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dBCool(R) Remote Thermal Monitor and Fan Controller ADT7473
FEATURES
Controls and monitors up to 4 fans High and low frequency fan drive signal 1 on-chip and 2 remote temperature sensors Series resistance cancellation on the remote channel Extended temperature measurement range, up to 191C Dynamic TMIN control mode optimizes system acoustics intelligently Automatic fan speed control mode controls system cooling based on measured temperature Enhanced acoustic mode dramatically reduces user perception of changing fan speeds Thermal protection feature via THERM output Monitors performance impact of Intel(R) Pentium(R)4 processor Thermal control circuit via THERM input 3-wire and 4-wire fan speed measurement Limit comparison of all monitored values Meets SMBus 2.0 electrical specifications (fully SMBus 1.1 compliant) Fully ROHS compliant
GENERAL DESCRIPTION
The ADT7473 dBCool controller is a thermal monitor and multiple PWM fan controller for noise sensitive or power sensitive applications requiring active system cooling. The ADT7473 can drive a fan using either a low or high frequency drive signal, monitor the temperature of up to two remote sensor diodes plus its own internal temperature, and measure and control the speed of up to four fans so they operate at the lowest possible speed for minimum acoustic noise. The automatic fan speed control loop optimizes fan speed for a given temperature. A unique dynamic TMIN control mode enables the system thermals/acoustics to be intelligently managed. The effectiveness of the system's thermal solution can be monitored using the THERM input. The ADT7473 also provides critical thermal protection to the system using the bidirectional THERM pin as an output to prevent system or component overheating.
FUNCTIONAL BLOCK DIAGRAM
SCL SDA SMBALERT
ADT7473
SERIAL BUS INTERFACE
PWM1 PWM2 PWM3
PWM REGISTERS AND CONTROLLERS (HF AND LF)
ACOUSTIC ENHANCEMENT CONTROL
AUTOMATIC FAN SPEED CONTROL ADDRESS POINTER REGISTER PWM CONFIGURATION REGISTERS INTERRUPT MASKING INTERRUPT STATUS REGISTERS
TACH1 TACH2 TACH3 TACH4
DYNAMIC TMIN CONTROL FAN SPEED COUNTER PERFORMANCE MONITORING
THERM VCC D1+ D1- D2+ D2- VCCP BAND GAP TEMP SENSOR SRC VCC TO ADT7473
THERMAL PROTECTION
INPUT SIGNAL CONDITIONING AND ANALOG MULTIPLEXER
10-BIT ADC
LIMIT COMPARATORS
GND
Figure 1.
Rev. A
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.
04686-001
BAND GAP REFERENCE
VALUE AND LIMIT REGISTERS
ADT7473 TABLE OF CONTENTS
Features .............................................................................................. 1 General Description ......................................................................... 1 Functional Block Diagram .............................................................. 1 Specifications..................................................................................... 4 Timing Diagram ........................................................................... 5 Absolute Maximum Ratings............................................................ 6 Thermal Resistance ...................................................................... 6 ESD Caution.................................................................................. 6 Pin Configuration and Function Descriptions............................. 7 Typical Performance Characteristics ............................................. 8 Product Description....................................................................... 10 Comparison Between ADT7467 and ADT7473 .................... 10 How to Set the Functionality of Pin 9...................................... 10 Recommended Implementation............................................... 10 Serial Bus Interface..................................................................... 11 Write Operations ........................................................................ 12 Read Operations ......................................................................... 13 SMBus Timeout .......................................................................... 13 Voltage Measurement Input...................................................... 13 Analog-to-Digital Converter .................................................... 13 Input Circuitry............................................................................ 13 Voltage Measurement Registers................................................ 13 VCCP Limit Registers ................................................................... 14 Additional ADC Functions for Voltage Measurements ........ 14 Temperature Measurement Method ........................................ 15 Series Resistance Cancellation.................................................. 17 Factors Affecting Diode Accuracy ........................................... 17 Additional ADC Functions for Temperature Measurement 19 Limits, Status Registers, and Interrupts....................................... 20 Limit Values ................................................................................ 20 Interrupt Status Registers .......................................................... 21 THERM Timer ........................................................................... 23 Fan Presence Detect................................................................... 31 Sleep States .................................................................................. 31 XNOR Tree Test Mode .............................................................. 31 Power-On Default ...................................................................... 31 Programming the Automatic Fan Speed Control Loop ............ 33 Automatic Fan Control Overview............................................ 33 Step 1: Hardware Configuration .............................................. 34 Step 2: Configuring the Mux .................................................... 36 Step 3: TMIN Settings for Thermal Calibration Channels ...... 38 Step 4: PWMMIN for Each PWM (Fan) Output ...................... 40 Step 5: PWMMAX for PWM (Fan) Outputs.............................. 40 Step 6: TRANGE for Temperature Channels................................ 41 Step 7: TTHERM for Temperature Channels ............................... 44 Step 8: THYST for Temperature Channels.................................. 45 Dynamic TMIN Control Mode ................................................... 47 Step 9: Operating Points for Temperature Channels............. 49 Step 10: High and Low Limits for Temperature Channels ... 50 Step 11: Monitoring THERM ................................................... 52 Enhancing System Acoustics .................................................... 53 Step 12: Ramp Rate for Acoustic Enhancement..................... 55 Register Tables ................................................................................ 58 Outline Dimensions ....................................................................... 76 Ordering Guide .......................................................................... 76
Rev. A | Page 2 of 76
ADT7473
REVISION HISTORY
2/06--Rev. 0 to Rev. A. Changes to Table 1 ............................................................................4 Change to Table 3 ..............................................................................6 Changes to Comparisons Between the ADT7467 and ADT7476 section .....................................................................10 Changes to SMBALERT Interrupt Behavior Section .................21 Changes to Interrupt Mask Register 1 (0x74) Section ...............22 Changes to Fan Drive Using PWM Control................................26 Changes to Reading Fan Speed from the ADT7473...................28 Changes to Ordering Guide...........................................................76 6/05--Revision 0: Initial Version
Rev. A | Page 3 of 76
ADT7473 SPECIFICATIONS
TA = TMIN to TMAX, VCC = VMIN to VMAX, unless other wise 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 0.25 6 36 96 Max 3.6 3 1.5 2.5 1.5 2.5 Unit V mA C C C C C C A A Test Conditions/Comments
Interface inactive, ADC active 0C TA 85C -40C TA 125C 0C TA 85C -40C TA +125C First current Second current Third current
ANALOG-TO-DIGITAL CONVERTER (INCLUDING MUX AND ATTENTUATORS) 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 Input Resistance FAN RPM-TO-DIGITAL CONVERTER Accuracy Full-Scale Count Nominal Input RPM 70
1.5 1 0.1 11 12 38 145 19 120 6 10 65,535 109 329 5,000 10,000
% LSB %/V ms ms ms ms ms k % % RPM RPM RPM RPM
8 bits Averaging enabled Averaging enabled Averaging enabled Averaging enabled Averaging disabled For VCCP channel 0C TA 70C -40C TA +120C Fan count = 0xBFFF Fan count = 0x3FFF Fan count = 0x0438 Fan count = 0x021C
OPEN-DRAIN DIGITAL OUTPUTS, PWM1 TO PWM3, XTO Current Sink, IOL Output Low Voltage, VOL High Level Output Current, IOH OPEN-DRAIN SERIAL DATA BUS OUTPUT (SDA) Output Low Voltage, VOL High Level Output Current, IOH SMBus DIGITAL INPUTS (SCL, SDA) Input High Voltage, VIH Input Low Voltage, VIL Hysteresis
0.1
8.0 0.4 20 0.4 1.0
mA V A V A V V mV
IOUT = -8.0 mA VOUT = VCC IOUT = -4.0 mA VOUT = VCC
0.1 2.0
0.4 500
Rev. A | Page 4 of 76
ADT7473
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
3.6 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 noted. Typicals are at TA = 25C and represent most likely parametric norm. Logic inputs accept input high voltages up to VMAX, even when device is operating down to VMIN. Timing specifications are tested at logic levels of VIL = 0.8 V for a falling edge and VIH = 2.0 V for a rising edge.
TIMING DIAGRAM
Serial management bus (SMBus) timing specifications are guaranteed by design and are not production tested.
tLOW
SCL
tR
tF
tHD; STA
tHD; STA
tHD; DAT
tHIGH
tSU; DAT
tSU; STA
tSU; STO
SDA P
tBUF
S
S
P
Figure 2. Serial Bus Timing Diagram
Rev. A | Page 5 of 76
04686-002
ADT7473 ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Positive Supply Voltage (VCC) Voltage on Any Input or Output Pin Input Current at Any Pin Package Input Current Maximum Junction Temperature (TJ max) Storage Temperature Range Lead Temperature, Soldering IR Reflow Peak Temperature Lead Temperature (Soldering, 10 sec) ESD Rating Rating 3.6 V -0.3 V to +3.6 V 5 mA 20 mA 150C -65C to +150C 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 RESISTANCE
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 16-Lead QSOP JA 150 JC 39 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. A | Page 6 of 76
ADT7473 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
SCL 1 GND 2 VCC 3 TACH3 4 PWM2/SMBALERT 5 TACH1 6 TACH2 7 PWM3 8
16 SDA 15 PWM1/XTO 14 VCCP 13 D1+ TOP VIEW (Not to Scale) 12 D1- 11 D2+ 10 D2- 9
ADT7473
TACH4/GPIO/THERM/SMBALERT
Figure 3. Pin Configuration
Table 4. Pin Function Descriptions
Pin No. 1 2 3 4 5 Mnemonic SCL GND VCC TACH3 PWM2 SMBALERT 6 7 8 9 TACH1 TACH2 PWM3 TACH4 GPIO THERM Description Digital Input (Open Drain). SMBus serial clock input. Requires SMBus pull-up. Ground Pin for the ADT7473. Power Supply. Powered by 3.3 V. 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). Can be reconfigured as an SMBALERT interrupt output to signal out-of-limit conditions. Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 1. 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. Digital Input (Open Drain). Fan tachometer input to measure speed of Fan 4. General-Purpose Open Drain Digital I/O. Bidirectional THERM pin. Can be used to time and monitor assertions on the THERM input as well as to assert when an ADT7473 THERM overtemperature limit is exceeded. For example, the pin can be connected to the PROCHOT output of an Intel 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-of-limit conditions. Cathode Connection to Second Thermal Diode. Anode Connection to Second Thermal Diode. Cathode Connection to First Thermal Diode. Anode Connection to First Thermal Diode. Analog Input. Monitors processor core voltage (0 V to 3 V). Digital Output (Open Drain). Pulse-width modulated output to control Fan 1 speed. Requires 10 k typical pull-up. Also functions as the output from the XNOR tree in XNOR test mode. Digital I/O (Open Drain). SMBus bidirectional serial data. Requires 10 k typical pull-up.
SMBALERT 10 11 12 13 14 15 16 D2- D2+ D1- D1+ VCCP PWM1 XTO SDA
Rev. A | Page 7 of 76
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ADT7473 TYPICAL PERFORMANCE CHARACTERISTICS
60 70 60
TEMPERATURE ERROR (C)
40
TEMPERATURE ERROR (C)
50 40 30 100mV 20 40mV 10
04686-008
20 D+ TO GND 0 D+ TO VCC
-20
60mV
-40
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0 -10
-60 0 10 20 30 40 50 60 70 80 90 LEAKAGE RESISTANCE (M)
100
0
100M
200M
300M
400M
500M
600M
NOISE FREQUENCY (Hz)
Figure 4. Remote Temperature Error vs. PCB Resistance
Figure 7. Remote Temperature Error vs. Common-Mode Noise Frequency
0
1.20 1.18
-10
TEMPERATURE ERROR (C)
1.16 1.14
-20
IDD (mA)
1.12 1.10 1.08 1.06 1.04
-30
-40
-50
04686-006
1.02 1.00 0.98 3.0 3.1 3.2 3.3 VDD (V) 3.4 3.5 3.6
04686-009
-60 0 2 4 6 8 10 12 14 16 18 20 22 CAPACITANCE (nF)
Figure 5. Temperature Error vs. Capacitance Between D+ and D-
Figure 8. Normal IDD vs. Power Supply
30 25
TEMPERATURE ERROR (C)
15
100mV
TEMPERATURE ERROR (C)
10
20 15 10 5 0 40mV -5 0 100M 200M 300M 400M 500M NOISE FREQUENCY (Hz)
5
100mV
60mV
0 250mV
-5
-10
04686-007
04686-010
-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. Frequency
Rev. A | Page 8 of 76
ADT7473
6 4
3.0 2.5
250mV
TEMPERATURE ERROR (C)
TEMPERATURE ERROR (C)
2 0 -2 100mV -4 -6 -8
04686-011
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)
04686-013
-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. Temperature
3.0 2.5
TEMPERATURE ERROR (C)
2.0 1.5 1.0 0.5 0 -0.5
04686-012
-1.0 -1.5 -40 -20 0 20 40 60 85 105 125 OIL BATH TEMPERATURE (C)
Figure 11. Internal Temperature Error vs. Temperature
Rev. A | Page 9 of 76
ADT7473 PRODUCT DESCRIPTION
The ADT7473 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 16), and an input line for the serial clock (Pin 1). All control and programming functions for the ADT7473 are performed over the serial bus. Additionally, a pin can be reconfigured as an SMBALERT output to signal out-of-limit conditions.
HOW TO SET THE FUNCTIONALITY OF PIN 9
Pin 9 on the ADT7473 has four possible functions: SMBALERT, THERM, GPIO, and TACH4. The user chooses the required functionality by setting Bit 0 and Bit 1 of Configuration Register 4 (0x7D). Table 5. Pin 9 Settings
Bit 0 0 0 1 1 Bit 1 0 1 0 1 Function TACH4 THERM SMBALERT GPIO
COMPARISON BETWEEN ADT7467 AND ADT7473
The following list shows some comparisons between the ADT7467 and the ADT7473: * The ADT7473 can be powered via a 3.3 V supply only, and does not support 5 V operation, while the ADT7467 does. Violating this specification results in irreversible damage to the ADT7473. See the ADT7473 Specifications section for more information. High frequency PWM drive can be independently selected for each PWM channel on the ADT7473. This is not available on the ADT7467. The range and resolution of the temperature offset register can be changed from a 64C range at 0.5C resolution to a 128C range at 1C resolution. This is not available on the ADT7467. THERM overtemperature events can be disabled/enabled individually on each temperature channel. This is not available on the ADT7467. Bit 7 of Configuration Register 1 is no longer supported because the ADT7473 cannot be powered via a 5 V supply. Bit 0 of Configuration Register 1 (0x40) remains writable after the lock bit is set. This bit enables monitoring. 2-wire fan speed measurement is not supported on the ADT7473.
ADT7473
FRONT CHASSIS FAN
RECOMMENDED IMPLEMENTATION
Configuring the ADT7473, 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 3. CPU temperature measured using Remote 1 temperature channel. Ambient temperature measured through Remote 2 temperature channel. Bidirectional THERM pin. This feature allows Intel Pentium 4 PROCHOT monitoring and can function as an overtemperature THERM output. It can alternatively be programmed as an SMBALERT system interrupt output.
*
*
*
* * *
CPU FAN PWM1
TACH2
TACH1
REAR CHASSIS FAN
PWM3 TACH3 D2+ D2- THERM PROCHOT CPU
AMBIENT TEMPERATURE
D1+ D1- SDA SCL SMBALERT
04686-015
GND
ICH
Figure 13. ADT7473 Configuration
Rev. A | Page 10 of 76
ADT7473
SERIAL BUS INTERFACE
On PCs and servers, control of the ADT7473 is carried out using the SMBus. The ADT7473 is connected to this bus as a slave device, under the control of a master controller, which is usually (but not necessarily) the ICH. The ADT7473 has a fixed 7-bit serial bus address of 0101110 or 0x2E. The read/write bit must be added to get the 8-bit address (01011100 or 0x5C). Data is sent over the serial bus in sequences of nine clock pulses: eight bits of data followed by an acknowledge bit from the slave device. Transitions on the data line must occur during the low period of the clock signal and remain stable during the high period, because a low-to-high transition when the clock is high might be interpreted as a stop signal. The number of data bytes that can be transmitted over the serial bus in a single read or write operation is limited only by what the master and slave devices can handle. When all data bytes have been read or written, stop conditions are established. In write mode, the master pulls the data line high during the tenth clock pulse to assert a stop condition. In read mode, the master device overrides the acknowledge bit by pulling the data line high during the low period before the ninth clock pulse; this is known as No Acknowledge. The master takes the data line low during the low period before the tenth clock pulse, and then high during the tenth clock pulse to assert a stop condition. Any number of bytes of data can be transferred over the serial bus in one operation, but it is not possible to mix read and write in one operation, because the type of operation is determined at the beginning and cannot subsequently be changed without starting a new operation. In the ADT7473, 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, and then data can be written into that register or read from it. The first byte of a write operation always contains an address that is stored in the address pointer register. If data is written to the device, the write operation contains a second data byte that is written to the register selected by the address pointer register. This write operation is shown in Figure 14. The device address is sent over the bus, and then R/W is set to 0. This is followed by two data bytes. The first data byte is the address of the internal data register to be written to, which is stored in the address pointer register. The second data byte is the data to be written to the internal data register. When reading data from a register, there are two possibilities: * If the ADT7473's address pointer register value is unknown or not the desired value, it must first be set to the correct value before data can be read from the desired data register. This is done by performing a write to the ADT7473, but only the data byte containing the register address is sent, because no data is written to the register. This is shown in Figure 15. A read operation is then performed consisting of the serial bus address, R/W bit set to 1, followed by the data byte read from the data register. This is shown in Figure 16. * If the address pointer register is known to be already at the desired address, data can be read from the corresponding data register without first writing to the address pointer register, as shown in Figure 16.
9
1 SCL
9
1
SDA START BY MASTER
0
1
0
1
1
1
0
R/W ACK. BY ADT7473
D7
D6
D5
D4
D3
D2
D1
D0 ACK. BY ADT7473
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 ADT7473 MASTER
Figure 14. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register
Rev. A | Page 11 of 76
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FRAME 3 DATA BYTE
ADT7473
1 SCL 9 1 9
SDA START BY MASTER
0
1
0
1
1
1
0
R/W ACK. BY ADT7473
D7
D6
D5
D4
D3
D2
D1
D0
04686-017
04686-018
FRAME 1 SERIAL BUS ADDRESS BYTE
FRAME 2 ADDRESS POINTER REGISTER BYTE
ACK. BY ADT7473
STOP BY MASTER
Figure 15. Writing to the Address Pointer Register Only
1 SCL 9 1 9
SDA START BY MASTER
0
1
0
1
1
1
0
R/W ACK. BY ADT7473
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 ADT7473
Figure 16. Reading Data from a Previously Selected Register
SLAVE S WA ADDRESS
REGISTER ADDRESS
AP
In addition to supporting the send byte and receive byte protocols, the ADT7473 also supports the read byte protocol. (See System Management Bus Specifications Rev. 2 for more information; this document is available from Intel.) If several read or write operations must be performed in succession, the master can send a repeat start condition instead of a stop condition to begin a new operation.
Figure 17. Setting a Register Address for Subsequent Read
If the master is required to read data from the register immediately after setting up the address, it can assert a repeat start condition immediately after the final ACK and carry out a single-byte read without asserting an intermediate stop condition.
Write Byte
In this operation, the master device sends a command byte and one data byte to the slave device, as follows: 1. 2. 3. 4. 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 (active 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.
WRITE OPERATIONS
The SMBus specification defines several protocols for various read and write operations. The ADT7473 uses the following SMBus write protocols. The following abbreviations are used in the diagrams: S - START P - STOP R - READ W - WRITE A - ACKNOWLEDGE A - NO ACKNOWLEDGE
Send Byte
In this operation, the master device sends a single command byte to a slave device, as follows: 1. The master device asserts a start condition on SDA. 2. The master sends the 7-bit slave address followed by the write bit (active low). 3. The addressed slave device asserts ACK on SDA. 4. The master sends a command code. 5. The slave asserts ACK on SDA. 6. The master asserts a stop condition on SDA and the transaction ends.
The single byte write operation is illustrated in Figure 18.
1 2 3 4 REGISTER ADDRESS 5 A 6 DATA 78 AP
04686-020
SLAVE S ADDRESS W A
Figure 18. Single-Byte Write to a Register
Rev. A | Page 12 of 76
04686-019
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.
For the ADT7473, 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 17.
1 2 3 4 56
ADT7473
READ OPERATIONS
The ADT7473 uses the following SMBus read protocols. Once the ADT7473 has responded to the alert response address, the master must read the status registers, and the SMBALERT is cleared only if the error condition is gone.
Receive Byte
This operation is useful when repeatedly reading a single register. The register address must have been previously set up. In this operation, the master device receives a single byte from a slave device, as follows: 1. 2. 3. 4. 5. 6. The master device asserts a start condition on SDA. The master sends the 7-bit slave address followed by the read bit (high). The addressed slave device asserts ACK on SDA. The master receives a data byte. The master asserts NO ACK on SDA. The master asserts a stop condition on SDA, and the transaction ends.
