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dBCoolTM Remote Thermal Controller and Voltage Monitor ADT7476A
FEATURES
Monitors up to five voltages Improved TACH and PWM performance Controls and monitors up to four fans High and low frequency fan drive signal One on-chip and two remote temperature sensors Extended temperature measurement range up to 191C 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) Pentium(R) 4 processor Thermal control circuit via THERM input 3-wire and 4-wire fan speed measurement Limit comparison of all monitored values 5 V support on all TACH and PWM channels Meets SMBus 2.0 electrical specifications
GENERAL DESCRIPTION
The ADT7476A dBCOOL controller is a thermal monitor and multiple PWM fan controller for noise-sensitive or powersensitive applications requiring active system cooling. The ADT7476A can drive a fan using either a low or high frequency drive signal and can monitor the temperature of up to two remote sensor diodes plus its own internal temperature. The part also measures and controls the speed of up to four fans, so the fans operate at the lowest possible speed for minimum acoustic noise. The automatic fan speed control loop optimizes fan speed for a given temperature. The effectiveness of the system's thermal solution can be monitored using the THERM input. The ADT7476A 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
ADDR ADDREN SELECT SCL SDA SMBALERT VID5/GPIO5 VID4/GPIO4 VID3/GPIO3 VID2/GPIO2 VID1/GPIO1 VID0/GPIO0 GPIO6 PWM1 PWM2 PWM3 TACH1 TACH2 TACH3 TACH4 PWM REGISTERS AND CONTROLLERS (HF AND LF)
ADT7476A
VID/GPIO REGISTER SMBus ADDRESS SELECTION SERIAL BUS INTERFACE ADDRESS POINTER REGISTER AUTOMATIC FAN SPEED CONTROL PWM CONFIGURATION REGISTERS INTERRUPT MASKING
FAN SPEED COUNTER
PERFORMANCE MONITORING THERM VCC TO ADT7476A THERMAL PROTECTION ACOUSTIC ENHANCEMENT CONTROL INPUT SIGNAL CONDITIONING AND ANALOG MULTIPLEXER INTERRUPT STATUS REGISTERS
VCC D1+ D1- D2+ D2- +5VIN +12VIN +2.5VIN VCCP
10-BIT ADC
LIMIT COMPARATORS
BAND GAP REFERENCE BAND GAP TEMP. SENSOR GND
VALUE AND LIMIT REGISTERS
05742-001
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: 781.461.3113 (c)2006 Analog Devices, Inc. All rights reserved.
ADT7476A TABLE OF CONTENTS
Features .............................................................................................. 1 General Description ......................................................................... 1 Functional Block Diagram .............................................................. 1 Revision History ............................................................................... 2 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 Feature Comparisons Between ADT7476A and ADT7468.. 10 Recommended Implementation............................................... 10 Serial Bus Interface..................................................................... 11 Write Operations ........................................................................ 14 Read Operations ......................................................................... 14 SMBus Timeout .......................................................................... 15 Virus Protection.......................................................................... 15 Voltage Measurement Input...................................................... 15 Analog-to-Digital Converter .................................................... 15 Input Circuitry............................................................................ 15 Voltage Measurement Registers................................................ 16 Voltage Limit Registers .............................................................. 16 Extended Resolution Registers ................................................. 16 Additional ADC Functions for Voltage Measurements ........ 16 VID Code Monitoring ............................................................... 18 VID Code Input Threshold Voltage......................................... 18 VID Code Change Detect Function ........................................ 18 Programming the GPIOs........................................................... 18 Temperature Measurement Method ........................................ 18 Factors Affecting Diode Accuracy........................................... 20 Additional ADC Functions for Temperature Measurement 21 Limits, Status Registers, and Interrupts....................................... 23 Limit Values ................................................................................ 23 Status Registers ........................................................................... 24 THERM Timer ........................................................................... 26 Fan Drive Using PWM Control ............................................... 29 Laying Out 3-Wire Fans ............................................................ 31 Programming TRANGE.................................................................. 34 Programming the Automatic Fan Speed Control Loop ............ 35 Manual Fan Control Overview................................................. 35 THERM Operation in Manual Mode...................................... 35 Automatic Fan Control Overview............................................ 35 Step 1--Hardware Configuration ............................................ 37 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 6--TRANGE for Temperature Channels.............................. 44 Step 7--TTHERM for Temperature Channels ............................. 46 Step 8--THYST for Temperature Channels................................ 48 Fan Presence Detect................................................................... 49 Fan Sync....................................................................................... 50 Standby Mode ............................................................................. 50 XNOR Tree Test Mode .............................................................. 50 Power-On Default ...................................................................... 50 Register Tables ................................................................................ 51 Outline Dimensions ....................................................................... 71 Ordering Guide .......................................................................... 71
REVISION HISTORY
1/06--Revision 0: Initial Version
Rev. 0 | Page 2 of 72
ADT7476A SPECIFICATIONS
TA = TMIN to TMAX, VCC = VMIN to VMAX, unless otherwise noted. 1 Table 1.
Parameter POWER SUPPLY Supply Voltage Supply Current, ICC TEMP-TO-DIGITAL CONVERTER Local Sensor Accuracy Resolution Remote Diode Sensor Accuracy Resolution Remote Sensor Source Current Min 3.0 Typ 3.3 1.5 0.5 0.25 0.5 Max 3.6 3 1.5 2.5 1.5 2.5 Unit V mA C C C C C C A % % LSB %/V ms ms ms ms ms k k % % RPM RPM RPM RPM 8.0 0.4 20 0.4 1.0 mA V A V A V V mV Test Conditions/Comments
Interface inactive, ADC active 0C TA 85C -40C TA 125C 0C TA 85C -40C TA 125C High level Low level For 12 V channel For all other channels 8 bits Averaging enabled Averaging enabled Averaging enabled Averaging enabled Averaging disabled For VCCP channel For all other channels 0C TA 70C -40C TA +120C Fan count = 0xBFFF Fan count = 0x3FFF Fan count = 0x0438 Fan count = 0x021C
0.25 180 11 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 Full-Scale Count Nominal Input RPM
2 1.5 1
70 70
0.1 11 12 38 145 19 120 114 6 10 65,535 109 329 5,000 10,000
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) 2 Input High Voltage, VIH Input Low Voltage, VIL Hysteresis
0.1
IOUT = -8.0 mA VOUT = VCC IOUT = -4.0 mA VOUT = VCC
0.1 2.0
0.4 500
Rev. 0 | Page 3 of 72
ADT7476A
Parameter 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 SCL Low Time, tLOW SCL High Time, tHIGH SCL, SDA Rise Time, tr SCL, SDA Fall Time, tf Data Setup Time, tSU;DAT Detect Clock Low Timeout, tTIMEOUT
1
Min 2.0
Typ
Max
Unit V V V V V p-p V V A A pF
Test Conditions/Comments
5.5 0.8 0.5 0.75 x VCC 0.4 1 1 5 10 4.7 4.7 4.0 400 50
Maximum input voltage Minimum input voltage
VIN = VCC VIN = 0 See Figure 2
50 1,000 300 35
250 15
kHz ns s s s ns s ns ms
Can be optionally disabled
All voltages are measured with respect to GND, unless otherwise specified. Typical voltages are TA = 25C and probably represent a parametric norm. Logic inputs accept input high voltages up to VMAX, even when the 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. 2 SMBus timing specifications are guaranteed by design and are not production tested.
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 72
05742-002
ADT7476A ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Positive Supply Voltage (VCC) Maximum Voltage on +12 VIN Pin Maximum Voltage on +5 VIN Pin Maximum Voltage on All Open-Drain Outputs Max Voltage on TACH/PWM Pins Voltage on Remaining Input or Output Pins Input Current at Any Pin Package Input Current Maximum Junction Temperature (TJMAX) Storage Temperature Range Lead Temperature, Soldering IR Reflow Peak Temperature Pb-Free Peak Temperature Lead Temperature (Soldering, 10 sec) ESD Rating Rating 3.6 V 16 V 6.25 V 3.6 V +5.5 V -0.3 V to +4.2 V 5 mA 20 mA 150C -65C to +150C 220C 260C 300C 1500 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
JA is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages. Table 3. Thermal Resistance
Package Type 24-lead QSOP JA 122 JC 31.25 Unit C/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 72
ADT7476A PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
SDA SCL GND VCC VID0/GPIO0 VID1/GPIO1 VID2/GPIO2 VID3/GPIO3 TACH3
1 2 3 4 5 6 7 8 9 24 23 22 21
PWM1/XTO VCCP +2.5VIN/THERM +12VIN/VID5 +5VIN VID4/GPIO4 D1+ D1- D2+ D2-
05742-003
ADT7476A
TOP VIEW (Not to Scale)
20 19 18 17 16 15 14 13
PWM2/SMBALERT 10 TACH1 11 TACH2 12
TACH4/THERM/SMBALERT/GPIO6/ADDR SELECT PWM3/ADDREN
Figure 3. Pin Configuration
Table 4. Pin Function Descriptions
Pin No. 1 2 3 4 5 6 7 8 9 10 Mnemonic SDA SCL GND VCC VID0/ GPIO0 VID1/ GPIO1 VID2/ GPIO2 VID3/ GPIO3 TACH3 PWM2/ SMBALERT 11 12 13 TACH1 TACH2 PWM3 ADDREN 14 TACH4/ THERM/ Description Digital I/O (Open Drain). SMBus bidirectional serial data. Requires SMBus pull-up. Digital Input (Open Drain). SMBus serial clock input. Requires SMBus pull-up. Ground Pin. Power Supply. Powered by 3.3 V standby, if monitoring in low power states is required. VCC is also monitored through this pin. Digital Input. Voltage supply readouts from CPU. This value is read into the VID/GPIO register (0x43). General-Purpose Open Drain Digital I/O. Digital Input. Voltage supply readouts from CPU. This value is read into the VID/GPIO register (0x43). General-Purpose Open Drain Digital I/O. Digital Input. Voltage supply readouts from CPU. This value is read into the VID/GPIO register (0x43). General-Purpose Open Drain Digital I/O. Digital Input. Voltage supply readouts from CPU. This value is read into the VID/GPIO register (0x43). General-Purpose Open Drain Digital I/O. Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 3. 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-oflimit conditions. Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 1. Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 2. Digital I/O (Open Drain). Pulse width modulated output to control the speed of Fan 3 and Fan 4. Requires 10 k typical pull-up. Can be configured as a high or low frequency drive. If pulled low on power-up, the ADT7476A enters address select mode, and the state of Pin 14 (ADDR SELECT) determines the ADT7476A's slave address. Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 4. Alternatively, the pin can be reconfigured as a bidirectional THERM pin. Times and monitors assertions on the THERM input. For example, it can be connected to the PROCHOT output of Intel's Pentium 4 processor or to the output of a trip point temperature sensor. Can 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-oflimit conditions. General-Purpose Open Drain Digital I/O. If in address select mode, the logic state of this pin defines the SMBus device address. Cathode Connection to Second Thermal Diode. Anode Connection to Second Thermal Diode. Cathode Connection to First Thermal Diode. Anode Connection to First Thermal Diode.
SMBALERT/ GPIO6/ ADDR SELECT D2- D2+ D1- D1+
15 16 17 18
Rev. 0 | Page 6 of 72
ADT7476A
Pin No. 19 20 21 22 Mnemonic VID4/ GPIO4 +5VIN +12VIN/ VID5 +2.5VIN/ THERM Description Digital Input. Voltage supply readouts from CPU. This value is read into the VID/GPIO register (0x43). General-Purpose Open Drain Digital I/O. Analog Input. Monitors 5 V power supply. Analog Input. Monitors 12 V power supply. Digital Input. Voltage supply readouts from CPU. This value is read into the VID/GPIO register (0x43). Analog Input. Monitors 2.5 V supply, typically a chipset voltage. Alternatively, this pin can be reconfigured as a bidirectional/omnidirectional THERM pin. Can be used to time and monitor assertions on the THERM input. For example, can be connected to the PROCHOT output of Intel's Pentium 4 processor or to the output of a trip point temperature sensor. Can be used as an output to signal overtemperature conditions. Analog Input. Monitors processor core voltage (0 V to 3 V). Digital Output (Open Drain). Pulse width modulated output to control the speed of Fan 1. Requires 10 k typical pull-up. Also functions as the output from the XOR tree in XOR test mode.
23 24
VCCP PWM1/ XTO
Rev. 0 | Page 7 of 72
ADT7476A TYPICAL PERFORMANCE CHARACTERISTICS
0 70 60 -10
TEMPERATURE ERROR (C)
TEMPERATURE ERROR (C)
50 40 30 100mV 20 40mV 10
05742-008
-20
-30
-40
60mV
-50
05742-004
0 -10 0 100M 200M 300M 400M 500M NOISE FREQUENCY (Hz)
-60 0 2 4 6 8 10 12 14 16 18 20 22 CAPACITANCE (nF)
600M
Figure 4. Temperature Error vs. Capacitance Between D+ and D-
Figure 7. Remote Temperature Error vs. Differential-Mode Noise Frequency
30 20
1.20 1.18 1.16
TEMPERATURE ERROR (C)
10 D+ TO GND 0 D+ TO VCC -10 -20
1.14 1.12
IDD (mA)
1.10 1.08 1.06 1.04 1.02
05742-006
1.00 0.98 3.0 3.1 3.2 3.3 VDD (V) 3.4 3.5 3.6
-40 0 20 40 60 80 LEAKAGE RESISTANCE (M)
100
Figure 5. Remote Temperature Error vs. PCB Resistance
Figure 8. Normal IDD vs. Power Supply
30
15
25
TEMPERATURE ERROR (C)
100mV
TEMPERATURE ERROR (C)
10
20 15 10 5 0 40mV -5 0 100M 200M 300M 400M 500M NOISE FREQUENCY (Hz)
5 100mV 0 250mV -5
60mV
-10
05742-007
-15 0 100M 200M 300M 400M 500M FREQUENCY (Hz)
600M
600M
Figure 6. Remote Temperature Error vs. Common-Mode Noise Frequency
Figure 9. Internal Temperature Error vs. Power Supply Noise Frequency
Rev. 0 | Page 8 of 72
05742-010
05742-009
-30
ADT7476A
6 4 250mV
TEMPERATURE ERROR (C)
3.0 2.5
TEMPERATURE ERROR (C)
2 0 -2 100mV -4 -6 -8
05742-011
2.0 1.5 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 -40 -20 0 20 40 60 85 105 125 OIL BATH TEMPERATURE (C)
05742-013
-10 -12 0 100M 200M 300M 400M 500M FREQUENCY (Hz)
600M
Figure 10. Remote Temperature Error vs. Power Supply Noise Frequency
Figure 12. Remote Temperature Error vs. ADT7476A Temperature
3.0 2.5
TEMPERATURE ERROR (C)
2.0 1.5 1.0 0.5 0 -0.5 -1.0 -1.5 -40 -20 0 20 40 60 85 105 125 OIL BATH TEMPERATURE (C)
05742-012
Figure 11. Internal Temperature Error vs. ADT7476A Temperature
Rev. 0 | Page 9 of 72
ADT7476A PRODUCT DESCRIPTION
The ADT7476A 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 ADT7476A are performed over the serial bus. In addition, a pin can be reconfigured as an SMBALERT output to signal out-of-limit conditions. * * * * * * The ADT7476A offers increased temperature accuracy on all temperature channels. The ADT7476A defaults to twos complement temperature measurement mode. Some pins have swapped/added functions. The power-up routine for the ADT7476A is simplified. The ADT7476A has a higher maximum input voltage TACH/PWM spec, supporting a wider range of fans. VCORE_LOW_ENABLE has been reallocated to Bit 7 of Configuration Register 1 (0x40).
FEATURE COMPARISONS BETWEEN ADT7476A AND ADT7468
* Dynamic TMIN , dynamic operating point, and associated registers are no longer available in the ADT7476A. The following related registers are gone: o o o * Calibration Control 1 (0x36) Calibration Control 2 (0x37) Operating Point (0x33, 0x34, and 0x35)
RECOMMENDED IMPLEMENTATION
Configuring the ADT7476A as shown in Figure 13 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 4. CPU temperature measured using Remote 1 temperature channel. Remote temperature zone measured through Remote 2 temperature channel. Local temperature zone measured through the internal 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.
