the 2 LSBs of the 10-bit Remote 1 temperature measurement. Local temperature LSBs. Holds the 2 LSBs of the 10-bit local temperature measurement. Remote 2 temperature LSBs. Holds the 2 LSBs of the 10-bit Remote 2 temperature measurement.
If this register is read, this register and the registers holding the MSB of each reading are frozen until read.
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ADT7468
Table 50. Register 0x78--Configuration Register 3 (Power-On Default = 0x00)
Bit <0> Name ALERT R/W1 Read/write Description ALERT = 1, Pin 10 (PWM2/SMBALERT) is configured as an SMBALERT interrupt output to indicate out-of-limit error conditions. ALERT = 0, Pin 10 (PWM2/SMBALERT) is configured as the PWM2 output. THERM Enable = 1 enables THERM functionality on Pin 20 and Pin 14, if Pin 14 is configured as THERM, determined by Bits 0 and 1 (PIN14FUNC) of Configuration Register 4. When THERM is asserted, if the fans are running and the boost bit is set, the fans run at full speed. Alternatively, THERM can be programmed so that a timer is triggered to time how long THERM has been asserted. When THERM is an input and BOOST = 1, assertion of THERM causes all fans to run at the maximum programmed duty cycle for fail-safe cooling. FAST = 1, enables fast TACH measurements on all channels. This increases the TACH measurement rate from once per second to once every 250 ms (4 x). DC1 = 1, enables TACH measurements to be continuously made on TACH1. Fans must be driven by dc. Setting this bit prevents pulse stretching, because it is not required for dc-driven motors. DC2 = 1, enables TACH measurements to be continuously made on TACH2. Fans must be driven by dc. Setting this bit prevents pulse stretching, because it is not required for dc-driven motors. DC3 = 1, enables TACH measurements to be continuously made on TACH3. Setting this bit prevents pulse stretching, because it is not required for dc-driven motors. DC4 = 1, enables TACH measurements to be continuously made on TACH4. Setting this bit prevents pulse stretching, because it is not required for dc-driven motors.
<1>
THERM
Read/write
<2> <3> <4> <5> <6> <7>
1
BOOST FAST DC1 DC2 DC3 DC4
Read/write Read/write Read/write Read/write Read/write Read/write
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.
Table 51. Register 0x79--THERM Timer Status Register (Power-On Default = 0x00)
Bit <7:1> <0> Name TMR ASRT/ TMR0 R/W Read-only Read-only Description Times how long THERM input is asserted. These seven bits read zero until the THERM assertion time exceeds 45.52 ms. This bit is set high on the assertion of the THERM input and is cleared on read. If the THERM assertion time exceeds 45.52 ms, this bit is set and becomes the LSB of the 8-bit TMR reading. This allows THERM assertion times from 45.52 ms to 5.82 s to be reported back with a resolution of 22.76 ms.
Table 52. Register 0x7A--THERM Timer Limit Register (Power-On Default = 0x00)
Bit <7:0> Name LIMT R/W Read/write Description Sets maximum THERM assertion length allowed before an interrupt is generated. This is an 8-bit limit with a resolution of 22.76 ms allowing THERM assertion limits of 45.52 ms to 5.82 s to be programmed. If the THERM assertion time exceeds this limit, Bit 5 (F4P) of Interrupt Status Register 2 (Reg. 0x42) is set. If the limit value is 0x00, then an interrupt is generated immediately on the assertion of the THERM input.