SMBus TIMEOUT
The ADT7473 includes an SMBus timeout feature. If there is no SMBus activity for 35 ms, the ADT7473 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 work with the SMBus timeout feature, so it can be disabled.
Configuration Register 1 (0x40)
Bit 6 TODIS = 0; SMBus timeout enabled (default) Bit 6 TODIS = 1; SMBus timeout disabled
VOLTAGE MEASUREMENT INPUT
The ADT7473 has one external voltage measurement channel and can also measure its own supply voltage, VCC. Pin 14 can measure VCCP. The VCC supply voltage measurement is carried out through the VCC pin (Pin 3). The VCCP input can be used to monitor a chipset supply voltage in computer systems.
In the ADT7473, 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 19.
1 2 3 4 DATA 56 AP
04686-021
ANALOG-TO-DIGITAL CONVERTER
All analog inputs are multiplexed into the on-chip, successive approximation, analog-to-digital converter. This has a resolution of 10 bits. The basic input range is 0 V to 2.25 V, but the input has built-in attenuators to allow measurement of VCCP without any external components. To allow for the tolerance of the supply voltage, the ADC produces an output of 3/4 full scale (768 decimal or 300 hex) for the nominal input voltage and thus has adequate headroom to deal with overvoltages.
SLAVE S ADDRESS R A
Figure 19. Single-Byte Read from a Register
Alert Response Address
Alert response address (ARA) is a feature of SMBus devices that allows an interrupting device to identify itself to the host when multiple devices exist on the same bus. The SMBALERT output can be used as either an interrupt output or an SMBALERT. One or more outputs can be connected to a common SMBALERT line connected to the master. If a device's SMBALERT line goes low, the following events occur: * * SMBALERT is pulled low.
INPUT CIRCUITRY
The internal structure for the VCCP analog input is shown in Figure 20. The input circuit consists of an input protection diode, an attenuator, plus a capacitor to form a first order low-pass filter that gives the input immunity to high frequency noise.
VCCP 17.5k 52.5k 35pF
The master initiates a read operation and sends the alert response address (ARA = 0001 100). This is a general call address that must not be used as a specific device address. The device whose SMBALERT output is low responds to the alert response address, and the master reads its device address. The address of the device is now known and can be interrogated in the usual way. If more than one device's SMBALERT output is low, the one with the lowest device address has priority in accordance with normal SMBus arbitration.
Figure 20. Structure of Analog Inputs
*
VOLTAGE MEASUREMENT REGISTERS
Register 0x21 VCCP Reading = 0x00 default Register 0x22 VCC Reading = 0x00 default
*
Rev. A | Page 13 of 76
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ADT7473
VCCP LIMIT REGISTERS
Associated with the VCCP 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 0x46 VCCP Low Limit = 0x00 default Register 0x47 VCCP High Limit = 0xFF default Table 7 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 711 s and averages 16 conversions to reduce noise; a measurement takes nominally 11.38 ms.
Bypass Voltage Input Attenuator
Setting Bit 5 of Configuration Register 2 (0x73) removes the attenuation circuitry from the VCCP input. This allows the user to directly connect external sensors or to rescale the analog voltage measurement inputs for other applications. The input range of the ADC without the attenuators is 0 V to 2.25 V.
Single-Channel ADC Conversion
Setting Bit 6 of Configuration Register 2 (0x73) places the ADT7473 into single-channel ADC conversion mode. In this mode, the ADT7473 can be made to read a single voltage channel only. If the internal ADT7473 clock is used, the selected input is read every 711 s. The appropriate ADC channel is selected by writing to Bits [7:5] of the TACH1 minimum high byte register (0x55). Table 6. Programming Single-Channel ADC Mode
Bits [7:5] Reg. 0x55 001 010 101 110 111 Channel Selected VCCP VCC Remote 1 temperature Local temperature Remote 2 temperature
ADDITIONAL ADC FUNCTIONS FOR VOLTAGE MEASUREMENTS
A number of other functions are available on the ADT7473 to offer the system designer increased flexibility.
Turn-Off Averaging
For each voltage measurement read from a value register, 16 readings have actually been made internally and the results averaged before being placed into the value register. When faster conversions are needed, setting Bit 4 of Configuration Register 2 (0x73) turns averaging off. This effectively gives a reading 16 times faster (711 s), but the reading may be noisier.
Configuration Register 2 (0x73)
Bit 4 = 1; averaging off. Bit 5 = 1; bypass input attenuators. Bit 6 = 1; single-channel convert mode.
TACH1 Minimum High Byte Register (0x55)
Bits [7:5] select ADC channel for single-channel convert mode.
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ADT7473
Table 7. 10-Bit ADC Output Codes vs. VIN
VCC (3.3 VIN)1 <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 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 ADC Output Decimal 0 1 2 3 4 5 6 7 8 * * * 256 (1/4 scale) * * * 512 (1/2 scale) * * * 768 (3/4 scale) * * * 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 Binary (10 Bits) 00000000 00 00000000 01 00000000 10 00000000 11 00000001 00 00000001 01 00000001 10 00000001 11 00000010 00
1.100 to 1.1042
0.7500 to 0.7529
01000000 00
2.200 to 2.2042
1.5000 to 1.5029
10000000 00
3.300 to 3.3042
2.2500 to 2.2529
11000000 00
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
1
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
11111101 01 11111101 10 11111101 11 11111110 00 11111110 01 11111110 10 11111110 11 11111111 00 11111111 01 11111111 10 11111111 11
The VCC output codes listed assume that VCC is 3.3 V.
TEMPERATURE MEASUREMENT METHOD
A simple method of measuring temperature is to exploit the negative temperature coefficient of a diode, measuring the baseemitter voltage (VBE) of a transistor operated at constant current. Unfortunately, this technique requires calibration to null out the effect of the absolute value of VBE, which varies from device to device. The technique used in the ADT7473 is to measure the change in VBE when the device is operated at three different currents. Previous devices have used only two operating currents, but the use of a third current allows automatic cancellation of resistances in series with the external temperature sensor.
Figure 21 shows the input signal conditioning used to measure the output of an external temperature sensor. This figure shows the external sensor as a substrate transistor, but it could equally be a discrete transistor. If a discrete transistor is used, the collector is not grounded and should be linked to the base. To prevent ground noise from interfering with the measurement, the more negative terminal of the sensor is not referenced to ground, but is biased above ground by an internal diode at the D- input. C1 can optionally be added as a noise filter (recommended maximum value 1000 pF). However, a better option in noisy environments is to add a filter, as described in the Noise Filtering section.
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ADT7473
Local Temperature Measurement
The ADT7473 contains an on-chip band gap temperature sensor whose output is digitized by the on-chip 10-bit ADC. The 8-bit MSB temperature data is stored in the local temperature register (0x26). 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 8 and Table 9. Theoretically, the temperature sensor and ADC can measure temperatures from -63C to +127C (or -63C 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 ADT7473 operating temperature range are not possible. Table 8. Twos Complement Temperature Data Format
Temperature -128C -63C -50C -25C -10C 0C 10.25C 25.5C 50.75C 75C 100C 125C 127C
1
Remote Temperature Measurement
The ADT7473 can measure the temperature of two remote diode sensors or diode-connected transistors connected to Pin 10 and Pin 11, or Pin 12 and Pin 13. The forward voltage of a diode or diode-connected transistor operated at a constant current exhibits a negative temperature coefficient of about -2 mV/C. Unfortunately, the absolute value of VBE varies from device to device and individual calibration is required to null this out, so the technique is unsuitable for mass production. The technique used in the ADT7473 is to measure the change in VBE when the device is operated at three different currents. This is given by
V BE = KT / q x 1n(N ) where: K is Boltzmann's constant. q is the charge on the carrier. T is the absolute temperature in Kelvin. N is the ratio of the two currents. Figure 21 shows the input signal conditioning used to measure the output of a remote temperature sensor. This figure shows the external sensor as a substrate transistor, provided for temperature monitoring on some microprocessors. It could also be a discrete transistor such as a 2N3904/2N3906.
VDD I N2 x I N1 x I IBIAS
Digital Output (10-Bit)1 1000 0000 00 (diode fault) 1100 0001 00 1100 1110 00 1110 0111 00 1111 0110 00 0000 0000 00 0000 1010 01 0001 1001 10 0011 0010 11 0100 1011 00 0110 0100 00 0111 1101 00 0111 1111 00
Bold numbers denote 2 LSBs of measurement in Extended Resolution Register 2 (0x77) with 0.25C resolution.
REMOTE SENSING TRANSISTOR D+ D-
LPF
VOUT+ TO ADC
Temperature -64C -63C -1C 0C 1C 10C 25C 50C 75C 100C 125C 191C
1
Digital Output (10-Bit)1 0000 0000 00 (diode fault) 0000 0001 00 0011 1111 00 0100 0000 00 0100 0001 00 0100 1010 00 0101 1001 00 0111 0010 00 1000 1001 00 1010 0100 00 1011 1101 00 1111 1111 00
Figure 21. Signal Conditioning for Remote Diode Temperature Sensors
If a discrete transistor is used, the collector is not grounded and should be linked to the base. If a PNP transistor is used, the base is connected to the D- input and the emitter is connected to the D+ input. If an NPN transistor is used, the emitter is connected to the D- input and the base is connected to the D+ input. Figure 22 and Figure 23 show how to connect the ADT7473 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.
Bold numbers denote 2 LSBs of measurement in Extended Resolution Register 2 (0x77) with 0.25C resolution.
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Table 9. Extended Range, Temperature Data Format
fC = 65kHz
VOUT-
ADT7473
ADT7473
2N3904 NPN D+
04686-025
The construction of a filter allows the ADT7473 and the remote temperature sensor to operate in noisy environments. Figure 24 shows a low-pass R-C filter with the following values: R = 100 , C = 1 nF This filtering reduces both common-mode noise and differential noise.
100 REMOTE TEMPERATURE SENSOR
04686-026
D-
Figure 22. Measuring Temperature Using an NPN Transistor
ADT7473
D+ 2N3906 PNP D-
D+
04686-024
1nF 100 D-
Figure 24. Filter Between Remote Sensor and ADT7473
Figure 23. Measuring Temperature Using a PNP Transistor
SERIES RESISTANCE CANCELLATION
Parasitic resistance to the ADT7473 D+ and D- inputs (seen in series with the remote diode) is caused by a variety of factors including PCB track resistance and track length. This series resistance appears as a temperature offset in the remote sensor's temperature measurement. This error typically causes a 0.5C offset per of parasitic resistance in series with the remote diode. The ADT7473 automatically cancels out the effect of this series resistance on the temperature reading, giving a more accurate result without the need for user characterization of this resistance. The ADT7473 is designed to automatically cancel up to 3 k of resistance, typically. This is transparent to the user by using an advanced temperature measurement method. This feature allows resistances to be added to the sensor path to produce a filter, allowing the part to be used in noisy environments. See the Noise Filtering section for details.
To measure VBE, the operating current through the sensor is switched among three related currents. N1 x I and N2 x I are different multiples of the current I, as shown in Figure 21. The currents through the temperature diode are switched between I and N1 x I, giving VBE1, and then between I and N2 x I, giving VBE2. The temperature can then be calculated using the two VBE measurements. This method can also cancel the effect of any series resistance on the temperature measurement. The resulting VBE waveforms are passed through a 65 kHz low-pass filter to remove noise and then to a chopper-stabilized amplifier. This amplifies and rectifies the waveform to produce a dc voltage proportional to VBE. The ADC digitizes this voltage, and a temperature measurement is produced. To reduce the effects of noise, digital filtering is performed by averaging the results of 16 measurement cycles. The results of remote temperature measurements are stored in 10-bit, twos complement format, as listed in Table 8. 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.
FACTORS AFFECTING DIODE ACCURACY
Remote Sensing Diode
The ADT7473 is designed to work with either substrate transistors built into processors or 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 is connected 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 ADT7473 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. Refer to the data sheet for the related CPU to obtain the nf values.
T = (nf - 1.008)/1.008 x (273.15 K + T)
Noise Filtering
For temperature sensors operating in noisy environments, previous practice was to place 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, making use of the sensor difficult in a very noisy environment. The ADT7473 has a major advantage over other devices for eliminating the effects of noise on the external sensor. Using the series resistance cancellation feature, a filter can be constructed between the external temperature sensor and the part. The effect of any filter resistance seen in series with the remote sensor is automatically canceled from the temperature result.
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ADT7473
To factor this in, the user can write the T value to the offset register. Then, the ADT7473 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 ADT7473, IHIGH, is 96 A and the low level current, ILOW, is 6 A. If the ADT7473 current levels do not match the current levels specified by the CPU manufacturer, it might 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, the algebraic sum of these offsets must be programmed to the offset register. If a discrete transistor is used with the ADT7473, the best accuracy is obtained by choosing devices according to the following criteria: * * * * Base-emitter voltage greater than 0.25 V at 6 A, at the highest operating temperature Base-emitter voltage less than 0.95 V at 100 A, at the lowest operating temperature Base resistance less than 100 Small variation in hFE (such as 50 to 150) that indicates tight control of VBE characteristics
ADT7460/ADT7473 Backwards-Compatible Mode
By setting Bit 1 of Configuration Register 5 (0x7C), all temperature measurements are stored in the zone temperature value registers (Register 0x25, Register 0x26, and Register 0x27) in twos complement, in the range -63C to +127C. (The ADT7473 still makes calculations based on the Offset 64 extended range and clamps the results, if necessary.) The temperature limits must be reprogrammed in twos complement. If a twos complement temperature below -63C is entered, the temperature is clamped to -63C. In this mode, the diode fault condition remains -128C = 1000 0000, while in the extended temperature range (-64C to +191C), the fault condition is represented by -64C = 0000 0000.
Temperature Measurement Registers
Register 0x25, Remote 1 Temperature Register 0x26, Local Temperature Register 0x27, Remote 2 Temperature Register 0x77, Extended Resolution 2 = 0x00 default Bits [7:6] TDM2, Remote 2 temperature LSBs Bits [5:4] LTMP, local temperature LSBs Bits [3:2] TDM1, Remote 1 temperature LSBs
Temperature Measurement 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. Register 0x4E, Remote 1 Temperature Low Limit = 0x01 default Register 0x4F, Remote 1 Temperature High Limit = 0x7F default Register 0x50, Local Temperature Low Limit = 0x01 default Register 0x51, Local Temperature High Limit = 0x7F default Register 0x52, Remote 2 Temperature Low Limit = 0x01 default Register 0x53, Remote 2 Temperature High Limit = 0x7F default
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 becomes 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 ADT7473 has temperature offset registers at Register 0x70 and Register 0x72 for the Remote 1 and Remote 2 temperature channels. By performing 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. The LSBs add +0.5C offset to the temperature reading so the 8-bit register effectively allows temperature offsets of up to 64C with a resolution of +0.5C. This ensures that the readings in the temperature measurement registers are as accurate as possible.
Reading Temperature from the ADT7473
It is important to note that the temperature can be read from the ADT7473 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, a 2-register read for each measurement is used. The extended resolution register (Register 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.
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)
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ADT7473
ADDITIONAL ADC FUNCTIONS FOR TEMPERATURE MEASUREMENT
A number of other functions are available on the ADT7473 to offer the system designer increased flexibility.
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 limits. When a temperature exceeds its THERM limit, all PWM outputs run at 100% duty cycle or the maximum PWM duty cycle (Register 0x38, Register 0x39, and Register 0x3A) if Bit 3 of Configuration Register 4 (0x7D) is set. The fans remain running at this speed until the temperature drops below THERM minus hysteresis; this can be disabled by setting the boost bit in Configuration Register 3 (0x78), Bit 2. The hysteresis value for that THERM limit is the value programmed into the hysteresis registers (Register 0x6D and Register 0x6E). The default hysteresis value is 4C.
THERM LIMIT
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.
Table 10. Conversion Time with Averaging Disabled
Channel Voltage Channel Remote 1 Temperature Remote 2 Temperature Local Temperature Channel Voltage Channels Remote Temperature Local Temperature Measurement Time 0.7 ms 7 ms 7 ms 1.3 ms Measurement Time 11 ms 39 ms 12 ms
Table 11. Conversion Time with Averaging Enabled
TEMPERATURE
HYSTERESIS (C)
Single-Channel ADC Conversions
Setting Bit 6 of Configuration Register 2 (0x73) places the ADT7473 into single-channel ADC conversion mode. In this mode, the ADT7473 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 12. Programming Single-Channel ADC Mode for Temperatures
Bits [7:5] Register 0x55 101 110 111 Channel Selected Remote 1 temperature Local temperature Remote 2 temperature
Figure 25. THERM Limit Operation
Configuration Register 2 (0x73)
Bit 4 = 1, averaging off Bit 6 = 1, single-channel convert mode
TACH1 Minimum High Byte Register (0x55)
Bits [7:5] select ADC channel for single-channel convert mode.
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FANS
100%
ADT7473 LIMITS, STATUS REGISTERS, AND INTERRUPTS
LIMIT VALUES
Associated with each measurement channel on the ADT7473 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 a processor or microcontroller of out-of-limit conditions.
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
8-Bit Limits
The following is a list of 8-bit limits on the ADT7473.
Voltage Limit Registers
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
Temperature Limit Registers
Out-of-Limit Comparisons
Once all limits have been programmed, the ADT7473 can be enabled for monitoring. The ADT7473 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.
Register 0x4E, Remote 1 Temperature Low Limit = 0x01 default Register 0x4F, Remote 1 Temperature High Limit = 0xFF default Register 0x6A, Remote 1 THERM Limit = 0xA4 default Register 0x50, Local Temperature Low Limit = 0x01 default Register 0x51, Local Temperature High Limit = 0xFF default Register 0x6B, Local THERM Temperature Limit = 0xA4 default Register 0x52, Remote 2 Temperature Low Limit = 0x01 default Register 0x53, Remote 2 Temperature High Limit = 0xFF default Register 0x6C, Remote 2 THERM Temperature Limit = 0xA4 default
THERM Limit Register
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). By default, the ADT7473 powers up with this bit set. The ADC measures each analog input in turn and, as each measurement is completed, the result is automatically stored in the appropriate value register. This round-robin monitoring cycle continues unless disabled by writing a 0 to Bit 0 of Configuration Register 1. As the ADC is normally left to free-run in this manner, the time taken to monitor all the analog inputs is normally not of interest, because the most recently measured value of any input can be read out at any time. For applications where the monitoring cycle time is important, it can easily be calculated. The total number of channels measured is * * * * One dedicated supply voltage input (VCCP) Supply voltage (VCC pin) Local temperature Two remote temperatures
Register 0x7A, THERM Timer Limit = 0x00 default
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.
Rev. A | Page 20 of 76
ADT7473
As mentioned previously, the ADC performs round-robin conversions. The total monitoring cycle time for averaged voltage and temperature monitoring is 146 ms. The total monitoring cycle time for voltage and temperature monitoring with averaging disabled is 19 ms. The ADT7473 is a derivative of the ADT7467. As a result, the total conversion time in the ADT7473 is the same as the total conversion time of the ADT7467, even though the ADT7473 has fewer monitored channels. Fan TACH measurements are made in parallel and are not synchronized with the analog measurements in any way.
Interrupt Status Register 2 (0x42)
Bit 7 (D2) = 1, indicates an open or short on D2+/D2- inputs. Bit 6 (D1) = 1, indicates an open or short on D1+/D1- inputs. Bit 5 (F4P) = 1, indicates Fan 4 has dropped below the minimum speed. Alternatively, it indicates the THERM limit has been exceeded, if the THERM function is used. Bit 4 (FAN3) = 1, indicates Fan 3 has dropped below the minimum speed. Bit 3 (FAN2) = 1, indicates Fan 2 has dropped below the minimum speed. Bit 2 (FAN1) = 1, indicates Fan 1 has dropped below the minimum speed. Bit 1 (OVT) = 1, indicates a THERM overtemperature limit has been exceeded.
INTERRUPT 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 (Reg. 0x41), a 1 means an out-of-limit event has been flagged in Interrupt Status Register 2. This means the user needs only to read Interrupt Status Register 2 when this bit is set. Alternatively, Pin 5 or Pin 9 can be configured as an SMBALERT output. This 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 (except OVT) 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 (Register 0x74 and Register 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 interrupt status registers. OVT clears automatically.
SMBALERT Interrupt Behavior
The ADT7473 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.
HIGH LIMIT
TEMPERATURE
STICKY STATUS BIT TEMP BACK IN LIMIT (STATUS BIT STAYS SET) SMBALERT
CLEARED ON READ (TEMP BELOW LIMIT)
Figure 26. SMBALERT and Status Bit Behavior
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 2 (VCC) = 1, VCC high or low limit has been exceeded. Bit 1 (VCCP) = 1, VCCP high or low limit has been exceeded.