Previously (in the ADT7468), TRANGE defined the slope of the automatic fan control algorithm. TRANGE now defines a true temperature range (in the ADT7476A). Acoustic filtering is now assigned to temperature zones, not to fans. Available smoothing times have been increased for better acoustic performance. Temperature measurements are now made with two switching currents instead of three. SRC is not available in the ADT7476A. High frequency PWM can now be enabled/disabled on each PWM output individually. THERM can now be enabled/disabled on each temperature channel individually. The ADT7476A does not support full shutdown mode.
*
*
* * *
Rev. 0 | Page 10 of 72
ADT7476A
ADT7476A
FRONT CHASSIS FAN PWM1 TACH2 TACH1
REAR CHASSIS FAN
PWM3 TACH3 VID[0:4]/VID[0:5] D2+ D2- THERM
5(VRM9)/6(VRM10)
AMBIENT TEMPERATURE
D1+ D1-
PROCHOT
VCC +5VIN
SDA SCL
+12VIN/VID5 SMBALERT
05742-014
GND
Figure 13. ADT7476A Configuration
SERIAL BUS INTERFACE
Control of the ADT7476A is carried out using the serial system management bus (SMBus). The ADT7476A is connected to this bus as a slave device, under the control of a master controller. The ADT7476A has a 7-bit serial bus address. When the device is powered up with Pin 13 (PWM3/ADDREN) high, the ADT7476A has a default SMBus address of 0101110 or 0x2E. The read/write bit must be added to get the 8-bit address. If more than one ADT7476A is to be used in a system, each ADT7476A is placed in ADDR SELECT mode by strapping Pin 13 low on power-up. The logic state of Pin 14 then determines the device's SMBus address. The logic of these pins is sampled on power-up. The device address is sampled on power-up and latched on the first valid SMBus transaction, more precisely on the low-tohigh transition at the beginning of the eighth SCL pulse, when the serial bus address byte matches the selected slave address. The selected slave address is chosen using the ADDREN pin/ ADDR SELECT pin. Any attempted changes in the address have no effect after this. Table 5. Hardwiring the ADT7476A SMBus Device Address
Pin 13 State 0 0 1 Pin 14 Low (10 k to GND) High (10 k pull-up) Don't Care Address 0101100 (0x2C) 0101101 (0x2D) 0101110 (0x2E)
ADT7476A
ADDR SELECT 14
VCC
10k 13 ADDRESS = 0x2E
05742-015 05742-017 05742-016
PWM3/ADDREN
Figure 14. Default SMBus Address = 0x2E
ADT7476A
ADDR SELECT 14 10k
PWM3/ADDREN
13 ADDRESS = 0x2C
Figure 15. SMBus Address = 0x2C (Pin 14 = 0)
VCC
ADT7476A
10k ADDR SELECT 14
PWM3/ADDREN
13
ADDRESS = 0x2D
Figure 16. SMBus Address = 0x2D (Pin 14 = 1)
Rev. 0 | Page 11 of 72
ADT7476A
VCC
3.
ADT7476A
10k ADDR SELECT 14
PWM3/ADDREN
13
NC
DO NOT LEAVE ADDREN UNCONNECTED! CAN CAUSE UNPREDICTABLE ADDRESSES. CARE SHOULD BE TAKEN TO ENSURE THAT PIN 13 (PWM3/ADDREN) IS EITHER TIED HIGH OR LOW. LEAVING PIN 13 FLOATING COULD CAUSE THE ADT7476A TO POWER UP WITH AN UNEXPECTED ADDRESS. NOTE THAT IF THE ADT7476A IS PLACED INTO ADDR SELECT MODE, PINS 13 AND 14 CANNOT BE USED AS THE ALTERNATIVE FUNCTIONS (PWM3, TACH4/THERM) UNLESS THE CORRECT CIRCUIT IS MUXED IN AT THE CORRECT TIME OR DESIGNED TO HANDLE THESE DUAL FUNCTIONS.
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 10th 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 10th clock pulse, and then high during the 10th clock pulse to assert a stop condition.
Figure 17. Unpredictable SMBus Address if Pin 13 is Unconnected
The ability to make hardwired changes to the SMBus slave address allows the user to avoid conflicts with other devices sharing the same serial bus, for example, if more than one ADT7476A is used in a system. The serial bus protocol operates as follows: 1. The master initiates data transfer by establishing a start condition, which is defined as a high-to-low transition on the serial data line SDA while the serial clock line SCL remains high. This indicates that an address/data stream follows. All slave peripherals connected to the serial bus respond to the start condition and shift in the next eight bits, consisting of a 7-bit address (MSB first), plus a R/W bit, which determine the direction of the data transfer, that is, whether data is written to or read from the slave device. The peripheral whose address corresponds to the transmitted address responds by pulling the data line low during the low period before the ninth clock pulse, known as the acknowledge bit. All other devices on the bus now remain idle while the selected device waits for data to be read from or written to it. If the R/W bit is a 0, the master writes to the slave device. If the R/W bit is a 1, the master reads from the slave device. 2. 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. A low-to-high transition, when the clock is high, can be interpreted as a stop signal. The number of data bytes transmitted over the serial bus in a single read or write operation is limited only by what the master and slave devices can handle.
Any number of bytes of data can be transferred over the serial bus in one operation. However, 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 ADT7476A, write operations contain either one or two bytes, and read operations contain one byte. To write data to one of the device data registers or read data from it, the address pointer register must be set so 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 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 18. 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: 1. If the ADT7476A's address pointer register value is unknown, or not the desired value, then 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 ADT7476A as before, but only the data byte containing the register address is sent, because no data is written to the register (see Figure 19). 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 (see Figure 20.) 2. If the address pointer register is already known to be at the desired address, data can be read from the corresponding data register without first writing to the address pointer register (see Figure 20).
05742-018
Rev. 0 | Page 12 of 72
ADT7476A
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 ADT7476A also supports the read byte protocol. See Intel's System Management Bus Specifications Rev. 2 for more information. 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.
1 SCL
9
1
9
SDA START BY MASTER
0
1
0
1
1
A1
A0
R/W ACK. BY ADT7476A
D7
D6
D5
D4
D3
D2
D1
D0 ACK. BY ADT7476A
FRAME 1 SERIAL BUS ADDRESS BYTE
FRAME 2 ADDRESS POINTER REGISTER BYTE 9
1 SCL (CONTINUED)
SDA (CONTINUED)
D7
D6
D5
D4
D3
D2
D1
D0 ACK. BY STOP BY ADT7476A MASTER
FRAME 3 DATA BYTE
Figure 18. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register
1 SCL
9
1
9
SDA START BY MASTER
0
1
0
1
1
A1
A0
R/W ACK. BY ADT7476A
D7
D6
D5
D4
D3
D2
D1
D0
05742-020
05742-021
FRAME 1 SERIAL BUS ADDRESS BYTE
FRAME 2 ADDRESS POINTER REGISTER BYTE
ACK. BY ADT7476A
STOP BY MASTER
Figure 19. Writing to the Address Pointer Register Only
1 SCL
9
1
9
SDA START BY MASTER
0
1
0
1
1
A1
A0
R/W ACK. BY ADT7476A
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 ADT7476A
Figure 20. Reading Data from a Previously Selected Register
Rev. 0 | Page 13 of 72
05742-019
ADT7476A
WRITE OPERATIONS
The SMBus specification defines several protocols for different types of read and write operations. The ones used in the ADT7476A are discussed below. The following abbreviations are used in the diagrams: * * * * * * S - START P - STOP R - READ W - WRITE A - ACKNOWLEDGE A - NO ACKNOWLEDGE
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. 5. 6. 7. 8. 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. 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, and the transaction ends.
The ADT7476A 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. 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 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.
This operation is illustrated in Figure 22.
1 2 3 4 REGISTER ADDRESS 5 A 6 DATA 78 AP
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SLAVE S ADDRESS W A
Figure 22. Single-Byte Write to a Register
READ OPERATIONS
The ADT7476A uses the following SMBus read protocols.
Receive Byte
This operation is useful when repeatedly reading a single register. The register address is set up beforehand. In this operation, the master device receives a single byte from a slave device, as follows: 1. 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.
For the ADT7476A, 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 21.
1 S 2 3 4 REGISTER ADDRESS 56 AP
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2. 3. 4. 5. 6.
SLAVE WA ADDRESS
Figure 21. 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.
In the ADT7476A, 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 23.
1 2 3 4 DATA 56 AP
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SLAVE S ADDRESS R A
Figure 23. Single-Byte Read from a Register
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ADT7476A
Alert Response Address
Alert response address (ARA) is a feature of SMBus devices, allowing 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: 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 this device is now known and can be interrogated per usual. 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 ADT7476A responds to the alert response address, the master must read the status registers, and SMBALERT is cleared only if the error condition goes away.
VOLTAGE MEASUREMENT INPUT
The ADT7476A has four external voltage measurement channels. It can also measure its own supply voltage, VCC. Pin 20 to Pin 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). The 2.5 V input can be used to monitor a chipset supply voltage in computer systems.
ANALOG-TO-DIGITAL CONVERTER
All analog inputs are multiplexed into the on-chip, successiveapproximation, analog-to-digital converter, which 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 the tolerance of these supply voltages, the ADC produces an output of 3/4 full scale (768 dec or 300 hex) for the nominal input voltage, giving it adequate headroom to cope with overvoltages.
3.
4.
INPUT CIRCUITRY
The internal structure for the analog inputs is shown in Figure 24. 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
5.
SMBus TIMEOUT
The ADT7476A includes an SMBus timeout feature. If there is no SMBus activity for 35 ms, the ADT7476A assumes 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 if necessary, it can be disabled.
5VIN 93k
47k
30pF
3.3VIN
68k 71k 30pF MUX
Configuration Register 1 (0x40)
[6] TODIS = 0, SMBus timeout enabled (default). [6] TODIS = 1, SMBus timeout disabled.
2.5VIN
45k 94k 30pF
VCCP
17.5k 52.5k 35pF
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VIRUS PROTECTION
To prevent rogue programs or viruses from accessing critical ADT7476A register settings, the lock bit can be set. Setting Bit 1 of Configuration Register 1 (0x40) sets the lock bit and locks critical registers. In this mode, certain registers can no longer be written to until the ADT7476A is powered down and powered up again. For more information on which registers are locked, see Table 18.
Figure 24. Structure of Analog Inputs
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ADT7476A
VOLTAGE MEASUREMENT REGISTERS
Register 0x20, 2.5 V Reading = 0x00 default Register 0x21, VCCP Reading = 0x00 default Register 0x22, VCC Reading = 0x00 default Register 0x23, 5 V Reading = 0x00 default Register 0x24, 12 V Reading = 0x00 default
ADDITIONAL ADC FUNCTIONS FOR VOLTAGE MEASUREMENTS
A number of other functions are available on the ADT7476A to offer the system designer increased flexibility.
Turn-Off Averaging
For each voltage/temperature measurement read from a value register, 16 readings have been made internally and the results averaged before being placed into the value register. When faster conversions are needed, setting Bit 4 of Configuration Register 2 (0x73) turns averaging off. This effectively gives a reading 16 times faster but the reading can be noisier. The default round robin cycle time takes 146.5 ms. Table 6. Conversion Time with Averaging Disabled
Channel Voltage Channels Remote Temperature 1 Remote Temperature 2 Local Temperature Measurement Time (ms) 0.7 7 7 1.3
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. Register 0x44, 2.5 V Low Limit = 0x00 default Register 0x45, 2.5 V High Limit = 0xFF default Register 0x46, VCCP Low Limit = 0x00 default Register 0x47, VCCP High Limit = 0xFF default Register 0x48, VCC Low Limit = 0x00 default Register 0x49, VCC High Limit = 0xFF default Register 0x4A, 5 V Low Limit = 0x00 default Register 0x4B, 5 V High Limit = 0xFF default Register 0x4C, 12 V Low Limit = 0x00 default Register 0x4D, 12 V High Limit = 0xFF default Table 9 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.
When Bit 7 of Configuration Register 6 (0x10) is set, the default round robin cycle time increases to 240 ms.
Bypass All Voltage Input Attenuators
Setting Bit 5 of Configuration Register 2 (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.
Bypass Individual Voltage Input Attenuators
Bits [7:4] of Configuration Register 4 (0x7D) can be used to bypass individual voltage channel attenuators. Table 7. Bypassing Individual Voltage Input Attenuators
Configuration Register 4 (0x7D) Bit Channel Attenuated 4 Bypass 2.5 V attenuator 5 Bypass VCCP attenuator 6 Bypass 5 V attenuator 7 Bypass 12 V attenuator
EXTENDED RESOLUTION REGISTERS
Voltage measurements can be made with higher accuracy using the extended resolution registers (0x76 and 0x77). Whenever the extended resolution registers are read, the corresponding data in the voltage measurement registers (0x20 to 0x24) is locked until their data is read. That is, if extended resolution is required, then the extended resolution register must be read first, immediately followed by the appropriate voltage measurement register.
Configuration Register 2 (0x73)
[4] = 1, averaging off. [5] = 1, bypass input attenuators. [6] = 1, single-channel convert mode.
TACH1 Minimum High Byte (0x55)
[7:5] Selects ADC channel for single-channel convert mode.
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ADT7476A
Single-Channel ADC Conversion
While single-channel mode is intended as a test mode that can be used to increase sampling times for a specific channel, and therefore helps to analyze that channel's performance in greater detail, it can also have other applications. Setting Bit 6 of Configuration Register 2 (0x73) places the ADT7476A into single-channel ADC conversion mode. In this mode, the ADT7476A can only read a single voltage channel. The selected voltage 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). Table 8. Programming Single-Channel ADC Mode
Bits [7:5] Register 0x55 000 001 010 011 100 101 110 111
1
Channel Selected 1 2.5 V VCCP VCC 5V 12 V Remote 1 temperature Local temperature Remote 2 temperature
In the process of configuring single-channel ADC conversion mode, the TACH1 minimum high byte is also changed, possibly trading off TACH1 minimum high byte functionality with single-channel mode functionality.
Table 9. 10-Bit A/D Output Code vs. VIN
12 VIN <0.0156 0.0156 to 0.0312 0.0312 to 0.0469 0.0469 to 0.0625 0.0625 to 0.0781 0.0781 to 0.0937 0.0937 to 0.1093 0.1093 to 0.1250 0.1250 to 0.14060 5 VIN <0.0065 0.0065 to 0.0130 0.0130 to 0.0195 0.0195 to 0.0260 0.0260 to 0.0325 0.0325 to 0.0390 0.0390 to 0.0455 0.0455 to 0.0521 0.0521 to 0.0586 * * * 1.6675 to 1.6740 * * * 3.3300 to 3.3415 * * * 5.0025 to 5.0090 * * * 6.5983 to 6.6048 6.6048 to 6.6113 6.6113 to 6.6178 6.6178 to 6.6244 6.6244 to 6.6309 6.6309 to 6.6374 6.6374 to 6.4390 6.6439 to 6.6504 6.6504 to 6.6569 6.6569 to 6.6634 >6.6634 Input Voltage VCC (3.3 VIN) <0.0042 0.0042 to 0.0085 0.0085 to 0.0128 0.0128 to 0.0171 0.0171 to 0.0214 0.0214 to 0.0257 0.0257 to 0.0300 0.0300 to 0.0343 0.0343 to 0.0386 2.5 VIN <0.0032 0.0032 to 0.0065 0.0065 to 0.0097 0.0097 to 0.0130 0.0130 to 0.0162 0.0162 to 0.0195 0.0195 to 0.0227 0.0227 to 0.0260 0.0260 to 0.0292 VCCP <0.00293 0.0293 to 0.0058 0.0058 to 0.0087 0.0087 to 0.0117 0.0117 to 0.0146 0.0146 to 0.0175 0.0175 to 0.0205 0.0205 to 0.0234 0.0234 to 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 to 4.0156
1.1000 to 1.1042
0.8325 to 0.8357
0.7500 to 0.7529
256 (1/4 scale)
01000000 00
8.0000 to 8.0156
2.2000 to 2.2042
1.6650 to 1.6682
1.5000 to 1.5029
512 (1/2 scale)
10000000 00
12.0000 to 12.0156
3.3000 to 3.3042
2.4975 to 2.5007
2.2500 to 2.2529
768 (3/4 scale)
11000000 00
15.8281 to 15.8437 15.8437 to 15.8593 15.8593 to 15.8750 15.8750 to 15.8906 15.8906 to 15.9062 15.9062 to 15.9218 15.9218 to 15.9375 15.9375 to 15.9531 15.9531 to 15.9687 15.9687 to 15.9843 >15.9843
4.3527 to 4.3570 4.3570 to 4.3613 4.3613 to 4.3656 4.3656 to 4.3699 4.3699 to 4.3742 4.3742 to 4.3785 4.3785 to 4.3828 4.3828 to 4.3871 4.3871 to 4.3914 4.3914 to 4.3957 >4.3957
3.2942 to 3.2974 3.2974 to 3.3007 3.3007 to 3.3039 3.3039 to 3.3072 3.3072 to 3.3104 3.3104 to 3.3137 3.3137 to 3.3169 3.3169 to 3.3202 3.3202 to 3.3234 3.3234 to 3.3267 >3.3267
2.9677 to 2.9707 2.9707 to 2.9736 2.9736 to 2.9765 2.9765 to 2.9794 2.9794 to 2.9824 2.9824 to 2.9853 2.9853 to 2.9882 2.9882 to 2.9912 2.9912 to 2.9941 2.9941 to 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
Rev. 0 | Page 17 of 72
ADT7476A
VID CODE MONITORING
The ADT7476A has five dedicated voltage ID (VID code) inputs. These are digital inputs that can be read back through the VID/GPIO register (0x43) to determine the processor voltage required or the system being used. 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. the logic state of Pin 21. Bit 0 of Interrupt Status Register 2 (0x42) reflects VID code changes.