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ADT7468
Table 53. Register 0x7B--TACH Pulses per Revolution Register (Power-On Default = 0x55)
Bit <1:0> Name FAN1 R/W Read/write Description Sets number of pulses to be counted when measuring Fan 1 speed. Can be used to determine fan pulses per revolution for unknown fan type. Pulses Counted 00 = 1 01 = 2 (default) 10 = 3 11 = 4 Sets number of pulses to be counted when measuring Fan 2 speed. Can be used to determine fan pulses per revolution for unknown fan type. Pulses Counted 00 = 1 01 = 2 (default) 10 = 3 11 = 4 Sets number of pulses to be counted when measuring Fan 3 speed. Can be used to determine fan pulses per revolution for unknown fan type. Pulses Counted 00 = 1 01 = 2 (default) 10 = 3 11 = 4 Sets number of pulses to be counted when measuring Fan 4 speed. Can be used to determine fan pulses per revolution for unknown fan type. Pulses Counted 00 = 1 01 = 2 (default) 10 = 3 11 = 4
<3:2>
FAN2
Read/write
<5:4>
FAN3
Read/write
<7:6>
FAN4
Read/write
Table 54. Register 0x7C--Configuration Register 5 (Power-On Default = 0x00)
Bit <0> Name 2sC R/W1 Read/write Description 2sC = 1, sets the temperature range to twos complement temperature range. 2sC = 0, changes the temperature range to Offset 64. When this bit is changed, the ADT7468 interprets all relevant temperature register values as defined by this bit. Sets the PWM drive frequency to high frequency mode (0) or low frequency mode (1). GPIO direction. When GPIO function is enabled, this determines whether the GPIO is an input (0) or an output (1). GPIO polarity. When the GPIO function is enabled and is programmed as an output, this bit determines whether the GPIO is active low (0) or high (1). Unused.
<1> <2> <3> <4:7>
1
HF/LF GPIOD GPIOP RES
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.
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ADT7468
Table 55. Register 0x7D--Configuration Register 4 (Power-On Default = 0x00)
Bit <1:0> Name PIN14FUNC R/W1 Read/write Description These bits set the functionality of Pin 14: 00 = TACH4 (default) 01 = Bidirectional THERM 10 = SMBALERT 11 = GPIO These two bits define the input threshold for 2-wire fan speed measurements (low frequency mode only): 00 = 20 mV 01 = 40 mV 10 = 80 mV 11 = 130 mV Bypass 2.5 V attenuator. When set, the measurement scale for this channel changes from 0 V (0x00) to 2.2965 V (0xFF). Bypass VCCP attenuator. When set, the measurement scale for this channel changes from 0 V (0x00) to 2.2965 V (0xFF). Bypass 5 V attenuator. When set, the measurement scale for this channel changes from 0 V (0x00) to 2.2965 V (0xFF). Bypass 12 V attenuator. When set, the measurement scale for this channel changes from 0 V (0x00) to 2.2965 V (0xFF).
<3:2>
AINL
Read/write
<4> <5> <6> <7>
1
BpAtt2.5V BpAttVCCP BpAtt5V BpAtt12V
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.
Table 56. Register 0x7E--Manufacturer's Test Register 1 (Power-On Default = 0x00)
Bit <7:0> Name Reserved R/W Read-only Description Manufacturer's test register. These bits are reserved for manufacturer's test purposes and should not be written to under normal operation.
Table 57. Register 0x7F--Manufacturer's Test Register 2 (Power-On Default = 0x00)
Bit <7:0> Name Reserved R/W Read-only Description Manufacturer's test register. These bits are reserved for manufacturer's test purposes and should not be written to under normal operation.