Figure 26 shows how the SMBALERT output and sticky status bits behave. Once a limit is exceeded, the corresponding status bit is set to 1. The interrupt status bit remains set until the error condition subsides and the interrupt status register is read. The status bits are referred to as sticky because they remain set until read by software. This ensures that an out-of-limit event cannot be missed if software is polling the device periodically. Note that the SMBALERT output remains low for the entire duration that a reading is out of limit and until the interrupt status register has been read. This has implications on how software handles the interrupt. Note: THERM overtemperature events are not sticky, resetting immediately after the overtemperature condition ceases. This also applies to SMBALERT if associated with an OVT event.
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ADT7473
Handling SMBALERT Interrupts
To prevent the system from being tied up servicing interrupts, it is recommended to handle the SMBALERT interrupt as follows: 1. 2. 3. 4. Detect the SMBALERT assertion. Enter the interrupt handler. Read the status registers to identify the interrupt source. Mask the interrupt source by setting the appropriate mask bit in the interrupt mask registers (Register 0x74 and Register 0x75). Take the appropriate action for a given interrupt source. Exit the interrupt handler. Bit 5 (LT) = 1, masks SMBALERT for local temperature. Bit 4 (R1T) = 1, masks SMBALERT for Remote 1 temperature. Bit 2 (VCC) = 1, masks SMBALERT for VCC channel. Bit 1 (VCCP) = 1, masks SMBALERT for VCCP channel.
Interrupt Mask Register 2 (Reg. 0x75)
Bit 7 (D2) = 1, masks SMBALERT for Diode 2 errors. Bit 6 (D1) = 1, masks SMBALERT for Diode 1 errors. Bit 5 (FAN4) = 1, masks SMBALERT for Fan 4 failure. If the TACH4 pin is being used as the THERM input, this bit masks SMBALERT for a THERM event. Bit 4 (FAN3) = 1, masks SMBALERT for Fan 3. Bit 3 (FAN2) = 1, masks SMBALERT for Fan 2.
5. 6.
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 27.
HIGH LIMIT
Bit 2 (FAN1) = 1, masks SMBALERT for Fan 1.
TEMPERATURE
Bit 1 (OVT) = 1, masks SMBALERT for overtemperature (exceeding THERM limits).
CLEARED ON READ (TEMP BELOW LIMIT)
STICKY STATUS BIT
Enabling the SMBALERT Interrupt Output
The SMBALERT interrupt function is disabled by default. Pin 5 or Pin 9 can be reconfigured as an SMBALERT output to signal out-of-limit conditions.
04686-029
TEMP BACK IN LIMIT (STATUS BIT STAYS SET) SMBALERT INTERRUPT MASK BIT SET
INTERRUPT MASK BIT CLEARED (SMBALERT RE-ARMED)
Table 13. Configuring Pin 5 as SMBALERT Output
Register Configuration Register 3 (0x78) Bit Setting [0] ALERT = 1
Figure 27. How Masking the Interrupt Source Affects SMBALERT Output
Masking Interrupt Sources
Register 0x74, Interrupt Mask Register 1 Register 0x75, Interrupt Mask Register 2 These registers allow individual interrupt sources to be masked out to prevent SMBALERT interrupts. Masking an interrupt source prevents only the SMBALERT output from being asserted; the appropriate status bit is set normally.
Assigning THERM Functionality to a Pin
Pin 9 on the ADT7473 has four possible functions: SMBALERT, THERM, GPIO, and TACH4. The user chooses the required functionality by setting Bit 0 and Bit 1 of Configuration Register 4 (0x7D).
Bit1 0 0 1 1 Bit 0 1 0 1 0 Function TACH4 THERM SMBus ALERT GPIO
Interrupt Mask Register 1 (0x74)
Bit 7 (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. Bit 6 (R2T) = 1, masks SMBALERT for Remote 2 temperature
Once Pin 9 is configured as THERM, it must be enabled by setting Bit 1 of Configuration Register 3 (0x78).
THERM as an Input
When THERM is configured as an input, the ADT7473 can time assertions on the THERM pin. This can be useful for connecting to the PROCHOT output of a CPU to gauge system performance. See the THERM Timer section for more information.
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ADT7473
The user can also set up the ADT7473 so that, when the THERM pin is driven low externally, the fans run at 100%. The fans run at 100% for the duration of the time 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, then pulling the THERM low externally has no effect. See Figure 28 for more information.
TMIN
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, then the following happens: 1. 2. The contents of the timer are cleared. Bit 0 of the THERM timer is set to 1 (because a THERM assertion is occurring). The THERM timer increments from 0. If the THERM timer limit (Register 0x7A) = 0x00, the F4P bit is set.
THERM
THERM
3. 4.
THERM ASSERTED TO LOW AS AN INPUT: FANS DO NOT GO TO 100% BECAUSE TEMPERATURE IS BELOW TMIN.
04686-030
THERM ASSERTED TO LOW AS AN INPUT: FANS DO NOT GO TO 100% BECAUSE TEMPERATURE IS ABOVE TMIN AND FANS ARE ALREADY RUNNING.
THERM TIMER (REG. 0x79)
00000001 76543210
THERM ASSERTED 22.76ms
Figure 28. Asserting THERM Low as an Input in Automatic Fan Speed Control Mode
THERM
ACCUMULATE THERM LOW ASSERTION TIMES
THERM TIMER
The ADT7473 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 ADT7473's THERM input and stopped when THERM is deasserted. The timer counts THERM times cumulatively; that is, the timer resumes counting on the next THERM assertion. The THERM timer continues to accumulate THERM assertion times until the timer is read (it is cleared on read) or until it reaches full scale. If the counter reaches full scale, it stops at that reading until cleared. The 8-bit THERM timer 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 becomes the LSB of the timer with a resolution of 22.76 ms (see Figure 29).
THERM TIMER (REG. 0x79)
00000010 76543210 THERM ASSERTED 45.52ms
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 29. Understanding the THERM Timer
Generating SMBALERT Interrupts from THERM Timer Events
The ADT7473 can generate an SMBALERT when a programmable THERM timer limit is 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.
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04686-031
ADT7473
If the THERM timer value exceeds the THERM timer limit value, the F4P bit (Bit 5) of Interrupt Status Register 2 is set and an SMBALERT is generated. The F4P bit (Bit 5) of Interrupt Mask Register 2 (0x75) masks out the SMBALERT if this bit is set to 1; however, the F4P bit of Interrupt Status Register 2 still is set if the THERM timer limit is exceeded. Figure 30 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. Select the desired fan behavior for THERM timer events. Assuming the fans are running, setting Bit 2 (BOOST) 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, the fans do not run at full speed. 3. Select whether THERM timer events should generate SMBALERT interrupts. Bit 5 (F4P) of Interrupt Mask Register 2 (0x75), when set, masks out the SMBALERT when the THERM timer limit value is exceeded. This bit should be cleared if SMBALERT is based on THERM events are required. 4. Select a suitable THERM limit value. This value determines whether an SMBALERT is generated on the first THERM assertion, or only if a cumulative THERM assertion time limit is exceeded. A value of 0x00 causes an SMBALERT to be generated on the first THERM assertion. 5. Select a THERM monitoring time. This value specifies how often OS or BIOS level software checks the THERM timer. For example, BIOS could read the THERM timer once an hour to determine the cumulative THERM assertion time. If, for example, the total THERM assertion time is <22.76 ms in Hour 1, >182.08 ms in Hour 2, and >5.825 sec in Hour 3, this can indicate that system performance is degrading significantly because THERM is asserting more frequently on an hourly basis. Alternatively, OS- or BIOS-level software can timestamp when the system is powered on. If an SMBALERT is generated due to the THERM timer limit being exceeded, another timestamp can be taken. The difference in time 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 seconds to be exceeded and the next time it takes only one hour, this is an indication of a serious degradation in system performance.
Configuring the THERM Behavior
1. Configure Pin 9 as a 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 9 by default. Setting Bit 0 and Bit 1 (PIN9FUNC) of Configuration Register 4 (0x7D) enables THERM timer/output functionality on Pin 9 (Bit 1 of Configuration Register 3, THERM, must also be set). Pin 9 can also be used as TACH4. Setting Bit 5, Bit 6, and Bit 7 of Configuration Register 5 (0x7C) makes THERM bidirectional. This means that if the appropriate temperature channel exceeds the THERM temperature limit, the THERM output asserts. If the ADT7473 is not pulling THERM low, but THERM is pulled low by an external device (such as a CPU overtemperature signal), the THERM timer also times THERM assertions. If Bit 5, Bit 6, and Bit 7 of Configuration Register 5 (0x7C) are set to 0, THERM is set as a timer input only.
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ADT7473
2.914s 1.457s 728.32ms 364.16ms THERM TIMER LIMIT 182.08ms (REGISTER 0x7A) 91.04ms 45.52ms 22.76ms 2.914s 1.457s 728.32ms 364.16ms THERM TIMER 182.08ms (REGISTER 0x79) 91.04ms 45.52ms 22.76ms
01234567
76543210
THERM THERM TIMER CLEARED ON READ
COMPARATOR
IN
OUT LATCH RESET
F4P BIT (BIT 5) INTERRUPT STATUS REGISTER 2
SMBALERT
CLEARED ON READ
1 = MASK
04686-032
F4P BIT (BIT 5) INTERRUPT MASK REGISTER 2 (REGISTER 0x75)
Figure 30. Functional Block Diagram of the ADT7473 THERM Monitoring Circuitry
Configuring the THERM Pin as Bidirectional
In addition to monitoring THERM as an input, the ADT7473 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 Bit 5, Bit 6, and Bit 7 of Configuration Register 5 (0x7C) makes THERM bidirectional for the Remote 1, local, and Remote 2 temperature channels, respectively. Figure 31 shows how the THERM pin asserts low as an output in the event of a critical over temperature.
THERM LIMIT 0.25C THERM LIMIT TEMP
THERM
MONITORING CYCLE
Figure 31. Asserting THERM as an Output, Based on Tripping THERM Limits
An alternative method of disabling THERM is to program the THERM temperature limit to -64C or less in Offset 64 mode, or -128C or less in twos complement mode; that is, for THERM temperature limit values less than -63C or -128C, respectively, THERM is disabled. THERM can also be disabled by setting Bit 1 of Configuration Register 3 (0x78) to 0.
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04686-033
ADT7473
FAN DRIVE USING PWM CONTROL
The ADT7473 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 ADT7473 PWM frequency can be set to a selection of low frequencies or a single high PWM frequency. The low frequency options are usually used for 3-wire fans, while the high frequency option is usually used with 4-wire fans. Note that care must be taken to ensure that the PWM or TACH pins are not connected to a pull-up supply greater than 3.6 V. Many fans have internal pull-ups connected to the TACH/ PWM pins to a supply greater than 3.6 V. Clamping or dividing down the voltage on these pins must be done where necessary. Clamping these pins with a Zener diode can also help prevent back-EMF related noise from being coupled into the system. 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. Typical notebook fans draw a nominal 170 mA; therefore, SOT devices can be used where board space is a concern. In desktops, fans can typically draw 250 mA to 300 mA each. If you drive several fans in parallel from a single PWM output or drive larger server fans, the MOSFET must handle the higher current requirements. The only other stipulation is that the MOSFET have a gate voltage drive, VGS < 3.3 V, for direct interfacing to the PWM output. The MOSFET should also have a low on resistance to ensure that there is not significant voltage drop across the FET, which would reduce the voltage applied across the fan and, therefore, the maximum operating speed of the fan. Figure 32 shows how to drive a 3-wire fan using PWM control.
12V 10k TACH 10k 4.7k 12V FAN 1N4148 3.3V 12V
totem pole TACH output, use one of the input signal conditioning circuits shown in the Fan Speed Measurement section. Figure 33 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.
12V 10k TACH 10k 4.7k TACH 12V FAN 1N4148 12V
ADT7473
3.3V 665
04686-035 04686-036
PWM
Q1 MMBT2222
Figure 33. Driving a 3-Wire Fan Using an NPN Transistor
Because 4-wire fans are powered continuously, the fan speed is not switched on or off as with previous PWM driven/powered fans. This enables it to perform better than 3-wire fans, especially for high frequency applications. Figure 34 shows a typical drive circuit for 4-wire fans. As the PWM input on 4-wire fans is usually internally pulled up to a voltage greater than 3.6 V (the maximum voltage allowed on the ADT7473 PWM output), the PWM output should be clamped to 3.3 V using a Zener diode.
12V 12V 12V, 4-WIRE FAN 10k TACH 10k 4.7k TACH VCC TACH PWM
ADT7473
PWM
ADT7473
3.3V 10k
04686-034
Figure 34. Driving a 4-Wire Fan
Q1 NDT3055L
Driving Two Fans from PWM3
The ADT7473 has four TACH inputs available for fan speed measurement, but only three PWM drive outputs. If a fourth fan is used in the system, it should be driven from the PWM3 output in parallel with the third fan. Figure 35 shows how to drive two fans in parallel using low cost NPN transistors. Figure 36 shows the equivalent circuit using a MOSFET. Because the MOSFET can handle up to 3.5 A, it is simply a matter of connecting another fan directly in parallel with the
PWM
Figure 32. Driving a 3-Wire Fan Using an N-Channel MOSFET
Figure 32 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 3.6 V maximum to prevent damaging the ADT7473. If uncertain as to whether the fan used has an open-collector or
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ADT7473
first. Care should be taken in designing drive circuits with transistors and FETs to ensure the PWM pins are not required to source current and that they sink less than the 8 mA maximum current specified on the data sheet. maximum input signal range is 0 V to 3.6 V. In the event that these inputs are supplied from fan outputs that exceed 0 V to 3.6 V, either resistive attenuation of the fan signal or diode clamping must be included to keep inputs within an acceptable range. Figure 37 to Figure 40 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 37.
VCC 12V
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 35 and Figure 36. The SYNC bit in Register 0x62 enables this function. Synchronization is not required in high frequency mode when used with 4-wire fans.
12V
PULL-UP 4.7k TYPICAL TACH OUTPUT TACH
FAN SPEED COUNTER
04686-039
ADT7473
Figure 37. Fan with TACH Pull-Up to VCC
ADT7473
3.3V
3.3V TACH3 TACH4 3.3V
1k PWM3 2.2k
3.3V Q1 MMBT3904 10k
Q2 MMBT2222
04686-037
10k Q3 MMBT2222
If the fan output has a resistive pull-up to 12 V (or other voltage greater than 3.6 V), the fan output can be clamped with a Zener diode, as shown in Figure 38. The Zener diode voltage should be chosen so that it is greater than VIH of the TACH input but less than 3.6 V, allowing for the voltage tolerance of the Zener. A value of between 3 V and 3.6 V is suitable.
12V VCC
Figure 35. 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
1N4148
PULL-UP 4.7k TYPICAL
TACH OUTPUT
TACH ZD1*
FAN SPEED COUNTER
04686-040
ADT7473
ADT7473
TACH3
*CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8 x VCC
10k TYPICAL TACH 3.3V 3.3V
5V OR 12V FAN
1N4148 TACH
5V OR 12V FAN
Figure 38. Fan with TACH Pull-Up to Voltage > 3.6 V Clamped with Zener Diode
10k TYPICAL PWM3
04686-038
Q1 NDT3055L
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 39.
12V VCC
Figure 36. Interfacing Two Fans in Parallel to the PWM3 Output Using a Single N-Channel MOSFET
Bit [4] (SYNC) of Enhance Acoustics Register 1 (0x62)
SYNC = 1, synchronizes TACH2, TACH3, and TACH4 to PWM3.
PULL-UP 4.7k OR TYPICAL TACH OUTPUT
TACH ZD1 ZENER*
FAN SPEED COUNTER
04686-041
ADT7473
*CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8 x VCC
TACH Inputs
Pin 4, Pin 6, Pin 7, and Pin 9 (when configured as TACH inputs) are open-drain TACH inputs intended for fan speed measurement. Signal conditioning in the ADT7473 accommodates the slow rise and fall times typical of fan tachometer outputs. The
Figure 39. Fan with Strong TACH Pull-Up to > VCC or Totem-Pole Output, Clamped with Zener and Resistor
Alternatively, a resistive attenuator can be used, as shown in Figure 40. R1 and R2 should be chosen such that 2 V < VPULL-UP x R2/(RPULL-UP + R1 + R2) < 3.6 V
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ADT7473
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 120 k and 47 k, respectively. This gives a high input voltage of 3.35 V.
12V VCC
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
<1k
R1* TACH OUTPUT
TACH R2*
FAN SPEED COUNTER
04686-042
Register 0x2E, TACH4 Low Byte = 0x00 default Register 0x2F, TACH4 High Byte = 0x00 default
ADT7473
*SEE TEXT
Reading Fan Speed from the ADT7473
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). Because the device is essentially measuring the fan TACH period, the higher the count value, the slower the fan is actually running. A 16-bit fan tachometer reading of 0xFFFF indicates either the fan has stalled or is running very slowly (<100 RPM).
High Limit > Comparison Performed
Figure 40. Fan with Strong TACH Pull-Up to > VCC or Totem-Pole Output, Attenuated with R1/R2
Fan Speed Measurement
The fan counter does not count the fan TACH output pulses directly, because the fan speed could be less than 1,000 RPM and it would take several seconds to accumulate a reasonably large and accurate count. Instead, the period of the fan revolution is measured by gating an on-chip 90 kHz oscillator into the input of a 16-bit counter for N periods of the fan TACH output (see Figure 41), 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 the TACH pulses per revolution register (Register 0x7B). This register contains two bits for each fan, allowing one, two (default), three, or four TACH pulses to be counted.
Because the actual fan TACH period is 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
CLOCK
PWM
TACH
1 2 3 4
04686-043
When the ADT7473 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.
Figure 41. Fan Speed Measurement
Fan Speed Measurement Registers
The fan tachometer readings are 16-bit values consisting of a 2-byte read from the ADT7473.
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
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ADT7473
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
TACH Pulses per Revolution Register
Bits [1:0] Fan 1 default = 2 pulses per revolution Bits [3:2] Fan 2 default = 2 pulses per revolution Bits [5:4] Fan 3 default = 2 pulses per revolution Bits [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
Fan Speed Measurement Rate
The fan TACH readings are normally updated once every second. The FAST bit (Bit 3) of Configuration Register 3 (0x78), when set, updates the fan TACH readings every 250 ms. If any of the fans are not being driven by a PWM channel but are powered directly from 5 V or 12 V, their associated dc bit in Configuration Register 3 should be set. This allows TACH readings to be taken on a continuous basis for fans connected directly to a dc source. For optimal results, the associated dc bit should always be set when using 4-wire fans.
Fan Spin-Up
The ADT7473 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 are detected, the PWM duty cycle goes to the expected running value, for example, 33%. The advantage is that fans have different spin-up characteristics and take different times to overcome inertia. The ADT7473 runs the fans just fast enough to overcome inertia and is quieter on spin-up than fans programmed for a given spin-up time.
Calculating Fan Speed
Assuming a fan has two pulses per revolution (and two pulses per revolution being measured), fan speed is calculated by Fan Speed (RPM) = (90,000 x 60)/Fan TACH Reading where Fan TACH Reading is the 16-bit fan tachometer reading.
Example
Fan Startup Timeout
To prevent the generation of false interrupts as a fan spins up (because it is below running speed), the ADT7473 includes a fan start-up timeout function. During this time, the ADT7473 looks for two TACH pulses. If two TACH pulses are not detected, an interrupt is generated. Using Configuration Register 1 (0x40), Bit 5 (FSPDIS), this functionality can be changed (see the Disabling Fan Startup Timeout section).
TACH1 High Byte (Register 0x29) = 0x17 TACH1 Low Byte (Register 0x28) = 0xFF What is Fan 1 speed in RPM? Fan 1 TACH Reading = 0x17FF = 6143 (decimal) RPM = (f x 60)/Fan 1 TACH Reading RPM = (90000 x 60)/6143 Fan Speed = 879 RPM
PWM1, PWM2, PWM3 Configuration Registers (Register 0x5C, Register 0x5D, and Register 0x5E)
Bits [2:0] SPIN, start-up timeout for PWM1 = 0x5C, PWM2 = 0x5D, and PWM3 = 0x5E. 000 = No start-up timeout 001 = 100 ms 010 = 250 ms default 011 = 400 ms 100 = 667 ms 101 = 1 sec 110 = 2 sec 111 = 4 sec
Fan 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 fan pulses per revolution register (Register 0x7B) for each fan. Alternatively, this register can be used to determine the number or pulses per revolution output by a given fan. By plotting fan speed measurements at a 100% speed with different pulses per revolution setting, the smoothest graph with the lowest ripple determines the correct pulses per revolution value.
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Disabling Fan Startup Timeout
Although fan start-up 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 Speed Control
The ADT7473 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 of this is that, if the system hangs, the user is guaranteed the system is protected from overheating. The automatic fan speed control incorporates a feature called dynamic TMIN calibration. This feature reduces the design effort required to program the automatic fan speed control loop. For more information and procedures on how to program the automatic fan speed control loop and dynamic TMIN calibration, see the Programming the Automatic Fan Speed Control Loop section. In manual fan speed control mode, the ADT7473 allows the duty cycle of any PWM output to be manually adjusted. This can be useful if the user wants to change fan speed in software or adjust the PWM duty cycle output for test purposes. Bits [7:5] of Register 0x5C to Register 0x5E (PWM configuration registers) control the behavior of each PWM output.