VID CODE CHANGE DETECT FUNCTION
The ADT7476A has a VID code change detect function. When Pin 21 is configured as the VID5 input, VID code changes are detected and reported back by the ADT7476A. Bit 0 of Interrupt Status Register 2 (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 is used to generate an SMBALERT interrupt. If an SMBALERT interrupt is not required, Bit 0 of Interrupt Mask Register 2 (0x75), when set, prevents SMBALERTs from occurring on VID code changes.
VID/GPIO Register (0x43)
[0] = VID0, reflects logic state of Pin 5. [1] = VID1, reflects logic state of Pin 6. [2] = VID2, reflects logic state of Pin 7. [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.
Interrupt Status Register 2 (0x42)
[0] 12V/VC = 0, if Pin 21 is configured as VID5, Logic 0 denotes no change in VID code within the last 11 s. [0] 12V/VC = 1, if Pin 21 is configured as VID5, 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.
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/GPIO register (0x43) controls the VID input threshold voltage.
PROGRAMMING THE GPIOS
The ADT7476A follows an upgrade path from the ADM1027 to the ADT7476A. In order to maintain consistency between versions, it is necessary to omit references to GPIO5. As a result, there are six GPIOs as follows: GPIO0, GPIO1, GPIO2, GPIO3, GPIO4, and GPIO6. Setting Bit 4 of Configuration Register 5 (0x7C) to 1 enables GPIO functionality. This turns all pins configured as VID inputs into general-purpose outputs. Writing to the corresponding VID bit in the VID/GPIO register (0x43) sets the polarity for the corresponding GPIO. GPIO6 can be programmed independently as, for example, an input or output, using Bits [3:2] of Configuration Register 5 (0x7C).
VID/GPIO Register (0x43)
[6] THLD = 0, VID switching threshold = 1 V, VOL < 0.8 V, VIH > 1.7 V, VMAX = 3.3 V. [6] 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/GPIO register (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 a sixth VID input.
TEMPERATURE MEASUREMENT METHOD
Local Temperature Measurement
The ADT7476A 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 temperature registers (Addresses 0x25, 0x26, and 0x27). 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 10 and Table 11. Theoretically, the temperature sensor and ADC can measure temperatures from -63C 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 ADT7476A operating temperature range are not possible.
VID/GPIO Register (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 VID/GPIO Register (0x43) always reads back 0. Bit 0 of Interrupt Status Register 2 (0x42) reflects 12 V out-of-limit measurements. [7] 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
Rev. 0 | Page 18 of 72
ADT7476A
Table 10. Twos Complement Temperature Data Format
Temperature -128C -50C -25C -10C 0C +10.25C +25.5C +50.75C +75C +100C +125C +127C
1
This is given by VBE = 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 25 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, which is provided on some microprocessors for temperature monitoring. It could also be a discrete transistor such as a 2N3904/2N3906.
VDD CPU I NxI IBIAS
Digital Output (10-Bit) 1000 0000 00 (diode fault) 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
1
Bold numbers denote 2 LSB of measurement in Extended Resolution Register 2 (0x77) with 0.25C resolution.
Table 11. Extended Range, Temperature Data Format
Temperature -64C -1C 0C +1C +10C +25C +50C +75C +100C +125C +191C
1
THERMDA REMOTE SENSING TRANSISTOR
D+
VOUT+ TO ADC
Digital Output (10-Bit)1 0000 0000 00 (diode fault) 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
THERMDC
D-
BIAS DIODE
VOUT-
05742-026
LOW-PASS FILTER fC = 65kHz
Figure 25. Signal Conditioning for Remote Diode Temperature Sensors
Bold numbers denote 2 LSB of measurement in Extended Resolution Register 2 (0x77) with 0.25C resolution.
If a discrete transistor is used, the collector is not grounded and is 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 26 and Figure 27 show how to connect the ADT7476A 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.
ADT7476A
Remote Temperature Measurement
05742-027
The ADT7476A can measure the temperature of two remote diode sensors or diode-connected transistors connected to Pin 17 and Pin 18, or Pin 15 and Pin 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. As a result, this technique is unsuitable for mass production. The technique used in the ADT7476A is to measure the change in VBE when the device is operated at two different currents.
2N3904 NPN
D+ D-
Figure 26. Measuring Temperature Using an NPN Transistor
ADT7476A
D+
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2N3906 PNP
D-
Figure 27. Measuring Temperature Using a PNP Transistor
Rev. 0 | Page 19 of 72
ADT7476A
To measure VBE, the sensor switches between operating currents of I and N x I. The resulting waveform passes through a 65 kHz low-pass filter to remove noise and through a chopperstabilized amplifier. The amplifier performs the amplification and rectification of the waveform to produce a dc voltage proportional to VBE. This voltage is measured by the ADC to give a temperature output in 10-bit, twos complement format. To further reduce the effects of noise, digital filtering is performed by averaging the results of 16 measurement cycles. A remote temperature measurement takes nominally 38 ms. The results of remote temperature measurements are stored in 10-bit, twos complement format, as illustrated in Table 10. The extra resolution for the temperature measurements is held in the Extended Resolution Register 2 (0x77). This gives temperature readings with a resolution of 0.25C. To factor this in, the user can write the T value to the offset register. The ADT7476A 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 ADT7476A, IHIGH, is 180 A, and the low level current, ILOW, is 11 A. If the ADT7476A current levels do not match the current levels specified by the CPU manufacturer, it could be necessary to remove an offset. The CPU's 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, then the algebraic sum of these offsets must be programmed to the offset register.
Noise Filtering
For temperature sensors operating in noisy environments, previous practice placed a capacitor across the D+ pin and the D- pin 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, which makes using the sensor difficult in a very noisy environment. In most cases, a capacitor is not required because differential inputs by their very nature have a high immunity to noise.
If a discrete transistor is used with the ADT7476A, the best accuracy is obtained by choosing devices according to the following criteria: * * * * Base-emitter voltage greater than 0.25 V at 11 A, at the highest operating temperature. Base-emitter voltage less than 0.95 V at 180 A, at the lowest operating temperature. Base resistance less than 100 . Small variation in the current gain, hFE, (approximately 50 to 150) that indicates tight control of VBE characteristics.
FACTORS AFFECTING DIODE ACCURACY
Remote Sensing Diode
The ADT7476A is designed to work with 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 ADT7476A 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's data sheet for the nf values): T = (nf - 1.008) x (273.15 K + T)
Transistors, such as 2N3904, 2N3906, or equivalents in SOT-23 packages, are suitable devices to use.
Nulling Out Temperature Errors
As CPUs run faster, it is 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 can 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 ADT7476A has temperature offset registers (0x70 and 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 a twos complement 8-bit reading to every temperature measurement. Changing Bit 1 of Configuration Register 5 (0x7C) changes the resolution and therefore, the range of the temperature offset as either having a -63C to +127C range with a resolution of 1C or having a -63C to +64C range with a resolution of 0.5C. This temperature offset can be used to compensate for linear temperature errors introduced by noise.
Rev. 0 | Page 20 of 72
ADT7476A
Temperature Offset Registers
Register 0x70, Remote 1 Temperature Offset = 0x00 (0C default) Register 0x71, Local Temperature Offset = 0x00 (0C default) Register 0x72, Remote 2 Temperature Offset = 0x00 (0C default)
Reading Temperature from the ADT7476A
It is important to note that temperature can be read from the ADT7476A 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. Extended Resolution Register 2 (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.
ADT7463/ADT7476A Backwards Compatible Mode
By setting Bit 0 of Configuration Register 5 (0x7C), all temperature measurements are stored in the zone temperature reading registers (0x25, 0x26, and 0x27) in twos complement in the -63C to +127C range. 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 (-63C to +191C), the fault condition is represented by -64C = 0000 0000.
ADDITIONAL ADC FUNCTIONS FOR TEMPERATURE MEASUREMENT
A number of other functions are available on the ADT7476A to offer the system designer increased flexibility.
Temperature Reading Registers
Register 0x25, Remote 1 Temperature Register 0x26, Local Temperature Register 0x27, Remote 2 Temperature Register 0x77, Extended Resolution 2 = 0x00 default [7:6] TDM2, Remote 2 temperature LSBs. [5:4] LTMP, Local temperature LSBs. [3:2] TDM1, Remote 1 temperature LSBs.
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 (0x73) turns averaging off. The default round robin cycle time takes 146.5 ms. Table 12. Conversion Time with Averaging Disabled
Channel Voltage Channels Remote Temperature 1 Remote Temperature 2 Local Temperature Measurement Time (ms) 0.7 7 7 1.3
Temperature Limit Registers
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 (depending on the way the interrupt mask register is programmed and assuming that SMBALERT is set as an output on the appropriate pin). Register 0x4E, Remote 1 Temperature Low Limit = 0x81 default Register 0x4F, Remote 1 Temperature High Limit = 0x7F default Register 0x50, Local Temperature Low Limit = 0x81 default Register 0x51, Local Temperature High Limit = 0x7F default Register 0x52, Remote 2 Temperature Low Limit = 0x81 default Register 0x53, Remote 2 Temperature High Limit = 0x7F default
When Bit 7 of Configuration Register 6 (0x10) is set, the default round robin cycle time increases to 240 ms. Table 13. Conversion Time with Averaging Enabled
Channel Voltage Channels Remote Temperature Local Temperature Measurement Time (ms) 11 39 12
Single-Channel ADC Conversions
Setting Bit 6 of Configuration Register 2 (0x73) places the ADT7476A into single-channel ADC conversion mode. In this mode, the ADT7476A 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 14. Programming Single Channel ADC Mode for Temperatures
Bits [7:5] Reg. 0x55 101 110 111 Channel Selected Remote 1 temperature Local temperature Remote 2 temperature
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ADT7476A
Configuration Register 2 (0x73)
[4] = 1, averaging off. [6] = 1, single-channel convert mode.
THERM LIMIT
HYSTERESIS (C) TEMPERATURE
TACH1 Minimum High Byte (0x55)
[7:5] selects ADC channel for single-channel convert mode.
Overtemperature Events
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 (Register 0x38, Register 0x39, and Register 0x3A). This effectively runs the fans at the fastest allowed speed. The fans run at this speed until the temperature drops below THERM minus hysteresis. This can be disabled by setting Bit 2, the boost bit, in Configuration Register 3 (0x78). The hysteresis value for the THERM temperature limit is the value programmed into the hysteresis registers (0x6D and 0x6E). The default hysteresis value is 4C.
Figure 28. THERM Temperature Limit Operation
THERM can be disabled on specific temperature channels using Bits [7:5] of Configuration Register 5 (0x7C). THERM can also be disabled by:
*
*
Writing -64C to the appropriate THERM temperature limit in Offset 64 mode. Writing -128C to the appropriate THERM temperature limit in twos complement mode.
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05742-029
FANS
100%
ADT7476A LIMITS, STATUS REGISTERS, AND INTERRUPTS
LIMIT VALUES
Associated with each measurement channel on the ADT7476A 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 is detected by polling the device. Alternatively, SMBALERT interrupts can be generated to flag out-of-limit conditions to a processor or microcontroller.
16-Bit Limits
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.
8-Bit Limits
The following is a list of 8-bit limits on the ADT7476A. Voltage Limit Registers Register 0x44, 2.5 V Low Limit = 0x00 default Register 0x45, 2.5 V High Limit = 0xFF default Register 0x46, VCCP Low Limit = 0x00 default Register 0x47, VCCP High Limit = 0xFF default Register 0x48, VCC Low Limit = 0x00 default Register 0x49, VCC High Limit = 0xFF default Register 0x4A, 5 V Low Limit = 0x00 default Register 0x4B, 5 V High Limit = 0xFF default Register 0x4C, 12 V Low Limit = 0x00 default Register 0x4D, 12 V High Limit = 0xFF default Temperature Limit Registers Register 0x4E, Remote 1 Temperature Low Limit = 0x81 default Register 0x4F, Remote 1 Temperature High Limit = 0x7F default Register 0x6A, Remote 1 THERM Limit = 0x64 default Register 0x50, Local Temperature Low Limit = 0x81 default Register 0x51, Local Temperature High Limit = 0x7F default Register 0x6B, Local THERM Limit = 0x64 default Register 0x52, Remote 2 Temperature Low Limit = 0x81 default Register 0x53, Remote 2 Temperature High Limit = 0x7F default Register 0x6C, Remote 2 THERM Limit = 0x64 default THERM Timer Limit Register Register 0x7A, THERM Timer Limit = 0x00 default.
Fan Limit Registers
Register 0x54, TACH1 Minimum Low Byte = 0xFF default Register 0x55, TACH1 Minimum High Byte = 0xFF default Register 0x56, TACH2 Minimum Low Byte = 0xFF default Register 0x57, TACH2 Minimum High Byte = 0xFF default Register 0x58, TACH3 Minimum Low Byte = 0xFF default Register 0x59, TACH3 Minimum High Byte = 0xFF default Register 0x5A, TACH4 Minimum Low Byte = 0xFF default Register 0x5B, TACH4 Minimum High Byte = 0xFF default
Out-of-Limit Comparisons
Once all limits have been programmed, the ADT7476A can be enabled for monitoring. The ADT7476A 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 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 (0x40). 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. 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.
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ADT7476A
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
Interrupt Status Register 1 (0x41)
Bit 7 (OOL) = 1, denotes a bit in Interrupt Status Register 2 is set and Interrupt 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. If the 2.5 V input is configured as THERM, this bit represents the status of THERM.
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.
Interrupt Status Register 2 (0x42)
STATUS REGISTERS
The results of limit comparisons are stored in Interrupt Status Register 1 and Interrupt Status Register 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 Interrupt Status Register 1 (0x41), 1 means an out-of-limit event has been flagged in Interrupt Status Register 2. This means the user also needs to read Interrupt 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 out-of-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 mask registers (0x74 and 0x75) allow individual interrupt sources to be masked from causing an SMBALERT. However, if one of these masked interrupt sources goes out of limit, its associated status bit is set in the status registers.
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. Alternatively, indicates the status of GPIO6. 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 VID4 inputs.
SMBALERT Interrupt Behavior
The ADT7476A 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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ADT7476A
Masking Interrupt Sources
HIGH LIMIT
TEMPERATURE
STICKY STATUS BIT TEMP BACK IN LIMIT (STATUS BIT STAYS SET) SMBALERT
CLEARED ON READ (TEMP BELOW LIMIT)
Interrupt Mask Register 1 (0x74) and Interrupt Mask Register 2 (0x75) allow individual interrupt sources to be masked to prevent SMBALERT interrupts. Note: Masking an interrupt source prevents only the SMBALERT output from being asserted; the appropriate status bit is set normally.