Rev. 0 | Page 78 of 80
CONFIGURATION 2 (0X73) VCC LOW LIMIT (0x48) VCC HIGH LIMIT (0x49) TEMPERATURE MEASUREMENT HIGH LIMIT LOW LIMIT (0X4E-0X53) MEASURE FROM 2- OR 3WIRE FANS
VCCP FANTACH 16-BIT MINIMUM LIMIT (0X54-0X5B) INVERT PWM OUTPUT PWM CONFIGURATION (0x5C-0x5E) SLOW IMPROVED ACOUSTIC RAMP-UP REMOTE 1 TEMP CONTROLS SELECTED PWM DRIVE (AFC MODE) MEASUREMENT MSBs (0x25-0x27) MEASUREMENT LSBs (0X77) SOFTWARE INTERRUPTS THERM TIMER LIMIT HAS BEEN EXCEEDED INTERRUPTS ON STATUS REGISTER 2 NO TIMEOUT FAN SPINUP TIMEOUT 100ms 250ms (DEFAULT) 400ms FAN TACH PULSES PER REV (0x7B) 1 PULSE PER REV 2 PULSE PER REV 3 PULSE PER REV 4 PULSE PER REV MAX FAN SPEED (MAX PWM DUTY CYCLE) (0x38-0x3A) FASTEST SPEED CALCULATED BY ALL 3 TEMPERATURE CHANNEL CONTROLS MANUAL MODE. PWM DUTY CYCLE REGISTERS (0x30-0x32) BECOME WRITABLE READY RUN FANS AT FULLSPEED RESCALE VCC (5V/3.3V) CONFIGURATION 3 (0x78) ENABLE THERM THERM BOOST (FAN MUST BE RUNNING) FAST TACH MEASUREMENTS CONFIGURE PIN 10 ENABLE CONTINUOUS FAN SPEED MEASUREMENT CHANGE CYCLE TIME
(ONLY USED WHEN FANS ARE POWERED BY DC AND NOT PWM)
VCC VCC MEASUREMENT (0x22)
TEMPERATURE OFFSET (0x70-0x72)
REMOTE TEMP1
FAN 16-BIT MEASUREMENT (0x28-0x2F)
REMOTE TEMP2
AVERAGE TEMP AND VOLTAGE MEASUREMENTS RESCALE VCCP INPUT (5V/3.3V) SINGLE CHANNEL ADC MODE SHUTDOWN
LOCAL TEMP FAN BEHAVIOR LOCAL TEMP CONTROLS SELECTED PWM DRIVE (AFC MODE) REMOTE 2 TEMP CONTROLS SELECTED PWM DRIVE (AFC MODE) SELECTED PWM DRIVE RUNS FULL SPEED SELECTED PWM DRIVE DISABLED (DEFAULT) CONFIGURATION 1 (0X40) START MONITORING LOCK SETTINGS FASTEST SPEED CALCULATED BY LOCAL AND REMOTE 2 TEMP CONTROLS SELECTED PWM DRIVE TEMPERATURE MEASUREMENT (0X25, 0X26,0X27)
LOW BYTE MUST BE READ FIRST. WHEN THE LOW BYTE IS READ, REGISTERS ARE LOCKED UNTIL THE ASSOCIATED HIGH BYTE IS READ.
SELECTED PWM RAMP-UP SPEED
35s (33%-100%)
17.6s (33%-100%)
ENHANCE ACOUSTICS (0x62,0x63)
IF THESE REGISTERS ARE USED, ALL TEMPERATURE MEASUREMENT MSB REGISTERS ARE FROZEN UNTIL ALL TEMPERATURE MEASUREMENT MSB REGISTERS ARE READ.
18s (33%-100%)
ENABLE SELECTED PWM RAMP-UP SPEED 667ms 1s 2s 4s
7s (33%-100%)
4.4s (33%-100%)
DRIVE PWM OUTPUTS HIGH/LOW
SYNC FAN SPEED MEASUREMENTS
3s (33%-100%)
1.6s (33%-100%)
ALLOW SELECTED PWM TO TURN OFF WHEN TEMP IS BELOW TMIN-HYST
0.8s (33%-100%)
TEMPERATURE MEASURED IS OUT OF LIMITS DIODE FAULT. FOR REMOTE CHANNELS ONLY FAN FAULT INTERRUPT STATUS (0x41, 0x42) MASK INTERRUPT? (0x74,0x75) F4P
PWM DUTY CYCLE (MANUAL MODE ONLY) (0x30-0x32)
TMIN. MIN TEMP THAT CAUSES SELECTED FANS TO RUN (0x67-0x69) AUTOMATIC FAN CONTROL PWMMIN DUTY CYCLE (AUTOMATIC MODE ONLY) (0X64-0X66)