PWM Logic State
The PWM outputs can be programmed high for a 100% duty cycle (noninverted) or low for a 100% duty cycle (inverted).
PWM1 Configuration Register (0x5C)
Bit 4 INV. 0 = Logic high for a 100% PWM duty cycle 1 = Logic low for a 100% PWM duty cycle
PWM2 Configuration Register (0x5D)
Bit 4 INV. 0 = Logic high for a 100% PWM duty cycle 1 = Logic low for a 100% PWM duty cycle
PWM3 Configuration Register (0x5E)
Bit 4 INV. 0 = Logic high for a 100% PWM duty cycle 1 = Logic low for a 100% PWM duty cycle
PWM Configuration Registers (Register 0x5C to Register 0x5E)
Bits [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. In high frequency mode, the PWM drive frequency is always 22.5 kHz.
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%
High Frequency Mode PWM Drive
Setting Bit 3 of Register 0x5F enables high frequency mode for all fans.
PWM Frequency Registers (Register 0x5F to Register 0x61)
Bits [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
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)
PWM Current Duty Cycle Registers
Register 0x30, PWM1 Duty Cycle = 0x00 (0% default) Register 0x31, PWM2 Duty Cycle = 0x00 (0% default) Register 0x32, PWM3 Duty Cycle = 0x00 (0% default)
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ADT7473
By reading the PWMx current duty cycle registers, the user can keep track of the current duty cycle on each PWM output, even when the fans are running in automatic fan speed control mode or acoustic enhancement mode. See the Programming the Automatic Fan Speed Control Loop section for details.
Dynamic TMIN Control Register 1 (0X36) Bit [1] VCCPLO = 1
When the VCCP voltage drops below the VCCP low limit, the following occurs: 1. 2. 3. Status Bit 1 (VCCP) in Status Register 1 is set. SMBALERT is generated, if enabled. THERM monitoring is disabled. The THERM timer should hold its value prior to the S3 or S5 state. Dynamic TMIN control is disabled. This prevents TMIN from being adjusted due to an S3 or S5 state. The ADT7473 is prevented from entering the shutdown state.
FAN PRESENCE DETECT
This feature can be 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 steps 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 the 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.
4. 5.
Once the core voltage, VCCP, goes above the VCCP low limit, everything is re-enabled, and the system resumes normal operation.
XNOR TREE TEST MODE
The ADT7473 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. Figure 42 shows the signals that are exercised in the XNOR tree test mode. The XNOR tree test is invoked by setting Bit 0 (XEN) of the XNOR tree test enable register (0x6F).
TACH1 TACH2
As the detection time only takes 5 ms, programming the PWM outputs to 100% and then back to their normal speed is not noticeable in most cases.
Description of How Fan Presence Detect Works
Typical 4-wire fans 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, sinking 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 it is low, no fan is present. 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 (3.6 V).
TACH3
TACH4
PWM2
04686-044
SLEEP STATES
The ADT7473 has been specifically designed to operate from a 3.3 V STBY supply. In computers that support S3 and S5 states, the core voltage of the processor is lowered in these states. If using the dynamic TMIN mode, lowering the core voltage of the processor changes the CPU temperature and the dynamics of the system under dynamic TMIN control. Likewise, when monitoring THERM, the THERM timer should be disabled during these states.
PWM3 PWM1/XTO
Figure 42. XNOR Tree Test
POWER-ON DEFAULT
When the ADT7473 is powered up, it polls the VCCP input. If VCCP stays below 0.75 V (the system CPU power rail is not powered up), the ADT7473 assumes the functionality of the default registers after the ADT7473 is addressed via any valid SMBus transaction.
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ADT7473
If VCC goes high (the system processor power rail is powered up), a fail-safe timer begins to count down. If the ADT7473 is not addressed by any valid SMBus transactions before the failsafe timeout (4.6 seconds) lapses, the ADT7473 drives the fans to full speed. If the ADT7473 is addressed by a valid SMBus transaction after this point, the fans stop, and the ADT7473 assumes its default settings and begins normal operation. If VCCP goes high (the system processor power rail is powered up), then a fail-safe timer begins to count down. If the ADT7473 is addressed by a valid SMBus transaction before the fail-safe timeout (4.6 seconds) lapses, then the ADT7473 operates normally, assuming the functionality of all the default registers. See the flow chart in Figure 43.
ADT7473 IS POWERED UP
Y
HAS THE ADT7473 BEEN ACCESSED BY A VALID SMBus TRANSACTION? N IS VCCP ABOVE 0.75V? Y START FAIL-SAFE TIMER CHECK VCCP
N
Y
HAS THE ADT7473 BEEN ACCESSED BY A VALID SMBus TRANSACTION? N FAIL-SAFE TIMER ELAPSES AFTER THE FAIL-SAFE TIMEOUT
HAS THE ADT7473 BEEN ACCESSED BY A VALID SMBus TRANSACTION? Y
N
RUNS THE FANS TO FULL SPEED
HAS THE ADT7473 BEEN ACCESSED BY A VALID SMBus TRANSACTION? Y START UP THE ADT7473 NORMALLY SWITCH OFF FANS
N
Figure 43. Power-On Flow Chart
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ADT7473 PROGRAMMING THE AUTOMATIC FAN SPEED CONTROL LOOP
To understand the automatic fan speed control loop, it is strongly recommended to use the ADT7473 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 consider the system configuration, including the number of fans, where they are located, and what temperatures are measured in the particular system. The mechanical or thermal engineer who is tasked with the system thermal characterization should also be involved at the beginning of the process. 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 44 gives a top-level overview of the automatic fan control circuitry on the ADT7473. 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 ADT7473 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, a designer 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 44 shows controls that are fan-specific. The designer has individual control over parameters such as minimum PWM duty cycle, fan speed failure thresholds, and even ramp control of the PWM outputs. Automatic fan control, then, ultimately allows graceful fan speed changes that are less perceptible to the system user.
AUTOMATIC FAN CONTROL OVERVIEW
The ADT7473 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. The ADT7473 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 CPUs and other CPUs). These three temperature channels can be used as the basis for automatic fan speed control to drive fans using PWM.
THERMAL CALIBRATION
100%
PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT)
PWM CONFIG PWM GENERATOR
PWM1
REMOTE 1 TEMP
TMIN
TRANGE
0% PWM MIN
THERMAL CALIBRATION
TACHOMETER 1 MEASUREMENT
100%
PWM CONFIG PWM GENERATOR
TACH1
MUX
0% PWM MIN
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 2 MEASUREMENT
PWM2
LOCAL TEMP
TMIN
TRANGE
THERMAL CALIBRATION
PWM CONFIG PWM GENERATOR
TACH2
100%
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 3 AND 4 MEASUREMENT
PWM3
REMOTE 2 TEMP
TMIN
TRANGE
Figure 44. Automatic Fan Control Block Diagram
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0%
TACH3
ADT7473
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. Consider the following questions: 1. What ADT7473 functionality will be used? * * PWM2 or SMBALERT? TACH4 fan speed measurement or overtemperature THERM function? 4. 2. How many fans will be supported in the 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 ADT7473 or will it run at full speed 100% of the time? If run at full speed, 100% of the time, this frees up a PWM output, but the system is louder. Where will the ADT7473 be physically located in the system? This influences the assignment of the temperature measurement channels to particular system thermal zones. For example, locating the ADT7473 close to the VRM controller circuitry allows the VRM temperature to be monitored using the local temperature channel.
3.
The ADT7473 offers multifunctional pins that can be reconfigured to suit different system requirements and physical layouts. These multifunction pins are software programmable.
THERMAL CALIBRATION
100%
PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT)
PWM CONFIG PWM GENERATOR
PWM1
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0% PWM MIN
THERMAL CALIBRATION
TACHOMETER 1 MEASUREMENT
100%
PWM CONFIG PWM GENERATOR
TACH1 CPU FAN SINK
MUX
0% PWM MIN
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 2 MEASUREMENT
PWM2
TMIN LOCAL = VRM TEMP
TRANGE
THERMAL CALIBRATION
PWM CONFIG PWM GENERATOR
TACH2
100%
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 3 AND 4 MEASUREMENT
FRONT CHASSIS PWM3
TMIN REMOTE 2 = CPU TEMP
TRANGE
0%
TACH3
REAR CHASSIS
Figure 45. Hardware Configuration Example
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ADT7473
Recommended Implementation 1
Configuring the ADT7473, as in Figure 46, provides the system designer with 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 core voltage measurement (VCORE). VRM temperature using local temperature sensor. * * * * CPU temperature measured using the Remote 1 temperature channel. Ambient temperature measured through the Remote 2 temperature channel. Bidirectional THERM pin allows the monitoring of PROCHOT output from an Intel Pentium 4 processor, for example, or can be used as an overtemperature THERM output. SMBALERT system interrupt output.
FRONT CHASSIS FAN
ADT7473
TACH2 PWM1 TACH1 CPU FAN
REAR CHASSIS FAN
PWM3 TACH3 D2+ D2- THERM PROCHOT CPU
AMBIENT TEMPERATURE
D1+ D1- SDA SCL SMBALERT ICH
Figure 46. Recommended Implementation 1
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GND
ADT7473
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.
Automatic Fan Control Mux Options
Bits [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 101 = Fastest speed calculated by local and Remote 2 temperature controls PWMx 110 = Fastest speed calculated by all three temperature channel 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 is the fan turning on when Remote 1 temperature exceeds 60C, or if the local temperature exceeds 45C.
Other Mux Options
Bits [7:5] (BHVR), Register 0x5C, Register 0x5D, Register 0x5E. 011 = PWMx runs full speed 100 = PWMx disabled (default) 111 = manual mode In normal mode, PWMx runs under software control. In this mode, PWM duty cycle registers (Register 0x30 to Register 0x32) are writable and control the PWM outputs.
MUX
THERMAL CALIBRATION
100%
PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT)
PWM CONFIG PWM GENERATOR
PWM1
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0% PWM MIN
THERMAL CALIBRATION
TACHOMETER 1 MEASUREMENT
100%
PWM CONFIG PWM GENERATOR
TACH1 CPU FAN SINK
MUX
0% PWM MIN
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 2 MEASUREMENT
PWM2
TMIN LOCAL = VRM TEMP
TRANGE
THERMAL CALIBRATION
PWM CONFIG PWM GENERATOR
TACH2
100%
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 3 AND 4 MEASUREMENT
FRONT CHASSIS PWM3
TMIN REMOTE 2 = CPU TEMP
TRANGE
0%
TACH3
REAR CHASSIS
Figure 47. Assigning Temperature Channels to Fan Channels
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ADT7473
Mux Configuration Example
This is an example of how to configure the mux in a system using the ADT7473 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 behaviors: * 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 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
Bits [7:5] (BHVR), PWM1 Configuration Register (0x5C) 101 = Fastest speed calculated by local and Remote 2 temperature controls PWM1 Bits [7:5] (BHVR), PWM2 Configuration Register (0x5D) 000 = Remote 1 temperature controls PWM2 Bits [7:5] (BHVR), PWM3 Configuration Register (0x5E) 000 = Remote 1 temperature controls PWM3 These settings configure the mux, as shown in Figure 48.
* *
THERMAL CALIBRATION
100%
PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT)
PWM CONFIG PWM GENERATOR
PWM1
TMIN REMOTE 2 = CPU TEMP
TRANGE
0%
THERMAL CALIBRATION
MUX
100%
PWM MIN
TACHOMETER 1 MEASUREMENT
PWM CONFIG PWM GENERATOR
TACH1 CPU FAN SINK
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TMIN TRANGE 0% PWM MIN TACHOMETER 2 MEASUREMENT
PWM2
LOCAL = VRM TEMP
THERMAL CALIBRATION
PWM CONFIG PWM GENERATOR
TACH2
100%
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 3 AND 4 MEASUREMENT
FRONT CHASSIS PWM3
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0%
TACH3
REAR CHASSIS
Figure 48. Mux Configuration Example
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ADT7473
STEP 3: TMIN SETTINGS FOR THERMAL CALIBRATION CHANNELS
TMIN is the temperature at which the fans start to turn on under automatic fan control. The speed at which the fan runs at TMIN is programmed later. The TMIN values chosen are temperature channel specific, for example, 25C for ambient channel, 30C for VRM temperature, and 40C for processor temperature. TMIN is an 8-bit value, either twos complement or Offset 64, that can be programmed in 1C increments. 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 drops below TMIN - THYST. To overcome fan inertia, the fan is spun up until two valid TACH rising edges are counted. (See the Fan Startup Timeout section for more details.) In some cases, primarily for psychoacoustic reasons, it is desirable that the fan never switches off below TMIN. Bits [7:5] of Enhance Acoustics Register 1 (0x62), when set, can keep the fans running at the PWM minimum duty cycle, if the temperature falls below TMIN.
TMIN Registers
Register 0x67, Remote 1 Temperature TMIN = 0x9A (90C) Register 0x68, Local Temperature TMIN = 0x9A (90C) Register 0x69, Remote 2 Temperature TMIN = 0x9A (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.
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ADT7473
100%
PWM DUTY CYCLE
0% TMIN
THERMAL CALIBRATION
100%
PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT)
PWM CONFIG PWM GENERATOR
PWM1
TMIN REMOTE 2 = CPU TEMP
TRANGE
0% PWM MIN
THERMAL CALIBRATION
TACHOMETER 1 MEASUREMENT
100%
PWM CONFIG PWM GENERATOR
TACH1 CPU FAN SINK
MUX
0% PWM MIN
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 2 MEASUREMENT
PWM2
TMIN LOCAL = VRM TEMP
TRANGE
THERMAL CALIBRATION
PWM CONFIG PWM GENERATOR
TACH2
100%
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 3 AND 4 MEASUREMENT
FRONT CHASSIS PWM3
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0%
TACH3
REAR CHASSIS
Figure 49. Understanding the TMIN Parameter
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ADT7473
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 (see Figure 50). For maximum system acoustic benefit, PWMMIN should be set 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%
Programming the PWMMIN Registers
The PWMMIN registers are 8-bit registers that allow the minimum PWM duty cycle for each output to be configured anywhere from 0% to 100%. This allows the minimum PWM duty cycle to be set in steps of 0.39%. The value to be programmed into the PWMMIN register is given by Value (decimal) = PWMMIN/0.39
Example 1: For a minimum PWM duty cycle of 50%
PWM DUTY CYCLE
Value (decimal) = 50/0.39 = 128 (decimal) Value = 128 (decimal) or 80 (hex)
Example 2: For a minimum PWM duty cycle of 33%
PWMMIN 0% TEMPERATURE
04686-052
Value (decimal) = 33/0.39 = 85 (decimal) Value = 85 (decimal) or 54 (hex)
PWMMIN Registers
Register 0x64, PWM1 Minimum Duty Cycle = 0x80 (50% default) Register 0x65, PWM2 Minimum Duty Cycle = 0x80 (50% default) Register 0x66, PWM3 Minimum Duty Cycle = 0x80 (50% default)
TMIN
Figure 50. 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 51 illustrates this as PWM1MIN (front fan) is turned on at a minimum duty cycle of 20%, while PWM2MIN (rear fan) turns on at a minimum of 40% duty cycle. However, both fans turn on at exactly the same temperature, defined by TMIN.
100%
Note on Fan Speed and PWM Duty Cycle
The PWM duty cycle does not directly correlate to fan speed in RPM. Running a fan at 33% PWM duty cycle does not equate to running the fan at 33% speed. Driving a fan at 33% PWM duty cycle actually runs the fan at closer to 50% of its full speed. This is because fan speed in %RPM generally relates to the square root of PWM duty cycle. Given a PWM square wave as the drive signal, fan speed in RPM approximates to
% fanspeed = PWM duty cycle x 10
PWM DUTY CYCLE
M2 PW M1 PW
PWM2MIN PWM1MIN 0%
STEP 5: PWMMAX FOR PWM (FAN) OUTPUTS
PWMMAX is the maximum duty cycle at which each fan in the system runs 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 (see Figure 52). There is a PWMMAX limit for each fan channel. The default value of this register is 0xFF and thus has no effect unless it is programmed.
TMIN
TEMPERATURE
Figure 51. Operating Two Different Fans from a Single Temperature Channel
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ADT7473
100%
PWM DUTY CYCLE
STEP 6: TRANGE FOR TEMPERATURE CHANNELS
TRANGE is the range of temperature over which automatic fan control occurs once the programmed TMIN temperature is exceeded. TRANGE is a temperature slope, not an arbitrary value, that is, a TRANGE of 40C holds true only for PWMMIN = 33%. If PWMMIN is increased or decreased, the effective TRANGE changes. Refer to Figure 53.
TRANGE
04686-054
PWMMAX
PWMMIN 0% TMIN TEMPERATURE
100%
Programming the PWMMAX Registers
The PWMMAX registers are 8-bit registers that allow the maximum PWM duty cycle for each output to be configured anywhere from 0% to 100%. This allows the maximum PWM duty cycle to be set in steps of 0.39%. The value to be programmed into the PWMMAX register is given by Value (decimal) = PWMMAX/0.39
Example 1: For a maximum PWM duty cycle of 50%
PWM DUTY CYCLE
Figure 52. PWMMAX Determines Maximum PWM Duty Cycle Below the THERM Temperature Limit
PWMMIN 0% TMIN TEMPERATURE
04686-055 04686-056
Figure 53. TRANGE Parameter Affects Cooling Slope
The TRANGE or fan control slope is determined by the following procedure: 1. 2. Determine the maximum operating temperature for that channel (for example, 70C). Determine experimentally the fan speed (PWM duty cycle value) that does not exceed the temperature at the worstcase operating points (for example, 70C is reached when the fans are running at 50% PWM duty cycle). Determine the slope of the required control loop to meet these requirements. Graphically program and visualize this functionality using the ADT7473 evaluation software. Ask your local Analog Devices representative for details.
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)
3. 4.
PWMMAX 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) See the Note on Fan Speed and PWM Duty Cycle section.
Figure 54 shows how adjusting PWMMIN affects TRANGE.
100%
PWM DUTY CYCLE
50% 33% 0% 30C 40C TMIN
Figure 54. Adjusting PWMMIN Affects TRANGE
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ADT7473
TRANGE is implemented as a slope, which means that as PWMMIN is changed, TRANGE changes, but the actual slope remains the same. The higher the PWMMIN value, the smaller the effective TRANGE, that is, the fan reaches full speed (100%) at a lower temperature. Figure 55 shows how increasing PWMMIN changes the effective TRANGE.
Example 3: Calculate TMAX, given that TMIN = 30C, TRANGE = 40C, and PWMMIN = 33% duty cycle = 85 (decimal).
TMAX = TMIN + (Max DC - Min DC) x TRANGE /170 TMAX = 30C + (100% - 33%) x 40C/170 TMAX = 30C + (255 - 85) x 40C/170 TMAX = 70C (effective TRANGE = 40C)
Example 4: Calculate TMAX, given that TMIN = 30C, TRANGE = 40C, and PWMMIN = 50% duty cycle = 128 (decimal).
100%
PWM DUTY CYCLE
50% 33% 25% 10% 0% 30C 40C
04686-057
TMAX = TMIN + (Max DC - Min DC) x TRANGE /170 TMAX = 30C + (100% - 50%) x 40C/170 TMAX = 30C + (255 - 128) x 40C/170 TMAX = 60C (effective TRANGE = 30C)
Selecting a TRANGE Slope
The TRANGE value can be selected for each temperature channel: Remote 1, local, and Remote 2. Bits [7:4] (TRANGE) of Register 0x5F to Register 0x61 define the TRANGE value for each temperature channel.
Table 14. 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
45C 54C TMIN
Figure 55. Increasing PWMMIN Changes Effective TRANGE
For a given TRANGE value, the temperature at which the fan runs at full speed for different PWMMIN values can be easily calculated as follows: TMAX = TMIN + (Max DC - Min DC) x TRANGE /170 where: TMAX is the temperature at which the fan runs full speed. TMIN is the temperature at which the fan turns on. Max DC is the maximum duty cycle (100%) = 255 decimal. Min DC is equal to PWMMIN. TRANGE is the duty PWM duty cycle vs. temperature slope.
Example 1: Calculate T, given that TMIN = 30C, TRANGE = 40C, and PWMMIN = 10% duty cycle = 26 (decimal).
TRANGE (C) 2 2.5 3.33 4 5 6.67 8 10 13.33 16 20 26.67 32 (default) 40 53.33 80
TMAX = TMIN + (Max DC - Min DC) x TRANGE /170 TMAX = 30C + (100% - 10%) x 40C/170 TMAX = 30C + (255 - 26) x 40C/170 TMAX = 84C (effective TRANGE = 54C)
Example 2: Calculate TMAX, given that TMIN = 30C, TRANGE = 40C, and PWMMIN = 25% duty cycle = 64 (decimal).