05742-030
HIGH LIMIT
Figure 29. SMBALERT and Status Bit Behavior
TEMPERATURE
Figure 29 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 the software is periodically polling the device. 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. THERM overtemperature events are not sticky. They reset immediately after the overtemperature condition ceases.
CLEARED ON READ (TEMP BELOW LIMIT) STICKY STATUS BIT TEMP BACK IN LIMIT (STATUS BIT STAYS SET) SMBALERT INTERRUPT MASK BIT SET INTERRUPT MASK BIT CLEARED (SMBALERT REARMED)
05742-031
Figure 30. How Masking the Interrupt Source Affects SMBALERT Output
Interrupt Mask Register 1 (0x74)
Bit 7 (OOL) = 1, masks SMBALERT for any alert condition flagged in Interrupt 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 1 (VCCP) = 1, masks SMBALERT for VCCP channel. Bit 0 (2.5V) = 1, masks SMBALERT for 2.5VIN/THERM.
*
Handling SMBALERT Interrupts
To prevent the system from being tied up servicing interrupts, it is recommend to handle the SMBALERT interrupt as follows: 1. 2. 3. 4. 5. 6. 7. 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 (0x74 and 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 30.
Interrupt Mask Register 2 (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. If the TACH4 pin is being used as the THERM input, this bit masks SMBALERT for a THERM event. If the TACH4 pin is being used as GPIO6, setting this bit masks interrupts related to GPIO6.
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ADT7476A
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. When the THERM pin is driven low externally, the user can also set up the ADT7476A to run the fans at 100%. The fans run at 100% for the duration of time that the THERM pin is pulled low. This is done by setting the BOOST bit (Bit 2) in Configuration Register 3 (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 below TMIN or if the duty cycle in manual mode is set to 0x00, pulling the THERM low externally has no effect. See Figure 31 for more information.
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 15. Configuring Pin 10 as SMBALERT Output
Register Configuration Register 3 (0x78) Bit Setting [1] Pin 10 = SMBALERT [0] Pin 10 = PWM2
TMIN
THERM
Assigning THERM Functionality to a Pin
Pin 14 on the ADT7476A has four possible functions: SMBALERT, THERM, GPIO6, and TACH4. The user chooses the required functionality by setting Bit 0 and Bit 1 of Configuration Register 4 (0x7D). If THERM is enabled on Bit 1, Configuration Register 3 (0x78): * * Pin 22 becomes THERM. If Pin 14 is configured as THERM on Bit 0 and Bit 1 of Configuration Register 4 (0x7D), THERM is enabled on this pin.
THERM ASSERTED TO LOW AS AN INPUT: FANS DO NOT GO TO 100% BECAUSE TEMPERATURE IS BELOW TMIN.
05742-032
THERM ASSERTED TO LOW AS AN INPUT: FANS DO NOT GO TO 100% BECAUSE TEMPERATURE IS ABOVE TMIN AND FANS ARE ALREADY RUNNING.
Figure 31. Asserting THERM Low as an Input in Automatic Fan Speed Control Mode
THERM TIMER
The ADT7476A 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 ADT7476A's THERM input and stopped when THERM is de-asserted. 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 (where it is cleared), or until it reaches full scale. If the counter reaches full scale, it stops at that reading until cleared. The 8-bit THERM timer status register (0x79) is designed so 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 32).
If THERM is not enabled: * * Pin 22 becomes a 2.5 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 GPIO6
Table 16. 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.
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ADT7476A
THERM
2.
00000001 76543210 THERM ASSERTED 22.76ms
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 register (0x7A) = 0x00, the F4P bit is set.
THERM TIMER (REG. 0x79)
3. 4.
THERM
ACCUMULATE THERM LOW ASSERTION TIMES THERM TIMER (REG. 0x79) 00000010 76543210 THERM ASSERTED 45.52ms
Generating SMBALERT Interrupts from THERM Timer Events
The ADT7476A 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 sec (first THERM assertion) to 5.825 sec 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 Interrupt Status Register 2 is set and an SMBALERT is generated. Note: Depending on which pins are configured as a THERM timer, setting the F4P bit (Bit 5) of Mask Register 2 (0x75) or Bit 0 of Mask Register 1 (0x74) masks out SMBALERT; although the F4P bit of Interrupt Status Register 2 is still set if the THERM timer limit is exceeded. Figure 33 is a functional block diagram of the THERM timer, limit, and associated circuitry. Writing a value of 0x00 to the THERM timer limit register (0x7A) causes an 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.
2.914s 1.457s 728.32ms 364.16ms THERM TIMER (REG. 0x79) 182.08ms 91.04ms 45.52ms 22.76ms
THERM
ACCUMULATE THERM LOW ASSERTION TIMES THERM TIMER (REG. 0x79) 00000101 7 6 5 4 3 2 1 0 THERM ASSERTED 113.8ms (91.04ms + 22.76ms)
Figure 32. Understanding the THERM Timer
When using the THERM timer, be aware of the following: After a THERM timer read (0x79) 1. 2. The contents of the timer are cleared on read. The F4P bit (Bit 5) of Interrupt Status Register 2 needs to be cleared (assuming that the THERM timer limit has been exceeded).
If the THERM timer is read during a THERM assertion, the following occurs: 1. The contents of the timer are cleared.
THERM LIMIT (REG. 0x7A)
2.914s 1.457s 728.32ms 364.16ms 182.08ms 91.04ms 45.52ms 22.76ms
01234567
05742-033
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
05742-034
F4P BIT (BIT 5) MASK REGISTER 2 (REG. 0x75)
Figure 33. Functional Block Diagram of THERM Monitoring Circuitry
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ADT7476A
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 (0x78) enables the THERM timer monitoring functionality. This is disabled on Pin 14 and Pin 22 by default. Setting Bit 0 and Bit 1 (PIN14FUNC) of Configuration Register 4 (0x7D) enables THERM timer output functionality on Pin 22 (Bit 1 of Configuration Register 3, THERM, must also be set). Pin 14 can also be used as TACH4. 2. Select the desired fan behavior for THERM timer events. Assuming the fans are running, setting Bit 2 (BOOST bit) of Configuration Register 3 (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, then the fans do not run to full speed. 3. Select whether THERM timer events should generate SMBALERT interrupts. Setting Bit 5 (F4P) of Mask Register 2 (0x75) or Bit 0 of Mask Register 1 (0x74), depending on which pins are configured as a THERM timer, masks 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 if only a cumulative THERM assertion time limit is exceeded. A value of 0x00 causes an SMBALERT to be generated on the first THERM assertion. 5. Select a THERM monitoring time.
THERM
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 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 sec to be exceeded, and the next time it takes only 1 hour, then a serious degradation in system performance has occurred.
Configuring the THERM Pin as an Output
In addition to monitoring THERM as an input, the ADT7476A can optionally drive THERM low as an output. When 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 Register 0x6A, Register 0x6B, and Register 0x6C, respectively. Setting Bits [5:7] of Configuration Register 5 (0x7C) enables the THERM output feature for the Remote 1, local, and Remote 2 temperature channels, respectively. Figure 34 shows how the THERM pin asserts low as an output in the event of a critical overtemperature.
THERM LIMIT 0.25C THERM LIMIT
TEMP
This value specifies how often OS- or BIOS-level software checks the THERM timer. For example, BIOS can 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, system performance is degrading significantly because THERM is asserting more frequently on an hourly basis.
MONITORING CYCLE
Figure 34. Asserting THERM as an Output, Based on Tripping THERM Limits
An alternative method of disabling THERM is to program the THERM temperature limit to -63C 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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05742-035
ADT7476A
Enabling and Disabling THERM on individual Channels
THERM can be enabled/disabled for individual or combinations of temperature channels using Bits [7:5] of Configuration Register 5 (0x7C). Typical notebook fans draw a nominal 170 mA, so SOT devices can be used where board space is a concern. In desktops, fans 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 output pin. The MOSFET should also have a low on resistance to ensure that there is not a 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 35 shows how to drive a 3-wire fan using PWM control.
12V 12V
THERM Hysteresis
Setting Bit 0 of Configuration Register 7 (0x11) disables THERM hysteresis. If THERM hysteresis is enabled and THERM is disabled (Bit 2 of Configuration Register 4, 0x7D), the THERM pin does not assert low when a THERM event occurs. If THERM hysteresis is disabled and THERM is disabled (Bit 2 of Configuration Register 4, 0x7D) and assuming the appropriate pin is configured as THERM), the THERM pin asserts low when a THERM event occurs. If THERM and THERM hysteresis are both enabled, the THERM output asserts as expected.
10k TACH 10k 4.7k TACH 12V FAN 1N4148
ADT7476A
3.3V 10k
05742-036
THERM Operation in Manual Mode
In manual mode, THERM events do not cause fans to go to full speed, unless Bit 3 of Configuration Register 6 (0x10) is set to 1. Additionally, Bit 3 of Configuration Register 4 (0x7D) can be used to select the PWM speed on a THERM event (100% or maximum PWM). Bit 2 in Configuration Register 4 (0x7D) can be set to disable THERM events from affecting the fans.
PWM
Q1 NDT3055L
Figure 35. Driving a 3-Wire Fan Using an N-Channel MOSFET
Figure 35 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 5.5 V maximum to prevent damaging the ADT7476A. Figure 36 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 so that the transistor is saturated when the fan is powered on. Because the fan drive circuitry in 4-wire fans is not switched on or off, as with previous PWM driven/powered fans, the internal drive circuit is always on and uses the PWM input as a signal instead of a power supply. This enables the internal fan drive circuit to perform better than 3-wire fans, especially for high frequency applications.
12V 10k TACH 10k 4.7k TACH 12V FAN 1N4148 12V
FAN DRIVE USING PWM CONTROL
The ADT7476A 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 ADT7476A PWM frequency can be set to a selection of low frequencies or a single high PWM frequency. The low frequency options are used for 3-wire fans, while the high frequency option is usually used with 4-wire fans. For 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.
ADT7476A
3.3V 470
05742-037
PWM
Q1 MMBT2222
Figure 36. Driving a 3-Wire Fan Using an NPN Transistor
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ADT7476A
Figure 37 shows a typical drive circuit for 4-wire fans.
12V 12V 12V, 4-WIRE FAN 10k TACH 10k 4.7k TACH VCC TACH PWM
Because the MOSFET can handle up to 3.5 A, users can connect 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 outputs are not required to source current, and that they sink less than the 5 mA maximum current specified on the data sheet.
ADT7476A
3.3V 2k
Driving up to Three Fans from PWM3
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 38 and Figure 39. The SYNC bit in Register 0x62 enables this function. Synchronization is not required in high frequency mode when used with 4-wire fans.
05742-038
PWM
Figure 37. Driving a 4-Wire Fan
Driving Two Fans from PWM3
The ADT7476A 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 38 shows how to drive two fans in parallel using low cost NPN transistors. Figure 39 shows the equivalent circuit using a MOSFET.
(SYNC) Enhance Acoustics Register 1 (0x62)
[4] SYNC = 1, synchronizes TACH2, TACH3, and TACH4 to PWM3. .
12V
ADT7476A
3.3V
3.3V TACH3
1N4148
TACH4 3.3V
1k PWM3 2.2k
3.3V Q1 MMBT3904 10k
Q2 MMBT2222
10k Q3 MMBT2222
05742-039
Figure 38. Interfacing Two Fans in Parallel to the PWM3 Output Using Low Cost NPN Transistors
3.3V 10k TYPICAL TACH4 3.3V 3.3V +V +V
ADT7476A
TACH3
10k TYPICAL TACH 3.3V 3.3V 10k TYPICAL 5V OR 12V FAN 1N4148 TACH 5V OR 12V FAN
PWM3
Figure 39. Interfacing Two Fans in Parallel to the PWM3 Output Using a Single N-Channel MOSFET
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05742-040
Q1 NDT3055L
ADT7476A
LAYING OUT 3-WIRE FANS
Figure 40 shows how to lay out a common circuit arrangement for 3-wire fans.
12V OR 5V R1
12V VCC
PULL-UP 4.7k TYPICAL
TACH OUTPUT
TACH ZD1*
FAN SPEED COUNTER
05742-043
05742-045
05742-044
1N4148 3.3V OR 5V
ADT7476A
*CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8 x VCC
R2
R4 PWM
Figure 42. Fan with TACH Pull-Up to Voltage > 5.5V, (for Example, 12 V) Clamped with Zener Diode
TACH R3
Figure 40. Planning for 3-Wire Fans on a PCB
05742-041
Q1 MMBT2222
If the fan has a strong pull-up (less than 1 k) to 12 V or a totem-pole output, a series resistor can be added to limit the Zener current, as shown in Figure 43.
5V OR 12V FAN PULL-UP TYP <1k OR TOTEM POLE VCC
TACH Inputs
Pin 9, Pin 11, Pin 12, and Pin 14 (when configured as TACH inputs) are high impedance inputs intended for fan speed measurement. Signal conditioning in the ADT7476A accommodates the slow rise and fall times typical of fan tachometer outputs. The maximum input signal range is 0 V to 5.5 V, even though VCC is 3.3 V. In the event that these inputs are supplied from fan outputs that exceed 0 V to 5.5 V, either resistive attenuation of the fan signal or diode clamping must be included to keep inputs within an acceptable range. Figure 41 to Figure 44 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 41.
VCC 12V
R1 10k TACH OUTPUT
TACH ZD1 ZENER*
FAN SPEED COUNTER
ADT7476A
*CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8 x VCC
Figure 43. Fan with Strong TACH Pull-Up to > VCC or Totem-Pole Output, Clamped with Zener Diode and Resistor
Alternatively, a resistive attenuator can be used, as shown in Figure 44. R1 and R2 should be chosen such that 2 V < VPULL-UP x R2 / (RPULL-UP + R1 + R2) < 5.5 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 are 100 k and 40 k, respectively. This gives a high input voltage of 3.42 V.
12V VCC
PULL-UP 4.7k TYP TACH OUTPUT TACH
FAN SPEED COUNTER
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ADT7476A
<1k R1* TACH OUTPUT TACH R2* FAN SPEED COUNTER
Figure 41. Fan with TACH Pull-Up to VCC
If the fan output has a resistive pull-up to 12 V, or other voltage greater than 5.5 V, the fan output can be clamped with a Zener diode, as shown in Figure 42. The Zener diode voltage should be chosen so that it is greater than VIH of the TACH input but less than 5.5 V, allowing for the voltage tolerance of the Zener. A value between 5 V and 5.5 V is suitable.
ADT7476A
*SEE TEXT
Figure 44. Fan with Strong TACH Pull-Up to > VCC or Totem-Pole Output, Attenuated with R1/R2
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ADT7476A
The fan counter does not count the fan TACH output pulses directly because the fan speed could be less than 1000 RPM, and it takes 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 45), 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 TACH pulses per revolution register (0x7B). This register contains two bits for each fan, allowing one, two (default), three, or four TACH pulses to be 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 that either the fan has stalled or is running very slowly (<100 RPM). High Limit: > Comparison Performed 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. Measuring fan TACH has the following caveat: When the ADT7476A starts up, TACH measurements are locked. In effect, an internal read of the low byte has been made for each TACH input. The net result of this is that all TACH readings are locked until the high byte is read from the corresponding TACH registers. All TACH-related interrupts are also ignored until the appropriate high byte is read. Once the corresponding high byte has been read, TACH measurements are unlocked and interrupts are processed as normal.