HARDWARE INTERRUPTS THERM CONFIGURATION 4 (0x7D) SET PIN 14/20 FUNCTIONALITY TACH 4 THERM SMBALERT GPIO PWM 2 SMBALERT TEMPERATURE RANGE 20mV 40mV 80mV 130mV 8 CYCLES (1s) 16 CYCLES (2s) 32 CYCLES (4s) 64 CYCLES (8s) BYPASS VCCP ATTENUATOR INPUT THRESHOLD FOR 2-WIRE FANS (AINL) OFFSET 64 TWOS COMPLEMENT CONFIGURATION 5 (0X7C) SMBALERT
ADT7468 PROGRAMMING BLOCK DIAGRAM
TEMPERATURE HYSTERESIS (THYST) (0x6D, 0x6E) DYNAMIC TMIN CONTROL (0x36, 0x37) ENABLE DYNAMIC TMIN CONTROL ON INDIVIDUAL CHANNEL THERM TIMER LIMIT (0x7A) THERM AS (TIMER) INPUT VCCP LOW (SLEEP) INCREASE CYCLE TIME 16 CYCLES (2s) 32 CYCLES (4s) 64 CYCLES (8s) 128 CYCLES (16s) 256 CYCLES (32s) 512 CYCLES (64s) 1024 CYCLES (128s) 2048 CYCLES (256s) TEMPERATURE VOLTAGES FANS INTERRUPT GENERAL THERM DECREASE CYCLE TIME VCCP LOW LIMIT (0x46) VCCP HIGH LIMIT (0x47) THERM TIMER STATUS (0x79) CYXX TMIN ADJUSTMENT CYCLE TIME PHTXX CURRENT TEMPERATURE OF SELECTED CHANNEL IS COPIED TO RELEVANT OPERATING POINT REGISTER ON ASSERTION OF THERM
Figure 85.
VCCP MEASUREMENT (0x47) 128 CYCLES (16s) 256 CYCLES (32s) 512 CYCLES (64s) 1024 CYCLES (128s) THERM TEMP LIMITS (0x6A, 0x6B, 0x6C) XNOR Test (0x6F) AVERAGE TEMP AND VOLTAGE MEASUREMENTS (SEE CONFIGURATION 2, 0x73)
ADT7467/ADT7468 PROGRAMMING BLOCK DIAGRAM
ADT7468
04498-0-044
PWM DUTY CYCLE/RELATIVE FAN SPEED
AUTOMATIC FAN CONTROL TEMPERATURE 100% DUTY CYCLE MAX PWM HEATING COOLING TRANGE = SLOPE MIN PWM 0% DUTY CYCLE THYST TMIN THYST T THERM
Rev. 0 | Page 79 of 80
OPERATING POINT (0x33-0x35)
TEMP TRANGE,PWM FREQ,THERMENABLE (0x5F, 0x60, 0x61)
THERM IS INPUT/OUTPUT
2C
FAN DRIVE HIGH/LOW FREQUENCY MODE GPIO DIRECTION GPIO POLARITY
TRANGE
2.5C
PWM FREQUENCY
11.0Hz
3.33C
14.7Hz
4C
22.1Hz
5C
29.4Hz
6.67C
35.3Hz
8C
44.1Hz
10C
58.8Hz
13.33C
THERM AS OVERTEMP OUTPUT
88.2Hz
16C
20C
26.67C
32C
40C
53.33C
80C
ADT7468 OUTLINE DIMENSIONS
0.341 BSC
24
13
0.154 BSC
1 12
0.236 BSC
PIN 1 0.065 0.049 0.069 0.053
0.010 0.004 COPLANARITY 0.004
0.025 BSC
0.012 0.008
SEATING PLANE
0.010 0.006
8 0
0.050 0.016
COMPLIANT TO JEDEC STANDARDS MO-137AE
Figure 86. 24-Lead Shrink Small Outline Package [QSOP] (RQ-24) Dimensions shown in inches
ORDERING GUIDE
Model ADT7468ARQ ADT7468ARQ-REEL ADT7468ARQ-REEL7 Temperature Range -40C to +120C -40C to +120C -40C to +120C Package Description 24-Lead QSOP 24-Lead QSOP 24-Lead QSOP Package Option RQ-24 RQ-24 RQ-24
(c) 2004 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D04499-0-4/04(0)
Rev. 0 | Page 80 of 80
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