Register 0x5F configures Remote 1 TRANGE; Register 0x60 configures local TRANGE; Register 0x61 configures Remote 2 TRANGE.
Summary of TRANGE Function
When using the automatic fan control function, the temperature at which the fan reaches full speed can be calculated by TMAX = TMIN + TRANGE Equation 1 holds true only when PWMMIN is equal to 33% PWM duty cycle. (1)
TMAX = TMIN + (Max DC - Min DC) x TRANGE /170 TMAX = 30C + (100% - 25%) x 40C/170 TMAX = 30C + (255 - 64) x 40C/170 TMAX = 75C (effective TRANGE = 45C)
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ADT7473
Increasing or decreasing PWMMIN changes the effective TRANGE, although the fan control still follows the same PWM duty cycle to temperature slope. The effective TRANGE for different PWMMIN values can be calculated using Equation 2. TMAX = TMIN + (Max DC - Min DC) x TRANGE/170 (2) The graphs in Figure 56 assume 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 57 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.
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
where (Max DC - Min DC) x TRANGE/170 is the effective TRANGE value. See the Note on Fan Speed and PWM Duty Cycle section.
PWM DUTY CYCLE (%)
70 60 50 40 30 20 10 0 0
Figure 56 shows PWM duty cycle vs. temperature for each TRANGE setting. The lower graph shows how each TRANGE setting affects fan speed vs. temperature. As indicated by the graph, the effect on fan speed is nonlinear.
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
PWM DUTY CYCLE (%)
70 60 50 40 30 20 10 0 0
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
04686-059
FAN SPEED (% OF MAX)
70 60 50 40 30 20 10 0 0
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
04686-058
FAN SPEED (% OF MAX)
70 60 50 40 30 20 10 0 0
Figure 57. TRANGE and % Fan Speed Slopes with PWMMIN = 20%
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 = 53.3C for CPU temperature TRANGE = 40C for VRM temperature This example uses the mux configuration described in the Step 2: Configuring the Mux section, with the ADT7473 connected as shown in Figure 58. 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 torun at PWMMIN = 30%. The CPU fan is configured to run at PWMMIN = 10%.
Figure 56. TRANGE vs. Actual Fan Speed Profile
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ADT7473
Note on 4-Wire Fans
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%.
100 90 80
PWM DUTY CYCLE (%)
The fans remain running at 100% until the temperature drops below TTHERM - hysteresis, where hysteresis is the number programmed into the hysteresis registers (Register 0x6D and Register 0x6E). The default hysteresis value is 4C. The TTHERM limit should be considered the maximum worst-case operating temperature of the system. Because exceeding any TTHERM limit runs all fans at 100%, it has very negative acoustic effects. Ultimately, this limit should be set up as a fail-safe, and one should ensure it is not exceeded under normal system operating conditions. Note that the TTHERM limits are nonmaskable and affect the fan speed no matter how the 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).
70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100
TEMPERATURE ABOVE TMIN 100 90 80
FAN SPEED (% MAX RPM)
THERM Registers
Register 0x6A, Remote 1 THERM Temperature Limit = 0xA4 (100C default) Register 0x6B, Local THERM Temperature Limit = 0xA4 (100C default) Register 0x6C, Remote 2 THERM Temperature Limit = 0xA4 (100C default)
70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100
04686-060
Hysteresis Registers
Register 0x6D, Remote 1 Local Temperature Hysteresis Register Bits [7:4] Remote 1 temperature hysteresis (4C default) Bits [3:0] Local temperature hysteresis (4C default) Register 0x6E, Remote 2 Temperature Hysteresis Register Bits [7:4] Remote 2 temperature hysteresis (4C default) Because each hysteresis setting is four bits, hysteresis values are programmable from 1C to 15C. It is not recommended that hysteresis values be programmed to 0C, because this disables hysteresis. In effect, this would cause the fans to cycle between normal speed and 100% speed, creating unsettling acoustic noise.
TEMPERATURE ABOVE TMIN
Figure 58. TRANGE and % Fan Speed Slopes for VRM, Ambient, and CPU Temperature Channels
STEP 7: TTHERM FOR TEMPERATURE CHANNELS
TTHERM is the absolute maximum temperature allowed on a temperature channel. When operating above this temperature, a component such as the CPU or VRM might be 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.
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ADT7473
TRANGE 100%
PWM DUTY CYCLE
0% TMIN TTHERM
THERMAL CALIBRATION
100%
PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT)
PWM CONFIG PWM GENERATOR
PWM1
TMIN REMOTE 2 = CPU TEMP
TRANGE
0% PWM MIN
THERMAL CALIBRATION
TACHOMETER 1 MEASUREMENT
100%
PWM CONFIG PWM GENERATOR
TACH1 CPU FAN SINK
MUX
0% PWM MIN
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 2 MEASUREMENT
PWM2
TMIN LOCAL = VRM TEMP
TRANGE
THERMAL CALIBRATION
PWM CONFIG PWM GENERATOR
TACH2
100%
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 3 AND 4 MEASUREMENT
FRONT CHASSIS PWM3
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0%
TACH3
REAR CHASSIS
Figure 59. How TTHERM Relates to Automatic Fan Control
STEP 8: THYST FOR TEMPERATURE CHANNELS
THYST is the amount of extra cooling a fan provides after the temperature measured has dropped back below TMIN before the fan turns off. The premise for temperature hysteresis (THYST) is that, without it, the fan would merely chatter or cycle on and off regularly whenever temperature is hovering at about the TMIN setting. The THYST value chosen determines the amount of time needed for the system to cool down or heat up as the fan turns 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.
Hysteresis Registers
Register 0x6D, Remote 1, Local Hysteresis Register Bits [7:4] Remote 1 temperature hysteresis (4C default) Bits [3:0] Local temperature hysteresis (4C default) Register 0x6E, Remote 2 Temperature Hysteresis Register Bits [7:4], Remote 2 temperature hysteresis (4C default) In some applications, it is required that fans not turn off below TMIN, but remain running at PWMMIN. Bits [7:5] of the 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.
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ADT7473
TRANGE 100%
PWM DUTYCYCLE
0% TMIN TTHERM
THERMAL CALIBRATION
100%
PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT)
PWM CONFIG PWM GENERATOR
PWM1
TMIN REMOTE 2 = CPU TEMP
TRANGE
0% PWM MIN
THERMAL CALIBRATION
TACHOMETER 1 MEASUREMENT
100%
PWM CONFIG PWM GENERATOR
TACH1 CPU FAN SINK
MUX
0% PWM MIN
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 2 MEASUREMENT
PWM2
TMIN LOCAL = VRM TEMP
TRANGE
THERMAL CALIBRATION
PWM CONFIG PWM GENERATOR
TACH2
100%
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 3 AND 4 MEASUREMENT
FRONT CHASSIS PWM3
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0%
TACH3
REAR CHASSIS
Figure 60. The THYST Value Applies to Fan On/Off Hysteresis and THERM Hysteresis
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.
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ADT7473
DYNAMIC TMIN CONTROL MODE
In addition to the automatic fan speed control mode described in the Automatic Fan Control Overview section, the ADT7473 has a mode that extends the basic automatic fan speed control loop. Dynamic TMIN control allows the ADT7473 to intelligently adapt the system's cooling solution for best system performance or lowest possible system acoustics, depending on user or design requirements. Use of dynamic TMIN control alleviates the need to design for worst-case conditions and significantly reduces system design and validation time.
VENTS FAN I/O CARDS I/O CARDS POWER SUPPLY VENTS POWER SUPPLY FAN
GOOD CPU AIRFLOW
CPU
POOR CPU AIRFLOW
CPU
FAN VENTS
DRIVE BAYS
DRIVE BAYS
04686-063
GOOD VENTING = GOOD AIR EXCHANGE
POOR VENTING = POOR AIR EXCHANGE
Designing for Worst-Case Conditions
System design must always allow for worst-case conditions. In PC design, the worst-case conditions include, but are not limited to the following:
Worst-Case Altitude
Figure 61. Chassis Airflow Issues
Worst-Case Processor Power Consumption
A computer can be operated at different altitudes. The altitude affects the relative air density, which alters the effectiveness of the fan cooling solution. For example, comparing 40C air temperature at 10,000 feet to 20C air temperature at sea level, relative air density is increased by 40%. This means that the fan can spin 40% slower and make less noise at sea level than at 10,000 feet while keeping the system at the same temperature at both locations.
Worst-Case Fan
This data sheet maximum does not necessarily reflect the true processor power consumption. Designing for worst-case CPU power consumption can result in a processor becoming overcooled (generating excess system noise).
Worst-Case Peripheral Power Consumption
The tendency is to design to data sheet maximums for peripheral components, again overcooling the system.
Worst-Case Assembly
Due to manufacturing tolerances, fan speeds in RPM are normally quoted with a tolerance of 20%. The designer needs to assume that the fan RPM can be 20% below tolerance. This translates to reduced system airflow and elevated system temperature. Note that fans 20% out of tolerance can negatively impact system acoustics because they run faster and generate more noise.
Worst-Case Chassis Airflow
Every system is unique because of manufacturing variations. Heat sinks may be loose fitting or slightly misaligned. Too much or too little thermal grease might be used, or variations in application pressure for thermal interface material could affect the efficiency of the thermal solution. Accounting for manufacturing variations in every system is difficult; therefore, the system must be designed for the worst case.
TA HEAT SINK THERMAL INTERFACE MATERIAL INTEGRATED HEAT SPREADER
SA TIMS CTIM TIMC
TS TTIM TC
CS
CA
JA
The same motherboard can be used in a number of different chassis configurations. The design of the chassis and the physical location of fans and components determine the system thermal characteristics. Moreover, for a given chassis, the addition of add-in cards, cables, or other system configuration options can alter the system airflow and reduce the effectiveness of the system cooling solution. The cooling solution can also be inadvertently altered by the end user. (For example, placing a computer against a wall can block the air ducts and reduce system airflow.)
JTIM SUBSTRATE EPOXY THERMAL INTERFACE MATERIAL
PROCESSOR
TTIM
04686-064
TJ
Figure 62. Thermal Model
Although a design usually accounts for worst-case conditions in all these cases, the actual system is almost never operated at worst-case conditions. The alternative to designing for the worst case is to use the dynamic TMIN control function.
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ADT7473
Dynamic TMIN Control Overview
Dynamic TMIN control mode builds upon the basic automatic fan control loop by adjusting the TMIN value based on system performance and measured temperature. This is important because instead of designing for the worst case, the system thermals can be defined as operating zones. The ADT7473 can self-adjust its fan control loop to maintain either an operating zone temperature or a system target temperature. For example, it can be specified that the ambient temperature in a system should be maintained at 50C. If the temperature is below 50C, the fans might not need to run, or might run very slowly. If the temperature is higher than 50C, the fans need to throttle up. The challenge presented by any thermal design is finding the right settings to suit the system's fan control solution. This can involve designing for the worst case, followed by weeks of system thermal characterization, and finally fan acoustic optimization (for psycho-acoustic reasons). Getting the most benefit from the automatic fan control mode involves characterizing the system to find the best TMIN and TRANGE settings for the control loop, and the best PWMMIN value for the quietest fan speed setting. Using the ADT7473's dynamic TMIN control mode, however, shortens the characterization time and alleviates tweaking the control loop settings because the device can self-adjust during system operation. Dynamic TMIN control mode is operated by specifying the operating zone temperatures required for the system. Associated with this control mode are three operating point registers, one for each temperature channel. This allows the system thermal solution to be broken down into distinct thermal zones. For example, CPU operating temperature is 70C, VRM operating temperature is 80C, and ambient operating temperature is 50C. The ADT7473 dynamically alters the control solution to maintain each zone temperature as closely as possible to its target operating point. Figure 63 shows an overview of the parameters that affect the operation of the dynamic TMIN control loop.
PWM DUTY CYCLE
TEMPERATURE TLOW TMIN OPERATING THIGH TTHERM TRANGE POINT
04686-065
Figure 63. Dynamic TMIN Control Loop
Table 15 provides a brief description of each parameter.
Table 15. TMIN Control Loop Parameters
Parameter TLOW Description If the temperature drops below the TLOW limit, an error flag is set in a status register and an SMBALERT interrupt can be generated. If the temperature exceeds the THIGH limit, an error flag is set in a status register and an SMBALERT interrupt can be generated. The temperature at which the fan turns on under automatic fan speed control. The target temperature for a particular temperature zone. The ADT7473 attempts to maintain system temperature at about the operating point by adjusting the TMIN parameter of the control loop. If the temperature exceeds this critical limit, the fans can be run at 100% for maximum cooling. Programs the PWM duty cycle vs. temperature control slope.
THIGH
TMIN Operating Point
TTHERM TRANGE
Dynamic TMIN Control Programming
Because the dynamic TMIN control mode is a basic extension of the automatic fan control mode, program the automatic fan control mode parameters first, as described in Step 1: Hardware Configuration to Step 8: THYST for Temperature Channels, then proceed with dynamic TMIN control mode programming.
Operating Point Registers
Register 0x33, Remote 1 Operating Point = 0xA4 (100C default) Register 0x34, Local Temperature Operating Point = 0xA4 (100C default) Register 0x35, Remote 2 Operating Point = 0xA4 (100C default)
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ADT7473
STEP 9: OPERATING POINTS FOR TEMPERATURE CHANNELS
The operating point for each temperature channel is the optimal temperature for that thermal zone. The hotter each zone is allowed to be, the quieter the system, because the fans are not required to run as fast. The ADT7473 increases or decreases fan speeds as necessary to maintain the operating point temperature, allowing for system-to-system variation and removing the need for worst-case design. If a sensible operating point value is chosen, any TMIN value can be selected in the system characterization. If the TMIN value is too low, the fans run sooner than required, and the temperature is below the operating point. In response, the ADT7473 increases TMIN to keep the fans off longer and to allow the temperature zone to get closer to the operating point. Likewise, too high a TMIN value causes the operating point to be exceeded, and in turn, the ADT7473 reduces TMIN to turn the fans on sooner to cool the system.
Programming Operating Point Registers
There are three operating point registers, one for each temperature channel. These 8-bit registers allow the operating point temperatures to be programmed with 1C resolution.
Operating Point Registers
Register 0x33, Remote 1 Operating Point = 0xA4 (100C default) Register 0x34, Local Operating Point = 0xA4 (100C default) Register 0x35, Remote 2 Operating Point = 0xA4 (100C default)
THERMAL CALIBRATION
100% OPERATING POINT
PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 1 MEASUREMENT
PWM CONFIG PWM GENERATOR
PWM1
TMIN REMOTE 2 = CPU TEMP
TRANGE
0% PWM MIN
THERMAL CALIBRATION
100%
PWM CONFIG PWM GENERATOR
TACH1 CPU FAN SINK
MUX
0% PWM MIN
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 2 MEASUREMENT
PWM2
TMIN LOCAL = VRM TEMP
TRANGE
THERMAL CALIBRATION
PWM CONFIG PWM GENERATOR
TACH2
100%
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 3 AND 4 MEASUREMENT
FRONT CHASSIS PWM3
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0%
TACH3
REAR CHASSIS
Figure 64. Operating Point Value Dynamically Adjusts Automatic Fan Control Settings
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ADT7473
STEP 10: HIGH AND LOW LIMITS FOR TEMPERATURE CHANNELS
The low limit defines the temperature at which the TMIN value starts to be increased, if temperature falls below this value. This has the net effect of reducing the fan speed, allowing the system to get hotter. An interrupt can be generated when the temperature drops below the low limit. The high limit defines the temperature at which the TMIN value starts to be reduced, if temperature increases above this value. This has the net effect of increasing fan speed to cool down the system. An interrupt can be generated when the temperature rises above the high limit.
Short Cycle and Long Cycle
The ADT7473 implements two loops: a short cycle and a long cycle. The short cycle takes place every n monitoring cycles. The long cycle takes place every 2n monitoring cycles. The value of n is programmable for each temperature channel. The bits are located at the following register locations: Remote 1 = CYR1 = Bits [2:0] of Dynamic TMIN Control Register 2 (0x37). Local = CYL = Bits [5:3] of Dynamic TMIN Control Register 2 (0x37). Remote 2 = CYR2 = Bits [7:6] of Dynamic TMIN Control Register 2 (0x37) and Bit 0 of Dynamic TMIN Control Register 1 (0x36).
Table 16. Cycle Bit Assignments
Code 000 001 010 011 100 101 110 111 Short Cycle 8 cycles 16 cycles 32 cycles 64 cycles 128 cycles 256 cycles 512 cycles 1024 cycles 1 sec 2 sec 4 sec 8 sec 16 sec 32 sec 64 sec 128 sec Long Cycle 16 cycles 32 cycles 64 cycles 128 cycles 256 cycles 512 cycles 1024 cycles 2048 cycles 2 sec 4 sec 8 sec 16 sec 32 sec 64 sec 128 sec 256 sec
Programming High and Low Limits
There are six limit registers; a high limit and low limit are associated with each temperature channel. These 8-bit registers allow the high and low limit temperatures to be programmed with 1C resolution.
Temperature Limit Registers
Register 0x4E, Remote 1 Temperature Low Limit = 0x01 Register 0x4F, Remote 1 Temperature High Limit = 0x7F Register 0x50, Local Temperature Low Limit = 0x01 Register 0x51, Local Temperature High Limit = 0x7F Register 0x52, Remote 2 Temperature Low Limit = 0x01 Register 0x53, Remote 2 Temperature High Limit = 0x7F
How Dynamic TMIN Control Works
The basic premise is as follows: 1. Set the target temperature for the temperature zone, which could be, for example, the Remote 1 thermal diode. This value is programmed to the Remote 1 operating temperature register. As the temperature in that zone (Remote 1 temperature) rises toward and exceeds the operating point temperature, TMIN is reduced, and the fan speed increases. As the temperature drops below the operating point temperature, TMIN is increased, and the fan speed is reduced.
Care should be taken when choosing the cycle time. A long cycle time means that TMIN is updated less often. If your system has very fast temperature transients, the dynamic TMIN control loop is always lagging. If a cycle time is chosen that is too fast, the full benefit of changing TMIN might not be realized and needs to change again on the next cycle; in effect, it is overshooting. It is necessary to carry out some calibration to identify the most suitable response time. Figure 65 shows the steps taken during the short cycle.
WAIT n MONITORING CYCLES CURRENT TEMPERATURE MEASUREMENT T1(n) OPERATING POINT TEMPERATURE OP1 PREVIOUS TEMPERATURE MEASUREMENT T1 (n - 1)
2.
IS T1(n) > (OP1 - HYS) YES
NO
DO NOTHING
3.
IS T1(n) - T1(n - 1) 0.25C NO
YES
DO NOTHING (SYSTEM IS COOLING OFF FOR CONSTANT)
However, the loop operation is not as simple as described in these steps. A number of conditions govern the situations in which TMIN can increase or decrease.
IS T1(n) - T1(n - 1) > 2.0C
Figure 65. Short Cycle Steps
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04686-067
IS T1(n) - T1(n - 1) = 0.5 - 0.75C IS T1(n) - T1(n - 1) = 1.0 - 1.75C
DECREASE T MIN BY 1C DECREASE T MIN BY 2C DECREASE T MIN BY 4C
ADT7473
Figure 66 shows the steps taken during the long cycle.
WAIT 2n MONITORING CYCLES CURRENT TEMPERATURE MEASUREMENT T1(n) OPERATING POINT TEMPERATURE OP1
IS T1(n) > OP1
YES
DECREASE TMIN BY 1C
NO IS T1(n) < LOW TEMP LIMIT AND TMIN < HIGH TEMP LIMIT YES AND TMIN < OP1 AND T1(n) > TMIN NO
Once the temperature exceeds the operating temperature minus the hysteresis (OP - Hyst), TMIN starts to decrease. This occurs during the short cycle (see Figure 65). The rate at which TMIN decreases depends on the programmed value of n. It also depends on how much the temperature has increased between this monitoring cycle and the last monitoring cycle, that is, if the temperature has increased by 1C, then TMIN is reduced by 2C. Decreasing TMIN has the effect of increasing the fan speed, thus providing more cooling to the system. If the temperature slowly increases only in the range (OP - Hyst), that is, 0.25C per short monitoring cycle, then TMIN does not decrease. This allows small changes in temperature in the desired operating zone without changing TMIN. The long cycle makes no change to TMIN in the temperature range (OP - Hyst) because the temperature has not exceeded the operating temperature. Once the temperature exceeds the operating temperature, the long cycle causes TMIN to be reduced by 1C every long cycle while the temperature remains above the operating temperature. This takes place in addition to the decrease in TMIN that occurs due to the short cycle. In Figure 68, because the temperature is increasing at a rate 0.25C per short cycle, no reduction in TMIN takes place during the short cycle. Once the temperature falls below the operating temperature, TMIN stays the same. Even when the temperature starts to increase slowly, TMIN stays the same because the temperature increases at a rate 0.25C per cycle.