2 3 4
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CLOCK
PWM
TACH
1
Fan TACH Limit Registers
The fan TACH limit registers are 16-bit values consisting of two bytes. Register 0x54, TACH1 Minimum Low Byte = 0xFF default Register 0x55, TACH1 Minimum High Byte = 0xFF default Register 0x56, TACH2 Minimum Low Byte = 0xFF default Register 0x57, TACH2 Minimum High Byte = 0xFF default Register 0x58, TACH3 Minimum Low Byte = 0xFF default Register 0x59, TACH3 Minimum High Byte = 0xFF default Register 0x5A, TACH4 Minimum Low Byte = 0xFF default Register 0x5B, TACH4 Minimum High Byte = 0xFF default
Figure 45. Fan Speed Measurement
Fan TachometerReading Registers
The fan tachometer readings are 16-bit values consisting of a 2-byte read from the ADT7476A. Register 0x28, TACH1 Low Byte = 0x00 default Register 0x29, TACH1 High Byte = 0x00 default Register 0x2A, TACH2 Low Byte = 0x00 default Register 0x2B, TACH2 High Byte = 0x00 default Register 0x2C, TACH3 Low Byte = 0x00 default Register 0x2D, TACH3 High Byte = 0x00 default Register 0x2E, TACH4 Low Byte = 0x00 default Register 0x2F, TACH4 High Byte = 0x00 default
Fan Speed Measurement Rate
The fan TACH readings are normally updated once every second. When set, the FAST bit (Bit 3) of Configuration Register 3 (0x78) updates the fan TACH readings every 250 ms.
Reading Fan Speed from the ADT7476A
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 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).
DC Bits
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. Once high frequency mode is enabled in 4-wire fans, the dc bits do not need to be set because this is automatically done internally.
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ADT7476A
Calculating Fan Speed
Assuming a fan with two pulses per revolution, and with the ADT7476A programmed to measure two pulses per revolution, 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: TACH1 High Byte (0x29) = 0x17 TACH1 Low Byte (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 = (90,000 x 60)/6143 Fan Speed = 879 RPM inertia and is quieter on spin-up than fans that are programmed to spin up for a given time.
Fan Startup Timeout
To prevent the generation of false interrupts as a fan spins up (because it is below running speed), the ADT7476A includes a fan startup timeout function. During this time, the ADT7476A looks for two TACH pulses. If two TACH pulses are not detected, an interrupt is generated. Fan startup timeout can be disabled by setting Bit 5 (FSPDIS) of Configuration Register 1 (0x40).
PWM1, PWM2, PWM3 Configuration (0x5C, 0x5D, 0x5E)
[2:0] SPIN, startup timeout for PWM1 = 0x5C, PWM2 = 0x5D, and PWM3 = 0x5E. 000 = No startup timeout 001 = 100 ms 010 = 250 ms default 011 = 400 ms 100 = 667 ms 101 = 1 sec 110 = 2 sec 111 = 4 sec
TACH Pulses per Revolution
Different fan models can output either one, two, three, or four TACH pulses per revolution. Once the number of fan TACH pulses has been determined, it can be programmed into the TACH Pulses per Revolution Register (0x7B) for each fan. Alternatively, this register can be used to determine the number of pulses per revolution output by a given fan. By plotting fan speed measurements at 100% speed with different pulses per revolution settings, the smoothest graph with the lowest ripple determines the correct pulses per revolution value.
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 (0x40) disables the spin-up for two TACH pulses. Instead, the fan spins up for the fixed time as selected in Register 0x5C to Register 0x5E.
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. [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.
PWM Logic State
The PWM outputs can be programmed high for 100% duty cycle (noninverted) or low for 100% duty cycle (inverted).
PWM1 Configuration (0x5C)
[4] INV. 0 = Logic high for 100% PWM duty cycle 1 = Logic low for 100% PWM duty cycle
Fan Spin-Up
The ADT7476A 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%. Fans have different spin-up characteristics and take different times to overcome inertia. The advantage of the ADT7476A is that it runs the fans just fast enough to overcome
PWM2 Configuration (0x5D)
[4] INV. 0 = Logic high for 100% PWM duty cycle 1 = Logic low for 100% PWM duty cycle
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ADT7476A
PWM3 Configuration (0x5E)
[4] INV. 0 = Logic high for 100% PWM duty cycle 1 = Logic low for 100% PWM duty cycle
PWM Configuration Registers (0x5C to 0x5E)
[7:5] BHVR. 111 = manual mode Once under manual control, each PWM output can be manually updated by writing to Register 0x30 to Register 0x32 (PWM current duty cycle registers).
Low Frequency Mode PWM Drive Frequency
The PWM drive frequency can be adjusted for the application. Register 0x5F to Register 0x61 configure the PWM frequency for PWM1 to PWM3, respectively.
Programming the PWM Current Duty Cycle Registers
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%, Value (decimal) = 33/0.39 = 85 (decimal) Value = 85 (decimal) or 0x54 (hex)
PWM1, PWM 2, PWM3 Frequency Registers (0x5F to 0x61)
[2:0] FREQ 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
High Frequency Mode PWM Drive
Setting Bit 3 of Register 0x5F, Register 0x60, and Register 0x61 enables high frequency mode for Fan1, Fan 2, and Fan 3 respectively. In high frequency mode, the PWM drive frequency is always 22.5 kHz. When high frequency mode is enabled, the dc bits are automatically asserted internally and do not need to be changed.
PWM Current Duty Cycle Registers
Register 0x30 PWM1 Current Duty Cycle = 0xFF (100% default) Register 0x31 PWM2 Current Duty Cycle = 0xFF (100% default) Register 0x32 PWM3 Current Duty Cycle = 0xFF (100% 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.
Fan Speed Control
The ADT7476A controls fan speed using automatic and manual modes: * 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. In manual fan speed control mode, the ADT7476A allows the duty cycle of any PWM output to be adjusted manually. 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 Register 0x5C to Register 0x5E (PWM Configuration) control the behavior of each PWM output.
PROGRAMMING TRANGE
TRANGE defines the distance between TMIN and 100% PWM. For the ADT7467, ADT7468 and ADT7473, TRANGE is effectively a slope. For the ADT7475 andADT7476A, TRANGE is no longer a slope, but defines the temperature region where the PWM output linearly ramps from PWMMIN to 100% PWM.
PWM = 100% PWMMAX
*
TRANGE PWM = 0% TMIN
Figure 46. TRANGE
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05742-047
PWMMIN
ADT7476A PROGRAMMING THE AUTOMATIC FAN SPEED CONTROL LOOP
To understand the automatic fan speed control loop more efficiently, it is recommended to use the ADT7476A 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 system development process. The ADT7476A 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 current consumption. The automatic fan speed control mode is very flexible due 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 47 gives a top-level overview of the automatic fan control circuitry on the ADT7476A. 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 ADT7476A 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, designers 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 47 shows fan-specific controls. 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.
MANUAL FAN CONTROL OVERVIEW
In unusual circumstances, it can be necessary to manually control the speed of the fans. Because the ADT7476A has an SMBus interface, a system can read back all necessary voltage, fan speed, and temperature information, and use this information to control the speed of the fans by writing to the PWM current duty cycle register (0x30, 0x31, and 0x32) of the appropriate fan. Bits [7:5] of the PWMx configuration registers (0x5C, 0x5D, 0x5E) are used to set fans up for manual control.
THERM OPERATION IN MANUAL MODE
In manual mode, if the temperature increases above the programmed THERM temperature limit, the fans automatically speed up to maximum PWM or100% PWM, whichever way the appropriate fan channel is configured.
AUTOMATIC FAN CONTROL OVERVIEW
The ADT7476A can automatically control the speed of fans based on the measured temperature. This is done independently of CPU intervention once initial parameters are set up.
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ADT7476A
THERMAL CALIBRATION 100% PWM MIN PWM CONFIG PWM GENERATOR 0% PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT) PWM1
REMOTE 1 TEMP
TMIN
TRANGE
TACHOMETER 1 MEASUREMENT PWM CONFIG PWM GENERATOR RAMP CONTROL (ACOUSTIC ENHANCEMENT)
TACH1
THERMAL CALIBRATION
100%
MUX
0% PWM MIN
PWM2
LOCAL TEMP
TMIN
TRANGE
TACHOMETER 2 MEASUREMENT PWM CONFIG PWM GENERATOR RAMP CONTROL (ACOUSTIC ENHANCEMENT)
TACH2
THERMAL CALIBRATION
100%
PWM3
Figure 47. Automatic Fan Control Block Diagram
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05742-048
REMOTE 2 TEMP
TMIN
TRANGE
0%
TACHOMETER 3 AND 4 MEASUREMENT
TACH3
ADT7476A
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 ADT7476A functionality is used? * * * * PWM2 or SMBALERT? TACH4 fan speed measurement or overtemperature THERM function? 2.5 V voltage monitoring or overtemperature THERM function? 12 V voltage monitoring or VID5 input? 4. 2. How many fans are 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 ADT7476A, or will the CPU fan 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 ADT7476A be physically located in the system? This influences the assignment of the temperature measurement channels to particular system thermal zones. For example, locating the ADT7476A close to the VRM controller circuitry allows the VRM temperature to be monitored using the local temperature channel.
3.
The ADT7476A 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
PWM CONFIG PWM GENERATOR RAMP CONTROL (ACOUSTIC ENHANCEMENT) PWM1
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0% PWM MIN
TACHOMETER 1 MEASUREMENT PWM CONFIG PWM GENERATOR RAMP CONTROL (ACOUSTIC ENHANCEMENT)
TACH1 CPU FAN SINK
THERMAL CALIBRATION
100%
MUX
0% PWM MIN
PWM2
TMIN LOCAL = VRM TEMP
TRANGE
TACHOMETER 2 MEASUREMENT PWM CONFIG PWM GENERATOR RAMP CONTROL (ACOUSTIC ENHANCEMENT)
TACH2
THERMAL CALIBRATION
100%
FRONT CHASSIS PWM3
TMIN REMOTE 2 = CPU TEMP
TRANGE
0%
TACHOMETER 3 AND 4 MEASUREMENT
TACH3
REAR CHASSIS
Figure 48. Hardware Configuration Example
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ADT7476A
Recommended Implementation 1
Configuring the ADT7476A as shown in Figure 49 provides the system designer with the following features: * * * * * * Six VID inputs (VID0, VID1, VID2, VID3, VID4, and VID6) 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. * * * * * * 5 V measurement input. VRM temperature using local temperature sensor. CPU temperature measured using the Remote 1 temperature channel. Ambient temperature measured through the Remote 2 temperature channel. If not using VID5, it can be reconfigured as the 12 V monitoring input. 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. SMBALERT system interrupt output.
*
FRONT CHASSIS FAN
ADT7476A
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- VCC +5VIN +12VIN/VID5 GND
SDA SCL SMBALERT
05742-050
ICH
Figure 49. Recommended Implementation 1
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ADT7476A
Recommended Implementation 2
Configuring the ADT7476A as shown in Figure 50 provides the system designer with the following features: * * * * * * Six VID inputs (VID0, VID1, VID2, VID3, VID4, and VID6) 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. * * * * * * 5 V measurement input. VRM temperature using local temperature sensor. CPU temperature measured using the Remote 1 temperature channel. Ambient temperature measured through the Remote 2 temperature channel. If not using VID5, it can be reconfigured as the 12 V monitoring input. Bidirectional THERM pin allows the monitoring of PROCHOT output/input from an Intel P4 processor, for example, or can be used as an overtemperature THERM output.
FRONT CHASSIS FAN
ADT7476A
TACH2 PWM2 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- SDA VCC +5VIN +12VIN/VID5 GND ICH SCL
CPU
Figure 50. Recommended Implementation 2
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05742-051
ADT7476A
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, manually (under software control), or 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 Register 0x5C, Register 0x5D, and Register 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. 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), Register 0x5C, Register 0x5D, Register 0x5E. 011 = PWMx runs full speed 100 = PWMx disabled (default) 111 = Manual mode. PWMx is running under software control. In this mode, PWM current duty cycle registers (0x30 to 0x32) are writable and control the PWM outputs.
Automatic Fan Control Mux Options
[7:5] (BHVR), Register 0x5C, Register 0x5D, Register 0x5E. 000 = Remote 1 temperature controls PWMx 001 = Local temperature controls PWMx 010 = Remote 2 temperature controls PWMx
MUX
THERMAL CALIBRATION
100%
PWM MIN
PWM CONFIG PWM GENERATOR RAMP CONTROL (ACOUSTIC ENHANCEMENT) PWM1
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0% PWM MIN
TACHOMETER 1 MEASUREMENT PWM CONFIG PWM GENERATOR RAMP CONTROL (ACOUSTIC ENHANCEMENT)
TACH1 CPU FAN SINK
THERMAL CALIBRATION
100%
MUX
0% PWM MIN
PWM2
TMIN LOCAL = VRM TEMP
TRANGE
TACHOMETER 2 MEASUREMENT PWM CONFIG PWM GENERATOR RAMP CONTROL (ACOUSTIC ENHANCEMENT)
TACH2
THERMAL CALIBRATION
100%
FRONT CHASSIS PWM3
TMIN REMOTE 2 = CPU TEMP
TRANGE
0%
TACHOMETER 3 AND 4 MEASUREMENT
TACH3
REAR CHASSIS
Figure 51. Assigning Temperature Channels to Fan Channels
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05742-052
ADT7476A
Mux Configuration Example
This is an example of how to configure the mux in a system using the ADT7476A 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).
Example Mux Settings
[7:5] (BHVR), PWM1 Configuration Register (0x5C). 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 52.
* *
THERMAL CALIBRATION
100%
PWM MIN
PWM CONFIG PWM GENERATOR RAMP CONTROL (ACOUSTIC ENHANCEMENT) PWM1
TMIN REMOTE 2 = CPU TEMP
TRANGE
0%
THERMAL CALIBRATION
MUX
100%
PWM MIN
TACHOMETER 1 MEASUREMENT PWM CONFIG PWM GENERATOR RAMP CONTROL (ACOUSTIC ENHANCEMENT)
TACH1 CPU FAN SINK
PWM2
TMIN LOCAL = VRM TEMP
TRANGE
0% PWM MIN
TACHOMETER 2 MEASUREMENT PWM CONFIG PWM GENERATOR RAMP CONTROL (ACOUSTIC ENHANCEMENT)
TACH2
THERMAL CALIBRATION
100%
FRONT CHASSIS PWM3
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0%
TACHOMETER 3 AND 4 MEASUREMENT
TACH3
REAR CHASSIS
Figure 52. Mux Configuration Example
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05742-053
ADT7476A
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, which can be programmed in 1C increments. A TMIN register is associated with each temperature measurement channel: Remote 1, local, and Remote 2 temperature. 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 psycho-acoustic reasons, it is desirable that the fan never switch off below TMIN. Setting Bits [7:5] of Enhance Acoustics Register 1 (0x62) keeps the fans running at the PWM minimum duty cycle if the temperature should fall below TMIN.
100%
TMIN Registers
Register 0x67, Remote 1 Temperature TMIN = 0x5A (90C) Register 0x68, Local Temperature TMIN = 0x5A (90C) Register 0x69, Remote 2 Temperature TMIN = 0x5A (90C)
Enhance Acoustics Register 1 (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.
PWM DUTYCYCLE
0% TMIN
THERMAL CALIBRATION
100%
PWM MIN
PWM CONFIG PWM GENERATOR RAMP CONTROL (ACOUSTIC ENHANCEMENT) PWM1
TMIN REMOTE 2 = CPU TEMP
TRANGE
0% PWM MIN TACHOMETER 1 MEASUREMENT PWM CONFIG PWM GENERATOR RAMP CONTROL (ACOUSTIC ENHANCEMENT) PWM2 TACH1 CPU FAN SINK
THERMAL CALIBRATION
100%
MUX
0% PWM MIN
TMIN LOCAL = VRM TEMP
TRANGE
TACHOMETER 2 MEASUREMENT PWM CONFIG PWM GENERATOR RAMP CONTROL (ACOUSTIC ENHANCEMENT)
TACH2
THERMAL CALIBRATION
100%
FRONT CHASSIS PWM3
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0%
TACHOMETER 3 AND 4 MEASUREMENT
TACH3
REAR CHASSIS
Figure 53. Understanding the TMIN Parameter
Rev. 0 | Page 42 of 72
05742-054
ADT7476A
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
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%, Value (decimal) = 33/0.39 = 85 (decimal) Value = 85 (decimal)l or 54 (hex)
PWM Minimum Duty Cycle Registers
Register 0x64, PWM1 Minimum Duty Cycle = 0x80 (50% default)
PWMMIN 0%
05742-055
Register 0x65, PWM2 Minimum Duty Cycle = 0x80 (50% default) Register 0x66, PWM3 Minimum Duty Cycle = 0x80 (50% default)
TMIN TEMPERATURE
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
% Fan Speed = PWM Duty Cycle x 10
Figure 54. 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, 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 55 illustrates this as PWM1MIN (front fan), which is turned on at a minimum duty cycle of 20%, while PWM2MIN (rear fan) turns on at a minimum of 40% duty cycle. Note: Both fans turn on at exactly the same temperature, defined by TMIN.