Example 3: Increase TMIN Cycle
INCREASE TMIN BY 1C
Figure 66. Long Cycle Steps
The following examples illustrate some of the circumstances that might cause TMIN to increase, decrease, or stay the same.
Example 1: Normal Operation--No TMIN Adjustment
*
If measured temperature never exceeds the programmed operating point minus the hysteresis temperature, then TMIN is not adjusted, that is, it remains at its current setting. If measured temperature never drops below the low temperature limit, then TMIN is not adjusted.
THERM LIMIT HIGH TEMP LIMIT OPERATING POINT
*
04686-068
DO NOT CHANGE
HYSTERESIS
ACTUAL TEMP
04686-069
LOW TEMP LIMIT TMIN
When the temperature drops below the low temperature limit, TMIN can increase in the long cycle. Increasing TMIN has the effect of running the fan slower and, therefore, quieter. The long cycle diagram in Figure 66 shows the conditions that need to be true for TMIN to increase. A quick summary of those conditions and the reasons they need to be true follows. TMIN can increase if * The measured temperature falls below the low temperature limit. This means the user must choose the low limit carefully. It should not be so low that the temperature never falls below it because TMIN would never increase, and the fans would run faster than necessary. TMIN is below the high temperature limit. TMIN is never allowed to increase above the high temperature limit. As a result, the high limit should be sensibly chosen because it determines how high TMIN can go. TMIN is below the operating point temperature. TMIN should never be allowed to increase above the operating point temperature because the fans would not switch on until the temperature rose above the operating point. The temperature is above TMIN. The dynamic TMIN control is turned off below TMIN.
Figure 67. Temperature Between Operating Point and Low Temperature Limit
Because neither the operating point minus the hysteresis temperature nor the low temperature limit has been exceeded, the TMIN value is not adjusted, and the fan runs at a speed determined by the fixed TMIN and TRANGE values defined in the automatic fan speed control mode.
Example 2: Operating Point Exceeded--TMIN Reduced
*
When the measured temperature is below the operating point temperature minus the hysteresis, TMIN remains the same.
*
*
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ADT7473
THERM LIMIT HIGH TEMP LIMIT OPERATING POINT
HYSTERESIS
ACTUAL TEMP
TMIN LOW TEMP LIMIT
NO CHANGE IN TMIN HERE DUE TO ANY CYCLE BECAUSE T1(n) - T1 (n - 1) 0.25C AND T1(n) < OP = > TMIN STAYS THE SAME
DECREASE HERE DUE TO SHORT CYCLE ONLY T1(n) - T1 (n - 1) = 0.5C OR 0.75C = > TMIN DECREASES BY 1C EVERY SHORT CYCLE
DECREASE HERE DUE TO LONG CYCLE ONLY T1(n) - T1 (n - 1) 0.25C AND T1(n) > OP = > TMIN DECREASES BY 1C EVERY LONG CYCLE
Figure 68. Effect of Exceeding Operating Point Minus Hysteresis Temperature
Figure 69 shows how TMIN increases when the current temperature is above TMIN and below the low temperature limit, and TMIN is below the high temperature limit and below the operating point. Once the temperature rises above the low temperature limit, TMIN stays the same.
THERM LIMIT HIGH TEMP LIMIT OPERATING POINT
THERM LIMIT OPERATING POINT
HYSTERESIS
LOW TEMP LIMIT HIGH TEMP LIMIT TMIN
ACTUAL TEMP
04686-070
HYSTERESIS
TMIN PREVENTED FROM INCREASING
Figure 70. TMIN Adjustments Limited by the High Temperature Limit
LOW TEMP LIMIT TMIN ACTUAL TEMP
04686-071
STEP 11: MONITORING THERM
Using the operating point limit ensures that the dynamic TMIN control mode operates in the best possible acoustic position while ensuring that the temperature never exceeds the maximum operating temperature. Using the operating point limit allows TMIN to be independent of system-level issues because of its self-corrective nature. In PC design, the operating point for the chassis is usually the worst-case internal chassis temperature. The optimal operating point for the processor is determined by monitoring the thermal monitor in the Intel Pentium 4 processor. To do this, the PROCHOT output of the Pentium 4 is connected to the THERM input of the ADT7473. The operating point for the processor can be determined by allowing the current temperature to be copied to the operating point register when the PROCHOT output pulls the THERM input low on the ADT7473. This gives the maximum temperature at which the Pentium 4 can run before clock modulation occurs.
Figure 69. Increasing TMIN for Quieter Operation
Example 4: Preventing TMIN from Reaching Full Scale
Because TMIN is dynamically adjusted, it is undesirable for TMIN to reach full scale (127C) because the fan would never switch on. As a result, TMIN is allowed to vary only within a specified range: * * * The lowest possible value for TMIN is -127C (twos complement mode) or -64C (Offset 64 mode). TMIN cannot exceed the high temperature limit. If the temperature is below TMIN, the fan is switched off or runs at minimum speed and dynamic TMIN control is disabled.
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ADT7473
Enabling the THERM Trip Point as the Operating Point
Bits [4:2] of Dynamic TMIN Control Register 1 (0x36) enable/disable THERM monitoring to program the operating point.
Dynamic TMIN Control Register 1 (0x36)
Bit [7] R2T = 1, enables dynamic TMIN control on the Remote 2 temperature channel. The chosen TMIN value is dynamically adjusted based on the current temperature, operating point, and high and low limits for this zone. R2T = 0, disables dynamic TMIN control. The TMIN value chosen is not adjusted and the channel behaves as described in the Automatic Fan Control Overview section. Bit [6] LT = 1, enables dynamic TMIN control on the local temperature channel. The chosen TMIN value is dynamically adjusted based on the current temperature, operating point, and high and low limits for this zone. LT = 0, disables dynamic TMIN control. The TMIN value chosen is not adjusted and the channel behaves as described in the Automatic Fan Control Overview section. Bit [5] R1T = 1, enables dynamic TMIN control on the Remote 1 temperature channel. The chosen TMIN value is dynamically adjusted based on the current temperature, operating point, and high and low limits for this zone. R1T = 0, disables dynamic TMIN control. The TMIN value chosen is not adjusted, and the channel behaves as described in the Automatic Fan Control Overview section.
Dynamic TMIN Control Register 1 (0x36)
Bit [4] PHTR2 = 1, copies the Remote 2 current temperature to the Remote 2 operating point register, if THERM is asserted. The operating point contains the temperature at which THERM is asserted. This allows the system to run as quietly as possible without affecting system performance. PHTR2 = 0, ignores any THERM assertions. The Remote 2 operating point register reflects its programmed value. Bit [3] PHTL = 1, copies the local current temperature to the local temperature operating point register if THERM is asserted. The operating point contains the temperature at which THERM is asserted. This allows the system to run as quietly as possible without affecting system performance. PHTL = 0, ignores any THERM assertions. The local temperature operating point register reflects its programmed value. Bit [2] PHTR1 = 1, copies the Remote 1 current temperature to the Remote 1 operating point register if THERM is asserted. The operating point contains the temperature at which THERM is asserted. This allows the system to run as quietly as possible without affecting system performance. PHTR1 = 0, ignores any THERM assertions. The Remote 1 operating point register reflects its programmed value.
ENHANCING SYSTEM ACOUSTICS
Automatic fan speed control mode reacts instantaneously to changes in temperature; that is, the PWM duty cycle responds immediately to temperature change. Any impulses in temperature can cause an impulse in fan noise. For psychoacoustic reasons, the ADT7473 can prevent the PWM output from reacting instantaneously to temperature changes. Enhanced acoustic mode controls the maximum change in PWM duty cycle at a given time. The objective is to prevent the fan from cycling up and down, annoying the user.
Enabling Dynamic TMIN Control Mode
Bits [7:5] of the Dynamic TMIN Control Register 1 (0x36) enable/disable dynamic TMIN control on the temperature channels.
Acoustic Enhancement Mode Overview
Figure 71 gives a top-level overview of the automatic fan control circuitry on the ADT7473 and shows where acoustic enhancement fits in. Acoustic enhancement is intended as a postdesign tweak made by a system or mechanical engineer evaluating best settings for the system. Having determined the optimal settings for the thermal solution, the engineer can adjust the system acoustics. The goal is to implement a system that is acoustically pleasing without causing user annoyance due to fan cycling. It is important to realize that although a system might pass an acoustic noise requirement specification (for example, 36 dB), if the fan is annoying, it fails the consumer test.
Rev. A | Page 53 of 76
ADT7473
ACOUSTIC ENHANCEMENT THERMAL CALIBRATION
100%
PWM MIN RAMP CONTROL (ACOUSTIC ENHANCEMENT)
PWM CONFIG PWM GENERATOR
PWM1
TMIN REMOTE 2 = CPU TEMP
TRANGE
0% PWM MIN
THERMAL CALIBRATION
TACHOMETER 1 MEASUREMENT
100%
PWM CONFIG PWM GENERATOR
TACH1 CPU FAN SINK
MUX
0% PWM MIN
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 2 MEASUREMENT
PWM2
TMIN LOCAL = VRM TEMP
TRANGE
THERMAL CALIBRATION
PWM CONFIG PWM GENERATOR
TACH2
100%
RAMP CONTROL (ACOUSTIC ENHANCEMENT) TACHOMETER 3 AND 4 MEASUREMENT
FRONT CHASSIS PWM3
TMIN REMOTE 1 = AMBIENT TEMP
TRANGE
0%
TACH3
REAR CHASSIS
Figure 71. Acoustic Enhancement Smoothes Fan Speed Variations Under Automatic Fan Speed Control
Approaches to System Acoustic Enhancement
There are two different approaches to implementing system acoustic enhancement: temperature-centric and fan-centric. The temperature-centric approach involves smoothing transient temperatures as they are measured by a temperature source (for example, Remote 1 temperature). The temperature values used to calculate the PWM duty cycle values are smoothed, reducing fan speed variation. However, this approach causes an inherent delay in updating fan speed and causes the thermal characteristics of the system to change. It also causes the system fans to stay on longer than necessary because the fan's reaction is merely delayed. The user has no control over noise from different fans driven by the same temperature source. Consider, for example, a system in which control of a CPU cooler fan (on PWM1) and a chassis fan (on PWM2) use Remote 1 temperature. Because the Remote 1 temperature is smoothed, both fans are updated at exactly the same rate. If the chassis fan is much louder than the CPU fan, there is no way to improve its acoustics without changing the thermal solution of the CPU cooling fan. The fan-centric approach to system acoustic enhancement controls the PWM duty cycle, driving the fan at a fixed rate (for example, 6%). Each time the PWM duty cycle is updated, it is incremented by a fixed 6%. As a result, the fan ramps smoothly to its newly calculated speed. If the temperature starts to drop, the PWM duty cycle immediately decreases by 6% at every update. Therefore, the fan ramps smoothly up or down without inherent system delay. Consider, for example, controlling the same CPU cooler fan (on PWM1) and chassis fan (on PWM2) using Remote 1 temperature. The TMIN and TRANGE settings have already been defined in automatic fan speed control mode, that is, thermal characterization of the control loop has been optimized. Here, the chassis fan is noisier than the CPU cooling fan. Using the fan-centric approach, PWM2 can be placed into acoustic enhancement mode independently of PWM1. The acoustics of the chassis fan can, therefore, be adjusted without affecting the acoustic behavior of the CPU cooling fan, even though both fans are controlled by Remote 1 temperature. The fan-centric approach is how acoustic enhancement works on the ADT7473.
Enabling Acoustic Enhancement for Each PWM Output
Enhance Acoustics Register 1 (0x62)
Bit 3 = 1, enables acoustic enhancement on PWM1 output
Enhance Acoustics Register 2 (0x63)
Bit 7 = 1, enables acoustic enhancement on PWM2 output Bit 3 = 1, enables acoustic enhancement on PWM3 output
Effect of Ramp Rate on Enhanced Acoustics Mode
The PWM signal driving the fan has a period, T, given by the PWM drive frequency, f, because T = 1/f. For a given PWM period, T, the PWM period is subdivided into 255 equal time slots. One time slot corresponds to the smallest possible increment in the PWM duty cycle. A PWM signal of 33% duty cycle is, therefore, high for 1/3 x 255 time slots and low for 2/3 x 255 time slots. Therefore, a 33% PWM duty cycle corresponds to a signal that is high for 85 time slots and low for 170 time slots.
Rev. A | Page 54 of 76
04686-073
ADT7473
PWM_OUT 33% DUTY CYCLE 85 TIME SLOTS 170 TIME SLOTS PWM OUTPUT (ONE PERIOD) = 255 TIME SLOTS
04686-074
STEP 12: RAMP RATE FOR ACOUSTIC ENHANCEMENT
The optimal ramp rate for acoustic enhancement can be found through system characterization after the thermal optimization has been finished. The effect of each ramp rate should be logged, if possible, to determine the best setting for a given solution.
Figure 72. 33% PWM Duty Cycle Represented in Time Slots
The ramp rates in the enhanced acoustics mode are selectable from the values 1, 2, 3, 5, 8, 12, 24, and 48. The ramp rates are discrete time slots. For example, if the ramp rate is 8, then eight time slots are added to the PWM high duty cycle each time the PWM duty cycle needs to be increased. If the PWM duty cycle value needs to be decreased, it is decreased by eight time slots. Figure 73 shows how the enhanced acoustics mode algorithm operates.
READ TEMPERATURE
Enhance Acoustics Register 1 (0x62)
Bits [2:0] ACOU, select the ramp rate for PWM1. 000 = 1 time slot = 35 sec 001 = 2 time slots = 17.6 sec 010 = 3 time slots = 11.8 sec 011 = 5 time slots = 7 sec 100 = 8 time slots = 4.4 sec 101 = 12 time slots = 3 sec 110 = 24 time slots = 1.6 sec 111 = 48 time slots = 0.8 sec
CALCULATE NEW PWM DUTY CYCLE
Enhance Acoustics Register 2 (0x63)
IS NEW PWM VALUE > PREVIOUS VALUE? YES INCREMENT PREVIOUS PWM VALUE BY RAMP RATE NO DECREMENT PREVIOUS PWM VALUE BY RAMP RATE
Bits [2:0] ACOU3, select the ramp rate for PWM3. 000 = 1 time slot = 35 sec 001 = 2 time slots = 17.6 sec 010 = 3 time slots = 11.8 sec 011 = 5 time slots = 7 sec 100 = 8 time slots = 4.4 sec 101 = 12 time slots = 3 sec 110 = 24 time slots = 1.6 sec 111 = 48 time slots = 0.8 sec Bits [6:4] ACOU2, select the ramp rate for PWM2. 000 = 1 time slot = 35 sec 001 = 2 time slots = 17.6 sec 010 = 3 time slots = 11.8 sec 011 = 5 time slots = 7 sec 100 = 8 time slots = 4.4 sec 101 = 12 time slots = 3 sec 110 = 24 time slots = 1.6 sec 111 = 48 time slots = 0.8 sec Another way to view the ramp rates is to measure the time it takes for the PWM output to ramp up from 0% to 100% duty cycle for an instantaneous change in temperature. This can be tested by putting the ADT7473 into manual mode and changing the PWM output from 0% to 100% PWM duty cycle. The PWM output takes 35 seconds to reach 100% when a ramp rate of 1 time slot is selected.
Figure 73. Enhanced Acoustics Algorithm
The enhanced acoustics mode algorithm calculates a new PWM duty cycle based on the temperature measured. If the new PWM duty cycle value is greater than the previous PWM value, then the previous PWM duty cycle value is incremented by either 1, 2, 3, 5, 8, 12, 24, or 48 time slots, depending on the settings of the enhance acoustics registers. If the new PWM duty cycle value is less than the previous PWM value, the previous PWM duty cycle is decremented by 1, 2, 3, 5, 8, 12, 24, or 48 time slots. Each time the PWM duty cycle is incremented or decremented, its value is stored as the previous PWM duty cycle for the next comparison. A ramp rate of 1 corresponds to one time slot, which is 1/255 of the PWM period. In enhanced acoustics mode, incrementing or decrementing by 1 changes the PWM output by 1/255 x 100%.
04686-075
Rev. A | Page 55 of 76
ADT7473
Figure 74 shows remote temperature plotted against PWM duty cycle for enhanced acoustics mode. The ramp rate is set to 48, which corresponds to the fastest ramp rate. Assume that a new temperature reading is available every 115 ms. With these settings, it takes approximately 0.76 seconds to go from 33% duty cycle to 100% duty cycle (full speed). Even though the temperature increases very rapidly, the fan ramps up to full speed gradually.
140 RTEMP (C) 120 100 80 80 60 60 PWM CYCLE (%) 40 20 0 0 20
04686-076
Figure 76 shows the PWM output response for a ramp rate of 2. In this instance, the fan took about 17.6 seconds to reach full running speed.
140 RTEMP (C) 120 100 120
100
120
80 80
100
PWM DUTY CYCLE (%) 60
60
40 40 20 0 0 TIME (s) 20
04686-078 04686-079
40
17.6
0
Figure 76. Enhanced Acoustics Mode with Ramp Rate = 2
TIME (s)
0 0.76
Figure 74. Enhanced Acoustics Mode with Ramp Rate = 48
Figure 75 shows how changing the ramp rate from 48 to 8 affects the control loop. The overall response of the fan is slower. Because the ramp rate is reduced, it takes longer for the fan to achieve full running speed. In this case, it takes approximately 4.4 seconds for the fan to reach full speed.
120 RTEMP (C) 100 120 100 140
Figure 77 shows how the control loop reacts to temperature with the slowest ramp rate. The ramp rate is set to 1, while all other control parameters remain the same. With the slowest ramp rate selected, it takes 35 seconds for the fan to reach full speed.
120 RTEMP (C) 100 120 100 80 80 60 PWM DUTY CYCLE (%) 40 60 40 20 0 140
80 PWM DUTY CYCLE (%) 60
80
20
60 40 40 20 20 0
0 0 TIME (s) 35
Figure 77. Enhanced Acoustics Mode with Ramp Rate = 1
0 0
TIME (s)
4.4
Figure 75. Enhanced Acoustics Mode with Ramp Rate = 8
As Figure 74 to Figure 77 show, the rate at which the fan reacts to temperature change is dependent on the ramp rate selected in the enhanced acoustics registers. The higher the ramp rate, the faster the fan reaches the newly calculated fan speed.
04686-077
Rev. A | Page 56 of 76
ADT7473
Figure 78 shows the behavior of the PWM output as temperature varies. As the temperature increases, the fan speed ramps up. Small drops in temperature do not affect the ramp-up function because the newly calculated fan speed is still higher than the previous PWM value. Enhanced acoustics mode allows the PWM output to be made less sensitive to temperature variations. This is dependent on the ramp rate selected and programmed into the enhanced acoustics registers.
90 80 70 60 50 40 30 20
04686-080
The following sections list the ramp-up times when the SLOW bit is set for each PWM output.
Enhance Acoustics Register 1 (0x62)
Bits [2:0] ACOU, select the ramp rate for PWM1. 000 = 140 sec 001 = 70.4 sec 010 = 47.2 sec 011 = 28 sec 100 = 17.6 sec 101 = 12 sec 110 = 6.4 sec 111 = 3.2 sec
PWM DUTY CYCLE (%)
RTEMP (C)
Enhance Acoustics Register 2 (0x63)
Bits [2:0] ACOU3, select the ramp rate for PWM3. 000 = 140 sec 001 = 70.4 sec 010 = 47.2 sec 011 = 28 sec 100 = 17.6 sec 101 = 12 sec 110 = 6.4 sec 111 = 3.2 sec Bits [6:4] ACOU2, select the ramp rate for PWM2. 000 = 140 sec 001 = 70.4 sec 010 = 47.2 sec 011 = 28 sec 100 = 17.6 sec 101 = 12 sec 110 = 6.4 sec 111 = 3.2 sec
10 0
Figure 78. How Fan Reacts to Temperature Variation in Enhanced Acoustics Mode
Slower Ramp Rates
The ADT7473 can be programmed for much longer ramp times by slowing the ramp rates. Each ramp rate can be slowed by a factor of 4.
PWM1 Configuration Register (0x5C)
Bit [3] SLOW, 1 slows the ramp rate for PWM1 by 4.
PWM2 Configuration Register (0x5D)
Bit [3] SLOW, 1 slows the ramp rate for PWM2 by 4.
PWM3 Configuration Register (0x5E)
Bit [3] SLOW, 1 slows the ramp rate for PWM3 by 4.
Rev. A | Page 57 of 76
ADT7473 REGISTER TABLES
Table 17. ADT7473 Registers
Address 0x21 0x22 0x25 0x26 0x27 0x28 0x29 0x2A 0x2B 0x2C 0x2D 0x2E 0x2F 0x30 0x31 0x32 0x33 0x34 0x35 0x36 0x37 0x38 0x39 0x3A 0x3D 0x3E 0x40 0x41 0x42 0x46 0x47 0x48 0x49 0x4E 0x4F R/W R R R R R R R R R R R R R R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R R R/W R R R/W R/W R/W R/W R/W R/W Description VCCP Reading VCC Reading Remote 1 Temperature Local Temperature Remote 2 Temperature TACH1 Low Byte TACH1 High Byte TACH2 Low Byte TACH2 High Byte TACH3 Low Byte TACH3 High Byte TACH4 Low Byte TACH4 High Byte PWM1 Current Duty Cycle PWM2 Current Duty Cycle PWM3 Current Duty Cycle Remote 1 Operating Point Local Temp Operating Point Remote 2 Operating Point Dynamic TMIN Control Reg. 1 Dynamic TMIN Control Reg. 2 PWM1 Max Duty Cycle PWM2 Max Duty Cycle PWM3 Max Duty Cycle Device ID Register Company ID Number Configuration Register 1 Interrupt Status Register 1 Interrupt Status Register 2 VCCP Low Limit VCCP High Limit VCC Low Limit VCC High Limit Remote 1 Temp Low Limit Remote 1 Temp High Limit Bit 7 9 9 9 9 9 7 15 7 15 7 15 7 15 7 7 7 7 7 7 R2T CYR2 7 7 7 7 7 RES OOL D2 7 7 7 7 7 7 Bit 6 8 8 8 8 8 6 14 6 14 6 14 6 14 6 6 6 6 6 6 LT CYR2 6 6 6 6 6 TODIS R2T D1 6 6 6 6 6 6 Bit 5 7 7 7 7 7 5 13 5 13 5 13 5 13 5 5 5 5 5 5 R1T CYL 5 5 5 5 5 FSPDIS LT F4P 5 5 5 5 5 5 Bit 4 6 6 6 6 6 4 12 4 12 4 12 4 12 4 4 4 4 4 4 PHTR2 CYL 4 4 4 4 4 Vx1 R1T FAN3 4 4 4 4 4 4 Bit 3 5 5 5 5 5 3 11 3 11 3 11 3 11 3 3 3 3 3 3 PHTL CYL 3 3 3 3 3 FSPD RES FAN2 3 3 3 3 3 3 Bit 2 4 4 4 4 4 2 10 2 10 2 10 2 10 2 2 2 2 2 2 PHTR1 CYR1 2 2 2 2 2 RDY VCC FAN1 2 2 2 2 2 2 Bit 1 3 3 3 3 3 1 9 1 9 1 9 1 9 1 1 1 1 1 1 VCCPLO CYR1 1 1 1 1 1 LOCK VCCP OVT 1 1 1 1 1 1 Bit 0 2 2 2 2 2 0 8 0 8 0 8 0 8 0 0 0 0 0 0 CYR2 CYR1 0 0 0 0 0 STRT RES RES 0 0 0 0 0 0 Default 0x00 0x00 0x01 0x01 0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0xA4 0xA4 0xA4 0x00 0x00 0xFF 0xFF 0xFF 0x73 0x41 0x01 0x00 0x00 0x00 0xFF 0x00 0xFF 0x01 0xFF Yes Yes Yes Yes Yes Yes Lockable?
Rev. A | Page 58 of 76
ADT7473
Address 0x50 0x51 0x52 0x53 0x54 0x55 0x56 0x57 0x58 0x59 0x5A 0x5B 0x5C R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W Description Local Temp Low Limit Local Temp High Limit Remote 2 Temp Low Limit Remote 2 Temp High Limit TACH1 Minimum Low Byte TACH1 Minimum High Byte TACH2 Minimum Low Byte TACH2 Minimum High Byte TACH3 Minimum Low Byte TACH3 Minimum High Byte TACH4 Minimum Low Byte TACH4 Minimum High Byte PWM1 Configuration Register PWM2 Configuration Register PWM3 Configuration Register Remote 1 TRANGE/PWM 1 Frequency Local TRANGE/PWM 2 Frequency Remote 2 TRANGE/PWM 3 Frequency Enhance Acoustics Reg. 1 Enhance Acoustics Reg. 2 PWM1 Min Duty Cycle PWM2 Min Duty Cycle PWM3 Min Duty Cycle Remote 1 Temp TMIN Local Temp TMIN Remote 2 Temp TMIN Remote 1 THERM Temp Limit Local THERM Temp Limit Bit 7 7 7 7 7 7 15 7 15 7 15 7 15 BHVR Bit 6 6 6 6 6 6 14 6 14 6 14 6 14 BHVR Bit 5 5 5 5 5 5 13 5 13 5 13 5 13 BHVR Bit 4 4 4 4 4 4 12 4 12 4 12 4 12 INV Bit 3 3 3 3 3 3 11 3 11 3 11 3 11 SLOW Bit 2 2 2 2 2 2 10 2 10 2 10 2 10 SPIN Bit 1 1 1 1 1 1 9 1 9 1 9 1 9 SPIN Bit 0 0 0 0 0 0 8 0 8 0 8 0 8 SPIN Default 0x01 0xFF 0x01 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0x82 Yes Lockable?
0x5D
R/W
BHVR
BHVR
BHVR
INV
SLOW
SPIN
SPIN
SPIN
0x82
Yes
0x5E
R/W
BHVR
BHVR
BHVR
INV
SLOW
SPIN
SPIN
SPIN
0x82
Yes
0x5F
R/W
RANGE
RANGE
RANGE
RANGE
HF/LF Fan 1 HF/LF Fan 2 HF/LF Fan 3
FREQ
FREQ
FREQ
0xCC
Yes
0x60
R/W
RANGE
RANGE
RANGE
RANGE
FREQ
FREQ
FREQ
0xCC
Yes
0x61
R/W
RANGE
RANGE
RANGE
RANGE
FREQ
FREQ
FREQ
0xCC
Yes
0x62 0x63 0x64 0x65 0x66 0x67 0x68 0x69 0x6A 0x6B
R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W
MIN3 EN2 7 7 7 7 7 7 7 7
MIN2 ACOU2 6 6 6 6 6 6 6 6
MIN1 ACOU2 5 5 5 5 5 5 5 5
SYNC ACOU2 4 4 4 4 4 4 4 4
EN1 EN3 3 3 3 3 3 3 3 3
ACOU ACOU3 2 2 2 2 2 2 2 2
ACOU ACOU 3 1 1 1 1 1 1 1 1
ACOU ACOU3 0 0 0 0 0 0 0 0
0x00 0x00 0x80 0x80 0x80 0x9A 0x9A 0x9A 0xA4 0xA4
Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes
Rev. A | Page 59 of 76
ADT7473
Address 0x6C 0x6D R/W R/W R/W Description Remote 2 THERM Temp Limit Remote 1 and Local Temp/TMIN Hysteresis Remote 2 Temp/TMIN Hysteresis XNOR Tree Test Enable Remote 1 Temperature Offset Local Temperature Offset Remote 2 Temperature Offset Configuration Register 2 Interrupt Mask Register 1 Interrupt Mask Register 2 Extended Resolution 1 Extended Resolution 2 Configuration Register 3 THERM Timer Status Register THERM Timer Limit Register TACH Pulses per Revolution Configuration Register 5 Configuration Register 4 Bit 7 7 HYSR1 Bit 6 6 HYSR1 Bit 5 5 HYSR1 Bit 4 4 HYSR1 Bit 3 3 HYSL Bit 2 2 HYSL Bit 1 1 HYSL Bit 0 0 HYSL Default 0xA4 0x44 Lockable? Yes Yes
0x6E
R/W
HYSR2
HYSR2
HYSR2
HYRS
RES
RES
RES
RES
0x40
Yes
0x6F 0x70
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
R/W
SHDN
CONV
ATTN
AVG
FAN3 Detect RES FAN2 VCCP TDM1 FAST TMR LIMT FAN2 GPIOP Max/ Full on THERM
FAN2 Detect VCC FAN1 VCCP TDM1 BOOST TMR LIMT FAN2 GPIOD THERM Disable
FAN1 Detect VCCP OVT RES RES THERM TMR LIMT FAN1
Temp Offset
FAN Presence DT
RES RES RES RES ALERT Enable ASRT/TMRO LIMT FAN1
TWOS COMPL
0x00
Yes
0x74 0x75 0x76 0x77 0x78 0x79 0x7A 0x7B 0x7C 0x7D
R/W R/W R/W R/W R/W R R/W R/W R/W R/W
OOL D2 RES TDM2 DC4 TMR LIMT FAN4
R2 THERM
R2T D1 RES TDM2 DC3 TMR LIMT FAN4
Local THERM
LT F4P VCC LTMP DC2 TMR LIMT FAN3
R1 THERM
R1T FAN3 VCC LTMP DC1 TMR LIMT FAN3 RES RES
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0X55 0x00 0x00 Yes Yes Yes
RES
BpAtt VCCP
RES
PIN9 FUNC
PIN9FUNC
0x7E 0x7F
R R
Test Register 1 Test Register 2
Do not write to these registers Do not write to these registers
0x00 0x00
Yes Yes
Table 18. Voltage Reading Registers (Power-On Default = 0x00)1
Register Address 0x21 0x22
1
R/W Read only Read only
Description Reflects the voltage measurement at the VCCP input on Pin 14 (8 MSBs of reading).2 Reflects the voltage measurement at the VCC input on Pin 3 (8 MSBs of reading).3
If the extended resolution bits of these readings are also being read, the extended resolution registers (Register 0x76 and Register 0x77) must be read first. Once the extended resolution registers have been read, the associated MSB reading registers are frozen until read. Both the extended resolution registers and the MSB registers are frozen. 2 If VCCPLo (Bit 1 of the Dynamic TMIN Control Register 1, 0x36) is set, VCCP can control the sleep state of the ADT7473. 3 VCC (Pin 3) is the supply voltage for the ADT7473.
Rev. A | Page 60 of 76
ADT7473
Table 19. Temperature Reading Registers (Power-On Default = 0x01)1, 2
Register Address 0x25 0x26 0x27
1 2
R/W Read only Read only Read only
Description Remote 1 temperature reading3, 4 (8 MSB of reading). Local temperature reading (8 MSB of reading). Remote 2 temperature reading (8 MSB of reading).
These temperature readings can be in twos complement or Offset 64 format; this interpretation is determined by Bit 0 of Configuration Register 5 (0x7C). If the extended resolution bits of these readings are also being read, the extended resolution registers (Reg. 0x76, 0x77) must be read first. Once the extended resolution registers have been read, all associated MSB reading registers are frozen until read. Both the extended resolution registers and the MSB registers are frozen. 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 20. 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 (Register 0x7B). This allows the fan speed to be accurately measured. Because a valid fan tachometer reading requires that two bytes are read, the low byte must be read first. Both the low and high bytes are then frozen until read. At power-on, these registers contain 0x0000 until 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 a fan is one of the following: * Stalled or blocked (object jamming the fan). * Failed (internal circuitry destroyed). Not populated. (The ADT7473 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 21. Current PWM Duty Cycle Registers (Power-On Default = 0x00)1
Register Address 0x30 0x31 0x32
1
R/W R/W R/W R/W
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 ADT7473 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 start up, these registers report back 0x00. In software mode, the PWM duty cycle outputs can be set to any duty cycle value by writing to these registers.
Table 22. Operating Point Registers (Power-On Default = 0xA4)1, 2, 3
Register Address 0x33 0x34 0x35
1 2 3
R/W3 R/W R/W R/W
Description Remote 1 operating point register (default = 100C). Local temperature operating point register (default = 100C). Remote 2 operating point register (default = 100C).
These registers set the target operating point for each temperature channel when the dynamic TMIN control feature is enabled. The fans being controlled are adjusted to maintain temperature about an operating point. 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. A | Page 61 of 76
ADT7473
Table 23. Register 0x36--Dynamic TMIN Control Register 1 (Power-On Default = 0x00)1
Bit [0] Name CYR2 R/W R/W Description MSB of 3-bit remote 2 cycle value. The other two bits of the code reside in Dynamic TMIN Control Register 2 (Reg. 0x37). These three bits define the delay time between making subsequent TMIN adjustments in the control loop, in terms of the number of monitoring cycles. The system has associated thermal time constants that need to be found to optimize the response of fans and the control loop. VCCPLO = 1. When the power is supplied from 3.3 V STANDBY and the core voltage (VCCP) drops below its VCCP low limit value (Register 0x46), the following occurs: * Status Bit 1 in Interrupt Status Register 1 is set. * SMBALERT is generated, if enabled. * PROCHOT monitoring is disabled. * Dynamic TMIN control is disabled. * The device is prevented from entering shutdown. * Everything is re-enabled once VCCP increases above the VCCP low limit. PHTR1 = 1 copies the Remote 1 current temperature to the Remote 1 operating point register if THERM is asserted. The operating point contains the temperature at which THERM is asserted, allowing the system to run as quietly as possible without affecting system performance. PHTR1 = 0 ignores any THERM assertions on the THERM pin. The Remote 1 operating point register reflects its programmed value. PHTL = 1 copies the local channel's current temperature to the local operating point register if THERM is asserted. The operating point contains the temperature at which THERM is asserted. This allows the system to run as quietly as possible without affecting system performance. PHTL = 0 ignores any THERM assertions on the THERM pin. The local temperature operating point register reflects its programmed value. PHTR2 = 1 copies the Remote 2 current temperature to the Remote 2 operating point register if THERM is asserted. The operating point contains the temperature at which THERM is asserted, allowing the system to run as quietly as possible without affecting system performance. PHTR2 = 0 ignores any THERM assertions on the THERM pin. The Remote 2 operating point register reflects its programmed value. R1T = 1 enables dynamic TMIN control on the Remote 1 temperature channel. The chosen TMIN value is dynamically adjusted based on the current temperature, operating point, and high and low limits for this zone. R1T = 0 disables dynamic TMIN control. The TMIN value chosen is not adjusted, and the channel behaves as described in the Fan Speed Control section. LT=1 enables dynamic TMIN control on the local temperature channel. The chosen TMIN value is dynamically adjusted based on the current temperature, operating point, and high and low limits for this zone. LT = 0 disables dynamic TMIN control. The TMIN value chosen is not adjusted, and the channel behaves as described in the Fan Speed Control section. R2T = 1 enables dynamic TMIN control on the Remote 2 temperature channel. The chosen TMIN value is dynamically adjusted based on the current temperature, operating point, and high and low limits for this zone. R2T = 0 disables dynamic TMIN control. The TMIN value chosen is not adjusted and the channel behaves as described in the Fan Speed Control section.
[1]
VCCPLO
R/W
[2]
PHTR1
R/W
[3]
PHTL
R/W
[4]
PHTR2
R/W
[5]
R1T
R/W
[6]
LT
R/W
[7]
R2T
R/W
1
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any subsequent attempts to write to this register fail.
Rev. A | Page 62 of 76
ADT7473
Table 24. Register 0x37--Dynamic TMIN Control Register 2 (Power-On Default = 0x00)1
Bit [2:0] Name CYR1 R/W R/W Description 3-bit remote 1 cycle value. These three bits define the delay time between making subsequent TMIN adjustments in the control loop for the Remote 1 channel, in terms of number of monitoring cycles. The system has associated thermal time constants that need to be found to optimize the response of fans and the control loop. Decrease Cycle Increase Cycle 8 cycles (1 sec) 16 cycles (2 sec) 16 cycles (2 sec) 32 cycles (4 sec) 32 cycles (4 sec) 64 cycles (8 sec) 64 cycles (8 sec) 128 cycles (16 sec) 128 cycles (16 sec) 256 cycles (32 sec) 256 cycles (32 sec) 512 cycles (64 sec) 512 cycles (64 sec) 1024 cycles (128 sec) 2048 cycles (256 sec) 1024 cycles (128 sec) 3-bit local temperature cycle value. These three bits define the delay time between making subsequent TMIN adjustments in the control loop for the local temperature channel, in terms of number of monitoring cycles. The system has associated thermal time constants that need to be found to optimize the response of fans and the control loop. Decrease Cycle Increase Cycle 8 cycles (1 sec) 16 cycles (2 sec) 16 cycles (2 sec) 32 cycles (4 sec) 32 cycles (4 sec) 64 cycles (8 sec) 64 cycles (8 sec) 128 cycles (16 sec) 128 cycles (16 sec) 256 cycles (32 sec) 256 cycles (32 sec) 512 cycles (64 sec) 512 cycles (64 sec) 1024 cycles (128 sec) 2048 cycles (256 sec) 1024 cycles (128 sec) 2 LSBs of 3-bit remote 2 cycle value. The MSB of the 3-bit code resides in Dynamic TMIN Control Register 1 (Register 0x36). These three bits define the delay time between making subsequent TMIN adjustments in the control loop for the Remote 2 channel, in terms of number of monitoring cycles. The system has associated thermal time constants that need to be found to optimize the response of fans and the control loop. Decrease Cycle Increase Cycle 8 cycles (1 sec) 16 cycles (2 sec) 16 cycles (2 sec) 32 cycles (4 sec) 32 cycles (4 sec) 64 cycles (8 sec) 64 cycles (8 sec) 128 cycles (16 sec) 128 cycles (16 sec) 256 cycles (32 sec) 256 cycles (32 sec) 512 cycles (64 sec) 512 cycles (64 sec) 1024 cycles (128 sec) 1024 cycles (128 sec) 2048 cycles (256 sec)
[5:3]
CYL
Bits 000 001 010 011 100 101 110 111 R/W
[7:6]
CYR2
Bits 000 001 010 011 100 101 110 111 R/W
Bits 000 001 010 011 100 101 110 111
1
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Any subsequent attempts to write to this register fail.
Table 25. Maximum PWM Duty Cycle Registers (Power-On Default = 0xFF)1, 2, 3
Register Address 0x38 0x39 0x3A
1 2
R/W2 R/W R/W R/W
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. These registers become read-only when the Configuration Register 1 lock bit is set to 1. Any subsequent attempts to write to this register fail. 3 If Bit 3 of Configuration Register 4 (0x7D) is set, then on a THERM overtemperature event, fans go to their maximum programmed PWM value as programmed here. If Bit 3 of Configuration Register 4 (0x7D) is 0, then on a THERM overtemperature event, fans go to 100% PWM.
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ADT7473
Table 26. Register 0x40--Configuration Register 1 (Power-On Default = 0x01)
Bit [0] Name STRT R/W R/W Description Logic 1 enables monitoring and PWM control outputs based on the limit settings programmed. Logic 0 disables monitoring and PWM control based on the default power-up limit settings. This bit is not locked when Bit 1 (LOCK bit) has been written. This bit remains writable after lock bit is set. Logic 1 locks all limit values to their current settings. Once this bit is set, all lockable registers become readonly and cannot be modified until the ADT7473 is powered down and powered up again. This prevents rogue programs, such as viruses, from modifying critical system limit settings. (This is a lockable bit.) This bit is set to 1 by the ADT7473 to indicate only that the device is fully powered up and ready to begin system monitoring. When set to 1, this bit runs all fans at maximum speed as programmed in the maximum PWM 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 ADT7473 is configured to measure current from an ADI ADOPT(R) VRM controller and to measure the CPU's core voltage. This bit allows monitoring software to display CPU watts usage. (This is a lockable bit.) Logic 1 disables fan spin-up for two TACH pulses. Instead, the PWM outputs go high for the entire fan spin-up timeout selected. When this bit is set to 1, the SMBus timeout feature is enabled. This allows the ADT7473 to be used with SMBus controllers that cannot handle SMBus timeouts. (This is a lockable bit.) Reserved.
[1]
LOCK
Write once
[2] [3] [4]
RDY FSPD VxI
Read only R/W R/W
[5] [6] [7]
FSPDIS TODIS RES
R/W R/W
Table 27. Register 0x41--Interrupt Status Register 1 (Power-On Default = 0x00)
Bit [1] [2] [4] [5] [6] [7] Name VCCP VCC RIT LT R2T OOL R/W Read only Read only Read only Read only Read only Read only Description VCCP = 1 indicates 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 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. R1T = 1 indicates 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 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 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 an out-of-limit event has been latched in Interrupt Status Register 2 (0x42). 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 saves the need to read Interrupt Status Register 2 every interrupt or polling cycle.
Table 28. Register 0x42--Interrupt Status Register 2 (Power-On Default = 0x00)
Bit [1] [2] [3] [4] [5] Name OVT FAN1 FAN2 FAN3 F4P R/W Read only Read only Read only Read only Read only R/W Read only [6] [7] D1 D2 Read only Read only Description OVT = 1 indicates one of the THERM overtemperature limits is exceeded. This bit is cleared on a read of the status register when the temperature drops below THERM - THYST. FAN1 = 1 indicates Fan 1 has dropped below minimum speed or has stalled. This bit is not set when the PWM1 output is off. FAN2 = 1 indicates Fan 2 has dropped below minimum speed or has stalled. This bit is not set when the PWM2 output is off. FAN3 = 1 indicates Fan 3 has dropped below minimum speed or has stalled. This bit is not set when the PWM3 output is off. F4P = 1 indicates Fan 4 has dropped below minimum speed or has stalled. This bit is not set when the PWM3 output is off. When Pin 9 is programmed as a GPIO output, writing to this bit determines the logic output of the GPIO. If Pin 9 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 (Reg. 0x7A). D1 = 1 indicates either an open or short circuit on the Thermal Diode 1 inputs. D2 = 1 indicates either an open or short circuit on the Thermal Diode 2 inputs.