100%
STEP 5--PWMMAX FOR PWM (FAN) OUTPUTS
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 has no effect unless it is programmed.
PWM DUTY CYCLE
M2 PW
PWM2MIN PWM1MIN 0%
05742-056
PW
M1
TMIN
TEMPERATURE
100%
PWM DUTY CYCLE
Figure 55. Operating Two Different Fans from a Single Temperature Channel
PWMMAX
Programming the PWM Minimum Duty Cycle Registers
The PWM minimum duty cycle 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%.
PWMMIN 0%
05742-057
TMIN
TEMPERATURE
Figure 56. PWMMAX Determines Maximum PWM Duty Cycle Below the THERM Temperature Limit
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ADT7476A
Programming the PWM Maximum Duty Cycle Registers
The PWM maximum duty cycle 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%. The value to be programmed into the PWM maximum duty cycle register is given by Value (decimal) = PWMMAX/0.39 Example 1: For a maximum 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 75%, Value (decimal) = 75/0.39 = 85 (decimal) Value = 192 (decimal) or C0 (hex)
100%
The TRANGE 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 ADT7476A evaluation software, you can graphically program and visualize this functionality.
3. 4.
As PWMMIN is changed, the automatic fan control slope changes.
PWM Maximum Duty Cycle Registers
Register 0x38, PWM1 Maximum Duty Cycle = 0xFF (100% default) Register 0x39, PWM2 Maximum Duty Cycle = 0xFF (100% default) Register 0x3A, PWM3 Maximum Duty Cycle = 0xFF (100% default)
PWM DUTY CYCLE
50% 33% 0% 30C TMIN
STEP 6--TRANGE FOR TEMPERATURE CHANNELS
TRANGE is the range of temperature over which automatic fan control occurs once the programmed TMIN temperature has been exceeded. TRANGE is the temperature range between PWMMIN and 100% PWM where the fan speed changes linearly. Otherwise stated, it is the line drawn between the TMIN/PWMMIN and the (TMIN + TRANGE)/PWM100% intersection points.
TRANGE 100%
PWM DUTY CYCLE
Figure 58. Adjusting PWMMIN Changes the Automatic Fan Control Slope.
As TRANGE is changed, the slope changes. As TRANGE gets smaller, the fans reach 100% speed with a smaller temperature change.
100%
PWM DUTY CYCLE
10% 0% 30C 40C 45C 54C
TMIN-HYST
PWMMIN 0% TMIN
05742-058
TMIN
TEMPERATURE
Figure 59. Increasing TRANGE Changes the AFC slope
Figure 57. TRANGE Parameter Affects Cooling Slope
Rev. 0 | Page 44 of 72
05742-060
05742-059
ADT7476A
100%
PWM DUTY CYCLE
MAX PWM
Decreasing the speed the PWM output changes by programming the smoothing on the appropriate temperature channels (Register 0x62 and Register 0x63) changes how fast the fan speed increases/decreases in the event of a temperature spike. The PWM duty cycle increases slowly until the PWM duty cycle reaches the appropriate duty cycle as defined by the AFC curve. Figure 61 shows PWM duty cycle vs. temperature for each TRANGE setting. The lower graph shows how each TRANGE setting affects fan speed vs. temperature. As can be seen from the graph, the effect on fan speed is nonlinear.
100 90 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
10% 0% TRANGE TMIN-HYST
05742-061
Figure 60. Changing PWM Max Does Not Change the AFC Slope
Selecting TRANGE
PWM DUTY CYCLE (%)
80 70 60 50 40 30 20 10 0 0
The TRANGE value can be selected for each temperature channel: Remote 1, local, and Remote 2 temperature. Bits [7:4] (TRANGE) of Register 0x5F to Register 0x61 define the TRANGE value for each temperature channel. Table 17. 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
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
(A)
100 90 80 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
05742-062
FAN SPEED (% OF MAX)
70 60 50 40 30 20 10 0 0
Register 0x5F configures Remote 1 TRANGE; Register 0x60 configures local TRANGE; Register 0x61 configures Remote 2 TRANGE.
Actual Changes in PWM Output (Advanced Acoustics Settings)
While the automatic fan control algorithm describes the general response of the PWM output, it is also necessary to note that the enhance acoustics registers (0x62 and 0x63) can be used to set/clamp the maximum rate of change of PWM output for a given temperature zone. This means that if TRANGE is programmed with an AFC slope that is quite steep, a relatively small change in temperature could cause a large change in PWM output and possibly an audible change in fan speed, which can be noticeable/ bothersome to end users.
(B)
Figure 61. TRANGE vs. Actual Fan Speed (Not PWM Drive) Profile
The graphs in Figure 61 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 62 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.
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ADT7476A
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
100 VRM TEMPERATURE 90 80
70 60 50 40 30 20 10 0 0
PWM DUTY CYCLE (%)
70 CPU TEMPERATURE 60 50 AMBIENT TEMPERATURE 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100
(A)
100 90 80
FAN SPEED (% OF MAX)
TEMPERATURE ABOVE TMIN
2C 2.5C 3.33C 4C 5C 6.67C 8C 10C 13.3C 16C 20C 26.6C 32C 40C 53.3C
05742-063
100 VRM TEMPERATURE 90 80
FAN SPEED (% MAX RPM)
70 60 50 40 30 20 10 0 0 20 40 60 80 TEMPERATURE ABOVE TMIN 100 120
70 60
CPU TEMPERATURE AMBIENT TEMPERATURE
50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100
05742-064
80C
(B)
TEMPERATURE ABOVE TMIN
Figure 62. TRANGE and % Fan Speed Slopes with PWMMIN = 20%
Figure 63. TRANGE and % Fan Speed Slopes for VRM, Ambient, and CPU Temperature Channels
Example: Determining TRANGE for Each Temperature Channel
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 = 53.33C for CPU temperature TRANGE = 40C for VRM temperature This example uses the mux configuration described in Step 2-- Configuring the Mux with the ADT7476A connected as shown in Figure 52. 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: The control range for 4-wire fans is much wider than that of 3-wire fans. In many cases, 4-wire fans can start with a PWM drive of as little as 20% or less. In extreme cases, some 3-wire fans cannot run unless a PWM drive of 60% or more is applied.
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 can operate 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. 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 users should ensure that it is not exceeded under normal system operating conditions.
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ADT7476A
Note: 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).
Hysteresis Registers
Register 0x6D, Remote 1, Local Temperature Hysteresis [7:4], Remote 1 temperature hysteresis (4C default). [3:0], Local temperature hysteresis (4C default). Register 0x6E, Remote 2 Temperature Hysteresis
THERM Limit Registers
Register 0x6A, Remote 1 THERM Limit = 0x64 (100C default) Register 0x6B, Local THERM Limit = 0x64 (100C default) Register 0x6C, Remote 2 THERM Limit = 0x64 (100C default) [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 to program hysteresis values to 0C, because this disables hysteresis. In effect, this causes the fans to cycle (during a THERM event) between normal speed and 100% speed, or, while operating close to TMIN, between normal speed and off, creating unsettling acoustic noise.
THERM Hysteresis
THERM hysteresis on a particular channel is configured via the hysteresis settings (Register 0x6D and Register 0x6E). For example, setting hysteresis on the Remote 1 channel also sets the hysteresis on Remote 1 THERM.
TRANGE 100%
PWM DUTYCYCLE
0%
TMIN
TTHERM
THERMAL CALIBRATION
100%
PWM MIN
PWM CONFIG PWM GENERATOR RAMP CONTROL (ACOUSTIC ENHANCEMENT) PWM1
TMIN REMOTE 2 = CPU TEMP
TRANGE
0% PWM MIN TACHOMETER 1 MEASUREMENT PWM CONFIG PWM GENERATOR RAMP CONTROL (ACOUSTIC ENHANCEMENT) PWM2 TACH1 CPU FAN SINK
THERMAL CALIBRATION
100%
MUX
0% PWM MIN
TMIN LOCAL = VRM TEMP
TRANGE
TACHOMETER 2 MEASUREMENT PWM CONFIG PWM GENERATOR RAMP CONTROL (ACOUSTIC ENHANCEMENT)
TACH2
THERMAL CALIBRATION
100%
FRONT CHASSIS PWM3
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0%
TACHOMETER 3 AND 4 MEASUREMENT
TACH3
REAR CHASSIS
Figure 64. How TTHERM Relates to Automatic Fan Control
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05742-065
ADT7476A
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 the temperature hovers around 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--TRANGE for Temperature Channels. Therefore, programming Register 0x6D and Register 0x6E sets the hysteresis for both fan on/off and the THERM function. In some applications, it is required that fans not turn off below TMIN but remain running at PWMMIN. Bits [7:5] of Enhance Acoustics Register 1 (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.
THERM Hysteresis
Any hysteresis programmed via Register 0x6D and Register 0x6E also applies hysteresis on the appropriate THERM channel.
TRANGE 100%
PWM DUTYCYCLE
0%
TMIN
TTHERM
THERMAL CALIBRATION
100%
PWM MIN
PWM CONFIG PWM GENERATOR RAMP CONTROL (ACOUSTIC ENHANCEMENT) PWM1
TMIN REMOTE 2 = CPU TEMP
TRANGE
0% PWM MIN
TACHOMETER 1 MEASUREMENT PWM CONFIG PWM GENERATOR RAMP CONTROL (ACOUSTIC ENHANCEMENT)
TACH1 CPU FAN SINK
THERMAL CALIBRATION
100%
MUX
0% PWM MIN
PWM2
TMIN LOCAL = VRM TEMP
TRANGE
TACHOMETER 2 MEASUREMENT PWM CONFIG PWM GENERATOR RAMP CONTROL (ACOUSTIC ENHANCEMENT)
TACH2
THERMAL CALIBRATION
100%
FRONT CHASSIS PWM3
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0%
TACHOMETER 3 AND 4 MEASUREMENT
TACH3
REAR CHASSIS
Figure 65. The THYST Value Applies to Fan On/Off Hysteresis and THERM Hysteresis
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05742-066
ADT7476A
Enhance Acoustics Register 1 (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 = 4.7 sec 101 = 3.1 sec 110 = 1.6 sec 111 = 0.8 sec [6:4] ACOU2 selects the ramp rate for PWM outputs associated with the Remote Temperature 2 input. 000 = 37.5 sec 001 = 18.8 sec 010 = 12.5 sec 011 = 7.5 sec 100 = 4.7 sec 101 = 3.1 sec 110 = 1.6 sec 111 = 0.8 sec When Bit 7 of Configuration Register 6 (0x10) = 1, the above ramp rates change to the values below. 000 = 52.2 sec 001 = 26.1 sec 010 = 17.4 sec 011 = 10.4 sec 100 = 6.5 sec 101 = 4.4 sec 110 = 2.2 sec 111 = 1.1 sec Setting the appropriate slow bit [2:0] of Configuration Register 6 (0x10) slows the ramp rate further by a factor of 4.
Configuration Register 6 (0x10)
[0] SLOW = 1, slows the ramp rate for PWM changes associated with the Remote 1 temperature channel by a factor of 4. [1] SLOW = 1, slows the ramp rate for PWM changes associated with the local temperature channel by a factor of 4. [2] SLOW = 1, slows the ramp rate for PWM changes associated with the Remote 2 temperature channel by a factor of 4. [7] ExtraSlow = 1, slows the ramp rate for all fans by a factor of 39.2%. The following sections list the ramp-up times when the SLOW bit is set for each temperature monitoring channel.
FAN PRESENCE DETECT
This feature is used to determine if a 4-wire fan is directly connected to a PWM output. This feature does not work for 3-wire fans. To detect whether a 4-wire fan is connected directly to a PWM output, the following must be performed in this order: 1. 2. 3. 4. 5. Drive the appropriate PWM outputs to 100% duty cycle. Set Bit 0 of Configuration Register 2 (0x73). Wait 5 ms. Program fans to run at a different speed if necessary. Read the state of Bits [3:1] of Configuration Register 2 (0x73). The state of these bits reflects whether a 4-wire fan is directly connected to the PWM output.
Enhance Acoustics Register 1 (0x62)
[2:0] ACOU selects the ramp rate for PWM outputs associated with the Remote Temperature 1 input. 000 = 37.5 sec 001 = 18.8 sec 010 = 12.5 sec 011 = 7.5 sec 100 = 4.7 sec 101 = 3.1 sec 110 = 1.6 sec 111 = 0.8 sec
Enhance Acoustics Register 2 (0x63)
[2:0] ACOU3 selects the ramp rate for PWM outputs associated with the local temperature channel. 000 = 37.5 sec 001 = 18.8 sec 010 = 12.5 sec 011 = 7.5 sec
As the detection time only takes 5 ms, programming the PWM outputs to 100% and then back to its normal speed is not noticeable in most cases.
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ADT7476A
How Fan Presence Detect Works
4-wire fans typically have an internal pull up to 4.75 V 10%, which typically sources 5 mA. While the detection cycle is on, an internal current sink is turned on, which sinks current from the fan's internal pull-up. By driving some of the current from the fan's internal pull-up (~100 A) the logic buffer switches to a defined logic state. If this state is high, a fan is present; if the state is low, no fan is present. Note: The PWM input voltage should be clamped to 3.3 V. This ensures the PWM output is not pulled to a voltage higher than the maximum allowable voltage on that pin (5.5 V).
XNOR TREE TEST MODE
The ADT7476A 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 (0x6F). Figure 66 shows the signals that are exercised in the XNOR tree test mode.
VID0 VID1
FAN SYNC
When two ADT7476As are used in a system, it is possible to synchronize them so that one PWM channel from each device can be effectively OR'ed together to create a PWM output that reflects the maximum speed of the two OR'ed PWMs. This OR'ed PWM can in turn be used to drive a chassis fan. See the Analog Devices website (www.analog.com) for information on the Fan SYNC function.
VID2
VID3
VID4
TACH1
STANDBY MODE
The ADT7476A has been specifically designed to respond to the STBY supply. In computers that support S3 and S5 states, the core voltage of the processor is lowered in these states. When monitoring THERM, the THERM timer should be disabled during these states. When the VCCP voltage drops below the VCCP low limit, the following occurs: 1. 2. 3. Status Bit 1 (VCCP) in Interrupt 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.
TACH2 TACH3
TACH4
PWM2
05742-067
PWM3
PWM1/XTO
Figure 66. XNOR Tree Test
POWER-ON DEFAULT
When the ADT7476A is powered up, monitoring is off by default and the PWM outputs go to 100%. All necessary registers then need to be configured via the SMBus for the appropriate functions to operate.
Once the core voltage, VCCP, goes above the VCCP low limit, everything is re-enabled and the system resumes normal operation.
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ADT7476A REGISTER TABLES
Table 18. ADT7476A Registers
Address 0x10 0x11 0x20 0x21 0x22 0x23 0x24 0x25 0x26 0x27 0x28 0x29 0x2A 0x2B 0x2C 0x2D 0x2E 0x2F 0x30 0x31 0x32 0x38 0x39 0x3A 0x3D 0x3E 0x3F 0x40 0x41 0x42 0x43 0x44 0x45 0x46 0x47 0x48 R/W R/W 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 R R R/W R R R/W R/W R/W R/W R/W R/W Description Configuration Register 6 Configuration Register 7 2.5 V Measurement VCCP Measurement VCC Measurement 5V 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 PWM1 Max Duty Cycle PWM2 Max Duty Cycle PWM3 Max Duty Cycle Device ID Register Company ID Number Revision ID Configuration Register 1 Interrupt Status Register 1 Interrupt Status Register 2 VID/GPIO 2.5 V Low Limit 2.5 V High Limit VCCP Low Limit VCCP High Limit VCC Low Limit Bit 7 ExtraSlow RES 9 9 9 9 9 9 9 9 7 15 7 15 7 15 7 15 7 7 7 7 7 7 7 7 7 RES OOL D2 VIDSEL 7 7 7 7 7 Bit 6 VCCP Low RES 8 8 8 8 8 8 8 8 6 14 6 14 6 14 6 14 6 6 6 6 6 6 6 6 6 TODIS R2T D1 THLD 6 6 6 6 6 Bit 5 MasterEn RES 7 7 7 7 7 7 7 7 5 13 5 13 5 13 5 13 5 5 5 5 5 5 5 5 5 FSPDIS LT F4P VID 5 5 5 5 5 5 Bit 4 SlaveEn RES 6 6 6 6 6 6 6 6 4 12 4 12 4 12 4 12 4 4 4 4 4 4 4 4 4 Vx1 R1T FAN3 VID4/GPIO4 4 4 4 4 4 Bit 3 THERM in Manual RES 5 5 5 5 5 5 5 5 3 11 3 11 3 11 3 11 3 3 3 3 3 3 3 3 3 FSPD 5V FAN2 VID3/GPIO3 3 3 3 3 3 Bit 2 SlowFan Remote 1 RES 4 4 4 4 4 4 4 4 2 10 2 10 2 10 2 10 2 2 2 2 2 2 2 2 2 RDY VCC FAN1 VID2/GPIO2 2 2 2 2 2 Bit 1 SlowFan Local RES 3 3 3 3 3 3 3 3 1 9 1 9 1 9 1 9 1 1 1 1 1 1 1 1 1 LOCK VCCP OVT VID1/GPIO1 1 1 1 1 1 Bit 0 SlowFan Remote 1 DisTHERMHys 2 2 2 2 2 2 2 2 0 8 0 8 0 8 0 8 0 0 0 0 0 0 0 0 0 STRT 2.5 V/THERM 12 V/VC VID 0/GPIO 0 0 0 0 0 0 Default 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x80 0x80 0x80 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0x76 0x41 0x6B 0x04 0x00 0x00 0x1F 0x00 0xFF 0x00 0xFF 0x00 Yes Yes Yes Yes Lockable? Yes Yes
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ADT7476A
Address 0x49 0x4A 0x4B 0x4C 0x4D 0x4E 0x4F 0x50 0x51 0x52 0x53 0x54 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 VCC High Limit 5 V Low Limit 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 PWM2 Configuration PWM3 Configuration Remote 1 TRANGE/PWM1 Frequency Local TRANGE/PWM2 Frequency Remote 2 TRANGE/PWM3 Frequency Enhance Acoustics Register 1 Enhance Acoustics Register 2 PWM1 Min Duty Cycle PWM2 Min Duty Cycle PWM3 Min Duty Cycle Remote 1 Temp TMIN Bit 7 7 7 7 7 7 7 7 7 7 7 7 7 Bit 6 6 6 6 6 6 6 6 6 6 6 6 6 Bit 5 5 5 5 5 5 5 5 5 5 5 5 5 Bit 4 4 4 4 4 4 4 4 4 4 4 4 4 Bit 3 3 3 3 3 3 3 3 3 3 3 3 3 Bit 2 2 2 2 2 2 2 2 2 2 2 2 2 Bit 1 1 1 1 1 1 1 1 1 1 1 1 1 Bit 0 0 0 0 0 0 0 0 0 0 0 0 0 Default 0xFF 0x00 0xFF 0x00 0xFF 0x81 0x7F 0x81 0x7F 0x81 0x7F 0xFF Lockable?
0x55
R/W
15
14
13
12
11
10
9
8
0xFF
0x56
R/W
7
6
5
4
3
2
1
0
0xFF
0x57
R/W
15
14
13
12
11
10
9
8
0xFF
0x58
R/W
7
6
5
4
3
2
1
0
0xFF
0x59
R/W
15
14
13
12
11
10
9
8
0xFF
0x5A
R/W
7
6
5
4
3
2
1
0
0xFF
0x5B
R/W
15
14
13
12
11
10
9
8
0xFF
0x5C 0x5D 0x5E 0x5F
R/W R/W R/W R/W
BHVR BHVR BHVR RANGE
BHVR BHVR BHVR RANGE
BHVR BHVR BHVR RANGE
INV INV INV RANGE
RES RES RES HF/LF
SPIN SPIN SPIN FREQ
SPIN SPIN SPIN FREQ
SPIN SPIN SPIN FREQ
0x62 0x62 0x62 0XC4
Yes Yes Yes Yes
0x60
R/W
RANGE
RANGE
RANGE
RANGE
HF/LF
FREQ
FREQ
FREQ
0XC4
Yes
0x61
R/W
RANGE
RANGE
RANGE
RANGE
HF/LF
FREQ
FREQ
FREQ
0XC4
Yes
0x62
R/W
MIN3
MIN2
MIN1
SYNC
EN1
ACOU
ACOU
ACOU
0X00
Yes
0x63
R/W
EN2
ACOU2
ACOU2
ACOU2
EN3
ACOU3
ACOU3
ACOU3
0X00
Yes
0x64 0x65 0x66 0x67
R/W R/W R/W R/W
7 7 7 7
6 6 6 6
5 5 5 5
4 4 4 4
3 3 3 3
2 2 2 2
1 1 1 1
0 0 0 0
0X80 0X80 0X80 0X5A
Yes Yes Yes Yes
Rev. 0 | Page 52 of 72
ADT7476A
Address 0x68 0x69 0x6A 0x6B 0x6C 0x6D R/W R/W R/W R/W R/W R/W R/W Description Local Temp TMIN Remote 2 Temp TMIN Remote 1 THERM Limit Local THERM Limit Remote 2 THERM 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 Register 1 Interrupt Mask Register 2 Extended Resolution Register 1 Extended Resolution Register 2 Configuration Register 3 THERM Timer Status THERM Timer Limit TACH Pulses per Revolution Configuration Register 5 Bit 7 7 7 7 7 7 HYSR1 Bit 6 6 6 6 6 6 HYSR1 Bit 5 5 5 5 5 5 HYSR1 Bit 4 4 4 4 4 4 HYSR1 Bit 3 3 3 3 3 3 HYSL Bit 2 2 2 2 2 2 HYSL Bit 1 1 1 1 1 1 HYSL Bit 0 0 0 0 0 0 HYSL Default 0X5A 0X5A 0X64 0X64 0X64 0X44 Lockable? Yes Yes Yes Yes Yes Yes
0x6E
R/W
HYSR2
HYSR2
HYSR2
HYRS
RES
RES
RES
RES
0X40
Yes
0x6F 0x70
R/W R/W
RES 7
RES 6
RES 5
RES 4
RES 3
RES 2
RES 1
XEN 0
0X00 0X00
Yes Yes
0x71
R/W
7
6
5
4
3
2
1
0
0X00
Yes
0x72
R/W
7
6
5
4
3
2
1
0
0X00
Yes
0x73 0x74 0x75 0x76
R/W R/W R/W R/W
RES OOL D2 5V
CONV R2T D1 5V
ATTN LT F4P VCC
AVG R1T FAN3 VCC
Fan3Detect 5V FAN2 VCCP
Fan2Detect VCC FAN1 VCCP
Fan1Detect VCCP OVT 2.5 V
FanPresenceDT 2.5 V/THERM 12 V/VC 2.5 V
0X00 0X00 0X00 0X00
Yes
0x77
R/W
TDM2
TDM2
LTMP
LTMP
TDM1
TDM1
12 V
12 V
0X00
0x78 0x79 0x7A 0x7B 0x7C
R/W R R/W R/W R/W
DC4 TMR LIMT FAN4 R2 THERM (O/P Only)
DC3 TMR LIMT FAN4 Local THERM (O/P Only) BpAtt 5V
DC2 TMR LIMT FAN3 R1 THERM (O/P Only) BpAtt VCCP
DC1 TMR LIMT FAN3 VID/ GPIO
FAST TMR LIMT FAN2 GPIO6P
BOOST TMR LIMT FAN2 GPIO6D
THERM /2.5V TMR LIMT FAN1 TempOffset
ALERT ASRT/TMRO LIMT FAN1 2sC
0x00 0x00 0x00 0x55 0x01
Yes
Yes
0x7D 0x7E 0x7F
R/W R R
Configuration Register 4 Test 1 Test 2
BpAtt 12 V
BpAtt 2.5 V
THERM Disable Do not write to these registers Do not write to these registers
MaxSpeed on THERM
PIN14FUNC
PIN14FUNC
0x00 0x00 0x00
Yes Yes Yes
Rev. 0 | Page 53 of 72
ADT7476A
Table 19. Register 0x10--Configuration Register 6 (Power-On Default = 0x00) 1, 2
Bit [0] [1] [2] [3] [4] [5] [6] Mnemonic SlowFan Remote 1 SlowFan Local SlowFan Remote 2 THERM in Manual SlaveEn MasterEn VCCPLow R/W Read/Write Read/Write Read/Write Read/Write Read/Write Read/Write Read/Write Description When this bit is set, Fan 1 smoothing times are multiplied x4 for Remote 1 temperature channel (as defined in Register 0x62). When this bit is set, Fan 2 smoothing times are multiplied x4 for local temperature channel (as defined in Register 0x63). When this bit is set, Fan 3 smoothing times are multiplied x4 for Remote 2 temperature channel (as defined in Register 0x63). When this bit is set, THERM is enabled in manual mode1. Setting this bit configures the ADT7476A as a slave for use in fan sync mode. Setting this bit configures the ADT7476A as a master for use in fan sync mode. VCCPLow = 1. When the power is supplied from 3.3 V STANDBY and the core voltage (VCCP) drops below its VCCP low limit value (Register 0x46), the following occurs: * Status Bit 1 in Interrupt Status Register 1 is set. * SMBALERT is generated, if enabled. * PROCHOT monitoring is disabled.
* Everything is re-enabled once VCCP increases above the VCCP low limit. When VCCP increases above the low limit: * PROCHOT monitoring is enabled.
[7]
1 2
ExtraSlow
Read/Write
* Fans return to their programmed state after a spin-up cycle. When this bit is set, all fan smoothing times are increased by a further 39.2%
A THERM event always overrides any fan setting (even when fans are disabled). 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 20. Register 0x11--Configuration Register 7 (Power-On Default = 0x00) 1
Bit [0] [7:1]
1
Mnemonic
DisTHERMHys
Reserved
R/W Read/Write N/A
Description Setting this bit to 1 disables THERM hysteresis. Reserved. Do not write to these bits.
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 21. Voltage Reading Registers (Power-On Default = 0x00)1
Register Address 0x20 0x21 0x22 0x23 0x24
1
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).
If the extended resolution bits of these readings are also being read, the extended resolution registers (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. If VCCPLow (Bit 7 of 0x40) is set, VCCP can control the sleep state of the ADT7476A. 3 VCC (Pin 4) is the supply voltage for the ADT7476A.
2
Rev. 0 | Page 54 of 72
ADT7476A
Table 22. Temperature Reading Registers (Power-On Default = 0x80)1, 2, 3
Register Address 0x25 0x26 0x27
1
R/W Read-only Read-only Read-only
Description Remote 1 temperature reading3, 4 (8 MSBs of reading). Local temperature reading (8 MSBs of reading). Remote 2 temperature reading3, 4 (8 MSBs of reading).
If the extended resolution bits of these readings are also being read, the extended resolution registers (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 23. 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 TACH Pulses per Revolution Register (0x7B). This allows the fan speed to be accurately measured. Because a valid fan tachometer reading requires that two bytes be 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 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), or not populated. (The ADT7476A 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.
Table 24. PWM Current Duty Cycle Registers (Power-On Default = 0xFF)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 ADT7476A 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 manual mode, the PWM duty cycle outputs can be set to any duty cycle value by writing to these registers.
Table 25. PWM Maximum 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 55 of 72
ADT7476A
Table 26. Register 0x40--Configuration Register 1 (Power-On Default = 0x04)
Bit [0] Name STRT1,2 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 is 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 does not become locked once Bit 1 (LOCK bit) has been set. 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 ADT7476A 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 ADT7476A to indicate that the device is fully powered-up and ready to begin system monitoring. When set to 1, this bit runs all fans at max speed as programmed in the max PWM current duty cycle registers (0x30 to 0x32). Power-on default = 0. This bit is not locked at any time. BIOS should set this bit to a 1 when the ADT7476A is configured to measure current from an ADOPT(R) 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. In this state, if at any point during an SMBus transaction involving the ADT7476A activity ceases for more than 35 ms, the ADT7476A assumes the bus is locked and releases the bus. This allows the ADT7476A to be used with SMBus controllers that cannot handle SMBus timeouts. (Lockable.) Reserved. Do not write to this bit.
[1]
LOCK
Write once
[2] [3] [4]
RDY FSPD Vx1
Read-only Read/Write Read/Write
[5] [6]
FSPDIS TODIS
Read/Write Read/Write
[7]
1
Reserved
N/A
Bit 0 (STRT) of Configuration Register 1 (0x40) remains writable after lock bit is set. 2 When monitoring (STRT) is disabled, PWM outputs always go to 100% for thermal protection.
Table 27. Register 0x41--Interrupt Status Register 1 (Power-On Default = 0x00)
Bit [0] Name 2.5 V/ THERM VCCP VCC 5V R1T LT R2T OOL R/W 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. If Pin 22 is configured as THERM, this bit is asserted when the timer limit has been exceeded. 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 1 indicates that 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. 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 Interrupt Status Register 2. This bit is a logical OR of all status bits in Interrupt Status Register 2. Software can test this bit in isolation to determine whether any of the voltage, temperature, or fan speed readings represented by Interrupt Status Register 2 are out-of-limit, which eliminates the need to read Interrupt Status Register 2 during every interrupt or polling cycle.
[1] [2] [3] [4] [5] [6] [7]
Read-only Read-only Read-only Read-only Read-only Read-only Read-only
Rev. 0 | Page 56 of 72
ADT7476A
Table 28. Register 0x42--Interrupt Status Register 2 (Power-On Default = 0x00)
Bit [0] Name 12 V/VC R/W Read-only Description A 1 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 PWM1 output is off. FAN2 = 1 indicates that Fan 2 has dropped below minimum speed or has stalled. This bit is not set when the PWM2 output is off. FAN3 = 1 indicates that Fan 3 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 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 the GPIO6 output, writing to this bit determines the logic output of GPIO6. When GPIO6 is programmed as an input, this bit reflects the value read by GPIO6. 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 timer limit register (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 29. Register 0x43--VID/GPIO Register (Power-On Default = 0x1F )
Bit [4:0] Name VID[4:0]/ GPIO[4:0] R/W 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. When Bit 4 of Configuration Register 5 (0x7C) = 1, these bits become general-purpose outputs. The state of these bits then reflects the state of the appropriate GPIO pin. Reads VID5 from the CPU when Bit 7 = 1. If Bit 7 = 0, 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).
[5] [6]
VID5 THLD
Read/Write Read/Write
[7]
VIDSEL
Read/Write
Table 30. 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 low limit. 2.5 V high limit. 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).
Rev. 0 | Page 57 of 72
ADT7476A
Table 31. Temperature Limit Registers1
Register Address 0x4E 0x4F 0x50 0x51 0x52 0x53
1
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
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 32. Fan TACH Limit Registers1
Register Address 0x54 0x55 0x56 0x57 0x58 0x59 0x5A 0x5B
1
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
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 33. Register 0x55--TACH1 Minimum High Byte (Power-On Default = 0xFF)
Bits [4:0] [7:5] Name Reserved SCADC R/W Read-only Read/Write Description When Bit 6 of Configuration 2 Register (0x73) is set (single-channel ADC mode), these bits are reserved. Otherwise, these bits represent Bits [4:0] of the TACH1 minimum high byte. When Bit 6 of Configuration 2 Register (0x73) is set (single-channel ADC mode), these bits are used to select the only channel from which the ADC will take measurements. Otherwise, these bits represent Bits [7:5] of the TACH1 minimum high byte.
Rev. 0 | Page 58 of 72
ADT7476A
Table 34. 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. 0x62 PWM2 configuration. 0x62 PWM3 configuration. 0x62 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, the TACH measurement reads 0xFFFF and Interrupt Status Register 2 reflects the fan fault. If the TACH minimum high and low bytes contain 0xFFFF or 0x0000, the Interrupt 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 sec 110 = 2 sec 111 = 4 sec Reserved. Do not write to this bit. 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 (default). 100 = PWMx disabled. 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 current duty cycle registers (0x30 to 0x32) become writable.
Name SPIN
[3] [4]
RES INV
N/A 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.
Rev. 0 | Page 59 of 72
ADT7476A
Table 35. 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 TRANGE/PWM2 frequency. 0xC4 Remote 2 TRANGE/PWM3 frequency. 0xC4 Description These bits control the PWMx frequency (only apply when PWM channel is in low frequency mode). 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 HF/LF = 1, High frequency PWM mode is enabled for PWMx. HF/LF = 0, Low frequency PWM mode is enabled for PWMx. These bits determine the PWM duty cycle vs. the temperature range 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] [7:4]
HF/LF RANGE
Read/Write 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.
Rev. 0 | Page 60 of 72
ADT7476A
Table 36. Register 0x62--Enhance Acoustics Register 1 (Power-On Default = 0x00)
Bit [2:0] Name ACOU2 R/W1 Read/Write Description Assuming that PWMx is associated with the Remote 1 temperature channel, these bits define the maximum rate of change of the PWMx output for Remote 1 temperature-related changes. Instead of the fan speed jumping instantaneously to its newly determined speed, it ramps gracefully at the rate determined by these bits. This feature ultimately enhances the acoustics of the fan. When Bit 7 of Configuration Register 6 (0x10) is 0 Time Slot Increase Time for 0% to 100% 000 = 1 37.5 sec 001 = 2 18.8 sec 010 = 3 12.5 sec 011 = 4 7.5 sec 100 = 8 4.7 sec 101 = 12 3.1 sec 110 = 24 1.6 sec 111 = 48 0.8 sec When Bit 7 of Configuration Register 6 (0x10) is 1 Time Slot Increase Time for 0% to 100% 000 = 1 52.2 sec 001 = 2 26.1 sec 010 = 3 17.4 sec 011 = 4 10.4 sec 100 = 8 6.5 sec 101 = 12 4.4 sec 110 = 24 2.2 sec 111 = 48 1.1 sec When this bit is 1, smoothing is enabled on Remote 1 temperature channel. 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 ADT7476A 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 ADT7476A 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 ADT7476A 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 2
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. Setting the relevant bit of Configuration Register 6, (0x10, [2:0]), further decreases these ramp rates by a factor of 4.
Rev. 0 | Page 61 of 72
ADT7476A
Table 37. Register 0x63--Enhance Acoustics Register 2 (Power-On Default = 0x00)
Bit [2:0] Name ACOU3 R/W1 Read/Write Description Assuming that PWMx is associated with the local temperature channel, these bits define the maximum rate of change of the PWMx output for local temperature-related changes. Instead of the fan speed jumping instantaneously to its newly determined speed, it ramps gracefully at the rate determined by these bits. This feature ultimately enhances the acoustics of the fan. When Bit 7 of Configuration Register 6 (0x10) is 0 Time Slot Increase Time for 0% to 100% 000 = 1 37.5 sec 001 = 2 18.8 sec 010 = 3 12.5 sec 011 = 4 7.5 sec 100 = 8 4.7 sec 101 = 12 3.1 sec 110 = 24 1.6 sec 111 = 48 0.8 sec When Bit 7 of Configuration Register 6 (0x10) is 1 Time Slot Increase Time for 0% to 100% 000 = 1 52.2 sec 001 = 2 26.1 sec 010 = 3 17.4 sec 011 = 4 10.4 sec 100 = 8 6.5 sec 101 = 12 4.4 sec 110 = 24 2.2 sec 111 = 48 1.1 sec When this bit is 1, smoothing is enabled on the local temperature channel. Assuming that PWMx is associated with the Remote 2 temperature channel, these bits define the maximum rate of change of the PWMx output for Remote 2 temperature related changes. Instead of the fan speed jumping instantaneously to its newly determined speed, it ramps gracefully at the rate determined by these bits. This feature ultimately enhances the acoustics of the fan. When Bit 7 of Configuration Register 6 (0x10) is 0 Time Slot Increase Time for 0% to 100% 000 = 1 37.5 sec 001 = 2 18.8 sec 010 = 3 12.5 sec 011 = 4 7.5 sec 100 = 8 4.7 sec 101 = 12 3.1 sec 110 = 24 1.6 sec 111 = 48 0.8 sec When Bit 7 of Configuration Register 6 (0x10) is 1 Time Slot Increase Time for 0% to 100% 000 = 1 52.2 sec 001 = 2 26.1 sec 010 = 3 17.4 sec 011 = 4 10.4 sec 100 = 8 6.5 sec 101 = 12 4.4 sec 110 = 24 2.2 sec 111 = 48 1.1 sec When this bit is 1, smoothing is enabled on the Remote 2 temperature channel.
[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.
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ADT7476A
Table 38. 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 ADT7476A is in automatic fan control mode.
Table 39. TMIN Registers1
Register Address 0x67 0x68 0x69
1
R/W2 Read/Write Read/Write Read/Write
Description Remote 1 temperature TMIN. Local temperature TMIN. Remote 2 temperature TMIN.
Power-On Default 0x5A (90C) 0x5A (90C) 0x5A (90C)
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.
Table 40. 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, 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 41. Temperature/TMIN Hysteresis Registers1
Register Address 0x6D [3:0] [7:4] 0x6E [7:4]
1
R/W2 Read/Write HYSL HYSR1 Read/Write HYSR2
Description Remote 1 and local temperature hysteresis. Local temperature hysteresis. 0C to 15C of hysteresis can be applied to the local temperature AFC control loops. Remote 1 temperature hysteresis. 0C to 15C of hysteresis can be applied to the Remote 1 temperature AFC control loops. Remote 2 temperature hysteresis. Local temperature hysteresis. 0C to 15C of hysteresis can be applied to the local temperature AFC control loops.
Power-On Default 0x44
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.
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ADT7476A
Table 42. XNOR Tree Test Enable
Register Address 0x6F [0] [7:1]
1
R/W1 Read/Write XEN Reserved
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
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 43. Remote 1 Temperature Offset1
Register Address 0x70 [7:0] R/W1 Read/Write Read/Write Description Remote 1 temperature offset. Allows a temperature offset to be automatically applied to the Remote Temperature 1 channel measurement. Bit 1 of Configuration Register 5 (0x7C) determines the range and resolution of this register. 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. Local Temperature Offset1
Register Address 0x71 [7:0] R/W1 Read/Write Read/Write Description Local temperature offset. Allows a temperature offset to be automatically applied to the local temperature measurement. Bit 1 of Configuration Register 5 (0x7C) determines the range and resolution of this register. 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. Remote 2 Temperature Offset1
Register Address 0x72 [7:0] R/W1 Read/Write Read/Write Description Remote 2 temperature offset. Allows a temperature offset to be automatically applied to the Remote Temperature 2 channel measurement. Bit 1 of Configuration Register 5 (0x7C) determines the range and resolution of this register. 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.
Rev. 0 | Page 64 of 72
ADT7476A
Table 46. Register 0x73--Configuration Register 2 (Power-On Default = 0x00)1
Bit 0 1 2 3 4 5 Name FanPresenceDT Fan1Detect Fan2Detect Fan3Detect AVG ATTN R/W1 Read/Write Read Read Read Read/Write Read/Write Description When FanPresenceDT = 1, the state of Bits [3:1] of 0x73 reflects the presence of a 4-wire fan on the appropriate TACH channel. Fan1Detect = 1 indicates that a 4-wire fan is connected to the TACH 1 input. Fan2Detect = 1 indicates that a 4-wire fan is connected to the TACH 2 input. Fan3Detect = 1 indicates that a 4-wire fan is connected to the TACH 3 input. AVG = 1 indicates that averaging on the temperature and voltage measurements is turned off. This allows measurements on each channel to be made much faster. (x16). ATTN = 1 indicates that the ADT7476A removes the attenuators from the +2.5VIN, VCCP, +5VIN, and +12VIN inputs. These inputs can be used for other functions such as connecting up external sensors. It is also possible to remove attenuators from individual channels using Bits [7:4] of Configuration Register 4 (0x7D). CONV = 1 indicates that the ADT7476A is put into a single-channel ADC conversion mode. In this mode, the ADT7476A 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] Register 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 This bit is reserved and should not be changed.
6
CONV
Read/Write
7
1
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.
Table 47. Register 0x74--Interrupt Mask Register 1 (Power-On Default [7:0] = 0x00)
Bit 0 1 2 3 4 5 6 7 Name 2.5V/THERM VCCP VCC 5V R1T LT R2T OOL R/W Read/Write Read/Write Read/Write Read/Write Read/Write Read/Write Read/Write Read/Write Description 2.5V/ THERM = 1, masks SMBALERT for out-of-limit conditions on the 2.5 V/ THERM timer 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. R1T = 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 = 0 when one or more alerts are generated in Interrupt Status Register 2, assuming all the mask bits in the Interrupt Mask Register 2 (0x75) =1, SMBALERT is still asserted. OOL = 1 when one or more alerts are generated in Interrupt Status Register 2, assuming all the mask bits in the Interrupt Mask Register 2 (0x75) =1, SMBALERT is not asserted.
Rev. 0 | Page 65 of 72
ADT7476A
Table 48. Register 0x75--Interrupt Mask Register 2 (Power-On Default [7:0] = 0x00)
Bit 0 Name 12 V/VC R/W Read/Write Description When Pin 21 is configured as a 12 V input, 12 V/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 TACH4, 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.
1 2 3 4 5
OVT FAN1 FAN2 FAN3 F4P
Read Only Read/Write Read/Write Read/Write Read/Write
6 7
D1 D2
Read/Write Read/Write
Table 49. Register 0x76--Extended Resolution Register 11 (Power-On Default [7:0] = 0x00)
Bit [1:0] [3:2] [5:4] [7:6]
1
Name 2.5 V 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 50. Register 0x77--Extended Resolution Register 21 (Power-On Default [7:0] = 0x00)
Bit [1:0] [3:2] [5:4] [7:6]
1
Name 12 V 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.
Rev. 0 | Page 66 of 72
ADT7476A
Table 51. 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 = 1 enables THERM functionality on Pin 22 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, then 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. THERM = 0 enables 2.5 V measurement on Pin 22 and disables THERM. If bits [5:7] of Configuration Register 5 are set, THERM is bidirectional. If they are 0, THERM is a timer input only. Pin14FUNC 00 01 10 11 00 01 10 11 [2] [3] [4] [5] [6] [7]
1
[1]
THERM/ 2.5 V
Read/Write
THERM/2.5 V 0 0 0 0 1 1 1 1
Pin 22 +2.5VIN +2.5VIN +2.5VIN +2.5VIN THERM +2.5VIN THERM THERM
Pin 14 TACH4 THERM SMBALERT GPIO6 TACH4 THERM SMBALERT GPIO6
BOOST FAST DC1 DC2 DC3 DC4
Read/Write Read/Write Read/Write Read/Write Read/Write Read/Write
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.
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 52. Register 0x79--THERM Timer Status Register (Power-On Default = 0x00)
Bit [7:1] [0] Name TMR ASRT/TMRO 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 sec to be reported back with a resolution of 22.76 ms.
Table 53. 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 sec to be programmed. If the THERM assertion time exceeds this limit, Bit 5 (F4P) of Interrupt Status Register 2 (0x42) is set. If the limit value is 0x00, an interrupt is generated immediately on the assertion of the THERM input.
Rev. 0 | Page 67 of 72
ADT7476A
Table 54. 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
Rev. 0 | Page 68 of 72
ADT7476A
Table 55. Register 0x7C--Configuration Register 5 (Power-On Default = 0x01)
Bit [0] Name 2sC R/W1 Read/Write Description 2sC = 1 sets the temperature range to the twos complement temperature range. 2sC = 0 changes the temperature range to the Offset 64 temperature range. When this bit is changed, the ADT7476A interprets all relevant temperature register values as defined by this bit. TempOffset = 0 sets offset range to -63C to +64C with 0.5C resolution. TempOffset = 1 sets offset range to -63C to +127C with 1C resolution. These settings apply to Remote 1, Local, and Remote2 temperature offset registers (0x70, 0x71, and 0x72). GPIO6 direction. When GPIO6 function is enabled, this determines whether GPIO6 is an input (0) or an output (1). GPIO6 polarity. When the GPIO6 function is enabled and is programmed as an output, this bit determines whether the GPIO6 is active low (0) or high (1). VID/GPIO = 0 enables VID functionality on Pin 5, Pin 6, Pin 7, Pin 8, and Pin 19. VID/GPIO = 1 enables GPIO functionality on Pin 5, Pin 6, Pin 7, Pin 8, and Pin 19. R1 THERM = 1 enables THERM temperature limit functionality for Remote 1 temperature channel; that is, THERM is bidirectional. R1 THERM = 0 indicates THERM is a timer input only. THERM can also be disabled on any channel by: Writing -64C to the appropriate THERM temperature limit in Offset 64 mode. Writing -128C to the appropriate THERM temperature limit in twos complement mode. Local THERM = 1 enables THERM temperature limit functionality for local temperature channel; that is, THERM is bidirectional. Local THERM = 0 indicates THERM is a timer input only. THERM can also be disabled on any channel by: Writing -64C to the appropriate THERM temperature limit in Offset 64 mode. Writing -128C to the appropriate THERM temperature limit in twos complement mode. R2 THERM = 1 enables THERM temperature limit functionality for Remote 2 temperature channel; that is, THERM is bidirectional. R2 THERM = 0 indicates THERM is a timer input only. THERM can also be disabled on any channel by: Writing -64C to the appropriate THERM temperature limit in Offset 64 mode. Writing -128C to the appropriate THERM temperature limit in twos complement mode.
[1]
TempOffset
Read/Write
[2] [3] [4] [5]
GPIO6D GPIO6P VID/GPIO R1 THERM
Read/Write Read/Write Read/Write Read/Write
[6]
Local THERM
Read/Write
[7]
R2 THERM
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 69 of 72
ADT7476A
Table 56. 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 = THERM 10 = SMBALERT 11 = GPIO THERM Disable = 0 enables THERM overtemperature output assuming THERM is correctly configured (Register 0x78, Register 0x7C, and Register 0x7D). THERM Disable = 1 disables THERM overtemperature output on all channels. THERM can also be disabled on any channel by: Writing -64C to the appropriate THERM temperature limit in Offset 64 mode. Writing -128C to the appropriate THERM temperature limit in twos complement mode. MaxSpeed on THERM = 0 indicates that fans go to full speed when THERM temperature limit is exceeded. MaxSpeed on THERM = 1 indicates that fans go to max speed (0x38, 0x39, 0x3A) when THERM temperature limit is exceeded. Bypass 2.5 V attenuator. When set, the measurement scale for this channel changes from 0 V (0x00) to 2.25 V (0xFF). Bypass VCCP attenuator. When set, the measurement scale for this channel changes from 0 V (0x00) to 2.25 V (0xFF). Bypass 5 V attenuator. When set, the measurement scale for this channel changes from 0 V (0x00) to 2.25 V (0xFF). Bypass 12 V attenuator. When set, the measurement scale for this channel changes from 0 V (0x00) to 2.25 V (0xFF).
[2]
THERM Disable
Read/Write
[3]
MaxSpeed on THERM BpAtt 2.5 V BpAtt VCCP BpAtt 5 V BpAtt 12 V
Read/Write
[4] [5] [6] [7]
1
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 57. 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 58. 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 70 of 72
ADT7476A OUTLINE DIMENSIONS
0.345 0.341 0.337
24
13
0.158 0.154 0.150
1 12
0.244 0.236 0.228
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 67. 24-Lead Shrink Small Outline Package [QSOP] (RQ-24) Dimensions shown in inches
ORDERING GUIDE
Model ADT7476AARQZ 1 ADT7476AARQZ-REEL1 ADT7476AARQZ-REEL71
1
Temperature Range -40C to +125C -40C to +125C -40C to +125C
Package Description 24-Lead Shrink Small Outline Package [QSOP] 24-Lead Shrink Small Outline Package [QSOP] 24-Lead Shrink Small Outline Package [QSOP]
Package Option RQ-24 RQ-24 RQ-24
Z = Pb-free part.
Rev. 0 | Page 71 of 72
ADT7476A NOTES
(c)2006 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D05742-0-1/06(0)
Rev. 0 | Page 72 of 72

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