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ADT7473
Table 29. Voltage Limit Registers1
Register Address 0x46 0x47 0x48 0x49
1 2
R/W R/W R/W R/W R/W
Description2 VCCP low limit. VCCP high limit. VCC low limit. VCC high limit.
Power-On Default 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).
Table 30. Temperature Limit Registers1
Register Address 0x4E 0x4F 0x50 0x51 0x52 0x53
1
R/W R/W R/W R/W R/W R/W R/W
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 0x01 0xFF 0x01 0xFF 0x01 0xFF
Exceeding any of these temperature limits by 1C causes the appropriate status bit to be set in the interrupt status register. Setting the Configuration Register 1 lock bit has no effect on these registers. 2 High Limits: An interrupt is generated when a value exceeds its high limit (> comparison). Low Limits: An interrupt is generated when a value is equal to or below its low limit ( comparison).
Table 31. Fan Tachometer Limit Registers1
Register Address 0x54 0x55 0x56 0x57 0x58 0x59 0x5A 0x5B
1
R/W R/W R/W R/W R/W R/W R/W R/W R/W
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 slowly or has stalled. The appropriate status bit is set in Interrupt Status Register 2 to indicate the fan failure. Setting the Configuration Register 1 lock bit has no effect on these registers.
Table 32. Register 0x55--TACH1 Minimum High Byte (Power-On Default = 0xFF)
Bit [4:0] [7:5] Name Reserved SCADC R/W Read-only R/W Description These bits are reserved when Bit 6 of Configuration Register 2 (0x73) is set (single-channel ADC mode). Otherwise, these bits represent Bits [4:0] of the TACH1 minimum high byte. When Bit 6 of Configuration Register 2 (0x73) is set (single-channel ADC mode), these bits are used to select the only channel from which the ADC makes measurements. Otherwise, these bits represent Bits [7:5] of the TACH1 minimum high byte.
Table 33. PWM Configuration Registers
Register Address 0x5C 0x5D 0x5E
1
R/W1 R/W R/W R/W
Description PWM1 configuration. PWM2 configuration. PWM3 configuration.
Power-On Default 0x82 0x82 0x82
These registers become read-only when the Configuration Register 1 lock bit is set. Any further attempts to write to these registers have no effect.
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ADT7473
Table 34. Register 0x5C, Register 0x5D, and Register 0x5E--Configuration Registers (Power-On Default = 0x82)
Bit [2:0] Name SPIN R/W R/W Description These bits control the start-up 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 start-up timeout period, then 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, then the Interrupt Status Register 2 bit is not set, even if the fan has not started. 000 = No start-up timeout. 001 = 100 ms. 010 = 250 ms (default). 011 = 400 ms. 100 = 667 ms. 101 = 1 sec. 110 = 2 sec. 111 = 4 sec. SLOW = 1 makes the ramp rates for acoustic enhancement four times longer. This bit inverts the PWM output. The default is 0, which corresponds to a logic high output for 100% duty cycle. Setting this bit to 1 inverts the PWM output, so 100% duty cycle corresponds to a logic low output. These bits assign each fan to a particular temperature sensor for localized cooling. 000 = Remote 1 temperature controls PWMx (automatic fan control mode). 001 = Local temperature controls PWMx (automatic fan control mode). 010 = Remote 2 temperature controls PWMx (automatic fan control mode). 011 = PWMx runs full speed. 100 = PWMx disabled (default). 101 = Fastest speed calculated by local and Remote 2 temperature controls PWMx. 110 = Fastest speed calculated by all three temperature channel controls PWMx. 111 = Manual mode. PWM duty cycle registers (Register 0x30 to Register 0x32) become writable.
[3] [4]
SLOW INV
R/W R/W
[7:5]
BHVR
R/W
Table 35. TEMP TRANGE/PWM Frequency Registers
Register Address 0x5F 0x60 0x61
1
R/W1 R/W R/W R/W
Description Remote 1 TRANGE/PWM1 frequency. Local temperature TRANGE/PWM2 frequency. Remote 2 TRANGE/PWM3 frequency.
Power-On Default 0xCC 0xCC 0xCC
These registers become read-only when the Configuration Register 1 lock bit is set. Any further attempts to write to these registers have no effect.
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ADT7473
Table 36. Register 0x5F, Register 0x60, and Register 0x61--TEMP TRANGE/PWM Frequency Registers (Power-On Default = 0xCC)
Bit [2:0] Name FREQ R/W R/W Description These bits control the PWMx frequency. 000 = 11.0 Hz. 001 = 14.7 Hz. 010 = 22.1 Hz. 011 = 29.4 Hz. 100 = 35.3 Hz (default). 101 = 44.1 Hz. 110 = 58.8 Hz. 111 = 88.2 Hz. HF/LF =1, enables high frequency PWM output for 4-wire fans. Once enabled, 3-wire fan-specific settings have no effect. 0x5F, HF/LF = 1 enables high frequency mode for Fan 1. 0x60, HF/LF = 1 enables high frequency mode for Fan 2. 0x61, HF/LF = 1 enables high frequency mode for Fan 3. These bits determine the PWM duty cycle vs. the temperature slope for automatic fan control. 0000 = 2C. 0001 = 2.5C. 0010 = 3.33C. 0011 = 4C. 0100 = 5C. 0101 = 6.67C. 0110 = 8C. 0111 = 10C. 1000 = 13.33C. 1001 = 16C. 1010 = 20C. 1011 = 26.67C. 1100 = 32C (default). 1101 = 40C. 1110 = 53.33C. 1111 = 80C.
[3]
HF/LF
R/W
[7:4]
RANGE
R/W
Rev. A | Page 67 of 76
ADT7473
Table 37. Register 0x62--Enhance Acoustics Register 1 (Power-On Default = 0x00)
Bit [2:0] Name ACOU R/W1 R/W Description These bits select the ramp rate applied to the PWM1 output. Instead of PWM1 jumping instantaneously to its newly calculated speed, PWM1 ramps gradually at the rate determined by these bits. This feature enhances the acoustics of the fan being driven by the PWM1 output. Time Slot Increase Time for 33% to 100% 000 = 1 35 sec 001 = 2 17.6 sec 010 = 3 11.8 sec 011 = 4 7 sec 100 = 8 4.4 sec 101 = 12 3 sec 110 = 24 1.6 sec 111 = 48 0.8 sec When this bit is 1, acoustic enhancement is enabled on PWM1 output. SYNC = 1 synchronizes fan speed measurements on TACH2, TACH3, and TACH4 to PWM3. This allows up to three fans to be driven from PWM3 output and their speeds to be measured. SYNC = 0 synchronizes only TACH3 and TACH4 to PWM3 output. When the ADT7473 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 ADT7473 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 ADT7473 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
R/W R/W
[5]
MIN
R/W
[6]
MIN
R/W
[7]
MIN3
R/W
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. A | Page 68 of 76
ADT7473
Table 38. Register 0x63--Enhance Acoustics Register 2 (Power-On Default = 0x00)
Bit [2:0] Name ACOU3 R/W1 R/W Description These bits select the ramp rate applied to the PWM3 output. Instead of PWM3 jumping instantly to its newly calculated speed, PWM3 ramps gradually at the rate determined by these bits. This effect enhances the acoustics of the fan being driven by the PWM3 output. Time Slot Increase Time for 33% to 100% 000 = 1 35 sec 001 = 2 17.6 sec 010 = 3 11.8 sec 011 = 5 7 sec 100 = 8 4.4 sec 101 = 12 3 sec 110 = 24 1.6 sec 111 = 48 0.8 sec When this bit is 1, acoustic enhancement is enabled on PWM3 output. These bits select the ramp rate applied to the PWM2 output. Instead of PWM2 jumping instantly to its newly calculated speed, PWM2 ramps gradually at the rate determined by these bits. This effect enhances the acoustics of the fans being driven by the PWM2 output. Time Slot Increase Time for 33% to 100% 000 = 1 35 sec 001 = 2 17.6 sec 010 = 3 11.8 sec 011 = 5 7 sec 100 = 8 4.4 sec 101 = 12 3 sec 110 = 24 1.6 sec When this bit is 1, acoustic enhancement is enabled on PWM2 output.
[3] [6:4]
EN3 ACOU2
R/W R/W
[7]
1
EN2
R/W
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 39. PWM Minimum Duty Cycle Registers
Register Address 0x64 0x65 0x66
1
R/W1 R/W R/W R/W
Description PWM1 minimum duty cycle. PWM2 minimum duty cycle. PWM3 minimum duty cycle.
Power-On Default 0x80 (50% duty cycle) 0x80 (50% duty cycle) 0x80 (50% duty cycle)
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. Register 0x64, Register 0x65, and Register 0x66--PWM Minimum Duty Cycle Registers (Power-On Default = 0x80, 50% duty cycle)
Bit <7:0> Name PWM duty cycle R/W R/W 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).
Table 41. TMIN Registers1
Register Address 0x67 0x68 0x69
1
R/W2 R/W R/W R/W
Description Remote 1 temperature TMIN. Local temperature TMIN. Remote 2 temperature TMIN.
Power-On Default 0x9A (90C) 0x9A (90C) 0x9A (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.
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ADT7473
Table 42. THERM Limit Registers1
Register Address 0x6A 0x6B 0x6C
1
R/W2 R/W R/W R/W
Description Remote 1 THERM limit. Local THERM limit. Remote 2 THERM limit.
Power-On Default 0xA4 (100C) 0xA4 (100C) 0xA4 (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 over temperature. It also ensures some level of cooling in the event that software or hardware locks up. If set to 0x80, this feature is disabled. The PWM output remains at 100% until the temperature drops below THERM Limit - Hysteresis. If the THERM pin is programmed as an output, then exceeding these limits by 0.25C can cause the THERM pin to assert low as an output. 2 These registers become read-only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to these registers have no effect.
Table 43. Temperature/TMIN Hysteresis Registers1
Register Address 0x6D Bit Name HYSL [3:0] R/W2 R/W Description Remote 1 and local temperature hysteresis. Local temperature hysteresis. 0C to 15C of hysteresis can be applied to the local temperature AFC and dynamic TMIN control loops. Remote 1 temperature hysteresis. 0C to 15C of hysteresis can be applied to the Remote 1 temperature AFC and dynamic TMIN control loops. Remote 2 temperature hysteresis. Local temperature hysteresis. 0C to 15C of hysteresis can be applied to the local temperature AFC and dynamic TMIN control loops. Power-On Default 0x44
HYSR1 [7:4]
0x6E HYSR2 [7:4]
R/W
0x40
1
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.
Table 44. XNOR Tree Test Enable Register
Register Address 0x6F Bit Name XEN [0] R/W1 R/W 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
Reserved [7:1]
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 1 Temperature Offset Register (0x70)
Bit [7:0] R/W1 R/W Description Allows a twos complement offset value to be automatically added to or subtracted from the Remote 1 temperature reading. This is to compensate for any inherent system offsets such as PCB trace resistance. LSB value = 0.5C. Power-On Default 0x00
1
This register becomes read only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.
Table 46. Local Temperature Offset Register (0x71)
Bit [7:0]
1
R/W1 R/W
Description Allows a twos complement offset value to be automatically added to or subtracted from the local temperature reading. LSB value = 0.5C.
Power-On Default 0x00
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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ADT7473
Table 47. Remote 2 Temperature Offset Register (0x72)
Bit [7:0] R/W1 R/W Description Allows a twos complement offset value to be automatically added to or subtracted from the Remote 2 temperature reading. This is to compensate for any inherent system offsets such as PCB trace resistance. LSB value = 0.5C. Power-On Default 0x00
1
This register becomes read only when the Configuration Register 1 lock bit is set to 1. Any further attempts to write to this register have no effect.
Table 48. Register 0x73--Configuration Register 2 (Power-On Default = 0x00)
Bit [0] [1] [2] [3] [4] [5] [6] Name FanPresenceDT Fan1 Detect Fan2 Detect Fan3 Detect AVG ATTN CONV R/W1 R/W Read Read Read R/W R/W R/W Description When FanPresenceDT = 1, the state of Bits [3:1] of Register 0x73 reflects the presence of a 4-wire fan on the appropriate TACH channel. Fan1 Detect = 1 indicates a 4-wire fan is connected to the PWM1 input. Fan1 Detect = 1 indicates a 4-wire fan is connected to the PWM2 input. Fan1 Detect = 1 indicates a 4-wire fan is connected to the PWM3 input. AVG = 1, averaging on the temperature and voltage measurements is turned off. This allows measurements on each channel to be made much faster. ATTN = 1, the ADT7473 removes the attenuators from the VCCP input. The VCCP input can be used for other functions such as connecting up external sensors. CONV = 1, the ADT7473 is put into a single-channel ADC conversion mode. In this mode, the ADT7473 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 Reserved. 001 VCCP. 010 VCC (3.3 V). 011 Reserved. 100 Reserved. 101 Remote 1 temperature. 110 Local temperature. 111 Remote 2 temperature. SHDN = 1, ADT7473 goes into shutdown mode. All PWM outputs assert low (or high depending on the state of the INV bit) to switch off all fans. The PWM current duty cycle registers read 0x00 to indicate the fans are not being driven.
[7]
SHDN
R/W
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 49. Register 0x74--Interrupt Mask Register 1 (Power-On Default = 0x00)
Bit [1] [2] [4] [5] [6] [7] Name VCCP VCC R1T LT R2T OOL R/W R/W R/W R/W R/W R/W R/W Description 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. 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, then 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 are still asserted. OOL = 1, then 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 are not asserted.
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ADT7473
Table 50. Register 0x75--Interrupt Mask Register 2 (Power-On Default <7:0> = 0x00)
Bit [1] [2] [3] [4] [5] [6] [7] Name OVT FAN1 FAN2 FAN3 F4P D1 D2 R/W Read only R/W R/W R/W R/W R/W R/W Description 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. F4P = 1, masks SMBALERT for a Fan 4 fault. If the TACH4 pin is being used as the THERM input, this bit masks SMBALERT for a THERM timer event. 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.
Table 51. Register 0x76--Extended Resolution 11
Bit [3:2] [5:4]
1
Name VCCP VCC
R/W Read-only Read-only
Description VCCP LSBs. Holds the 2 LSBs of the 10-bit VCCP measurement. VCC LSBs. Holds the 2 LSBs of the 10-bit VCC measurement.
If this register is read, this register and the registers holding the MSB of each reading are frozen until read.
Table 52. Register 0x77--Extended Resolution Register 21
Bit [3:2] [5:4] [7:6]
1
Name TDM1 LTMP TDM2
R/W Read-only Read-only Read-only
Description 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.
Table 53. Register 0x78--Configuration Register 3 (Power-On Default = 0x00)
Bit [0] [1] Name ALERT THERM R/W1 R/W R/W Description ALERT = 1, Pin 5 (PWM2/SMBALERT) is configured as an SMBALERT interrupt output to indicate out-oflimit error conditions. THERM Enable = 1 enables THERM functionality on Pin 9. Also determined by Bit 0 and Bit 1 (PIN9FUNC) of Configuration Register 4. Direction is controlled by Bit 5, Bit 6, and Bit 7 of Configuration Register 5 (0x7C). When THERM is asserted, if the fans are running and the boost bit is set, the fans run at full speed. THERM can also be programmed so that a timer monitors the duration THERM has been asserted. When THERM is an input and BOOST = 1, assertion of THERM causes all fans to run at the maximum programmed duty cycle for fail-safe cooling. FAST = 1, enables fast TACH measurements on all channels. This increases the TACH measurement rate from once per second to once every 250 ms (4 x). DC1 = 1, enables TACH measurements to be continuously made on TACH1. Fans must be driven by dc. Setting this bit prevents pulse stretching, because it is not required for DC-driven motors. DC2 = 1, enables TACH measurements to be continuously made on TACH2. Fans must be driven by dc. Setting this bit prevents pulse stretching, because it is not required for DC-driven motors. DC3 = 1, enables TACH measurements to be continuously made on TACH3. Fans must be driven by dc. 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. Fans must be driven by dc. Setting this bit prevents pulse stretching, because it is not required for DC-driven motors.
[2] [3] [4] [5] [6] [7]
1
BOOST FAST DC1 DC2 DC3 DC4
R/W R/W R/W R/W R/W R/W
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. A | Page 72 of 76
ADT7473
Table 54. Register 0x79--THERM Timer Status Register (Power-On Default = 0x00)
Bit [7:1] [0] Name TMR ASRT/ TMR0 R/W Read-only Read-only Description Times the duration THERM input is asserted. These seven bits read 0 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 seconds to be reported back with a resolution of 22.76 ms.
Table 55. Register 0x7A--THERM Timer Limit Register (Power-On Default = 0x00)
Bit [7:0] Name LIMT R/W R/W 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 seconds to be programmed. If the THERM assertion time exceeds this limit, Bit 5 (F4P) of Interrupt Status Register 2 (Reg. 0x42) is set. If the limit value is 0x00, an interrupt is generated immediately on the assertion of the THERM input.
Table 56. Register 0x7B--TACH Pulses per Revolution Register (Power-On Default = 0x55)
Bit [1:0] Name FAN1 R/W R/W 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
R/W
[5:4]
FAN3
R/W
[7:6]
FAN4
R/W
Rev. A | Page 73 of 76
ADT7473
Table 57. Register 0x7C--Configuration Register 5 (Power-On Default = 0x00)
Bit [0] Name TWOS COMPL TempOffset GPIOD GPIOP RES R1 THERM R/W1 R/W Description Twos complement = 1, sets the temperature range to twos complement temperature range. Twos complement = 0, changes the temperature range to Offset 64. When this bit is changed, the ADT7473 interprets all relevant temperature register values as defined by this bit. TempOffset = 0 sets offset range to 64C at 0.5C resolution. TempOffset = 1 sets offset range to 128C at 1C resolution. GPIO direction. When GPIO function is enabled, this determines whether the GPIO is an input (0) or an output (1). GPIO polarity. When the GPIO function is enabled and is programmed as an output, this bit determines whether the GPIO is active low (0) or high (1). Reserved R1 THERM = 1, THERM temperature limit functionality enabled for Remote 1 temperature channel; that is, THERM is bidirectional. R1 THERM = 0, THERM is a timer input only. THERM can also be disabled on any channel by * * [6] Local THERM R/W 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] [2] [3] [4] [5]
R/W
Local THERM = 1, THERM temperature limit functionality enabled for the local temperature channel; that is, THERM is bidirectional. Local THERM = 0, 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.
[7]
R2 THERM
R/W
R2 THERM = 1, THERM temperature limit functionality enabled for Remote 2 temperature channel; that is, THERM is bidirectional. R2 THERM = 0, 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
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 58. Register 0x7D--Configuration Register 4 (Power-On Default = 0x00)
Bit [1:0] Name Pin9FUNC R/W1 Read/write Description These bits set the functionality of Pin 9: 00 = TACH4 (default) 01 = THERM 10 = SMBALERT 11 = GPIO THERM Disable = 1, disables THERM over temperature feature. Max/Full on THERM = 0; when THERM temperature limit is exceeded, fans go to full speed. Max/Full on THERM = 1; when THERM temperature limit is exceeded, fans go to maximum programmed fan speed. Max/Full on THERM = 1; when THERM limit is exceeded, fans go to maximum speed as defined in Register 0x38, Register 0x39, Register 0x3A. Unused. Bypass VCCP attenuator. When set, the measurement scale for this channel changes from 0 V (0x00) to 2.2965 V (0xFF). Unused.
[2] [3]
THERM Disable Max/Full on THERM
Read/write Read/write
[4:5] [6] [7]
1
RES BpAttVCCP RES
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.
Rev. A | Page 74 of 76
ADT7473
Table 59. 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 60. 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. A | Page 75 of 76
ADT7473 OUTLINE DIMENSIONS
0.197 0.193 0.189
16
9
1
0.158 0.154 0.150
8
0.244 0.236 0.228
PIN 1 0.065 0.049 0.069 0.053 8 0
0.010 0.025 0.004 BSC COPLANARITY 0.004
0.012 0.008
SEATING PLANE
0.010 0.006
0.050 0.016
COMPLIANT TO JEDEC STANDARDS MO-137-AB
Figure 79. 16-Lead Shrink Small Outline Package [QSOP] (RQ-16) Dimensions shown in inches
ORDERING GUIDE
Model ADT7473ARQZT1 ADT7473ARQZ-REEL1 ADT7473ARQZ-REEL71 EVAL-ADT7473EB
P PT
Temperature Range -40C to +125C -40C to +125C -40C to +125C
Package Description 16-Lead QSOP 16-Lead QSOP 16-Lead QSOP Evaluation Board
Package Option RQ-16 RQ-16 RQ-16
1
TP PT
Z = Pb-free part.
(c)2006 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D04686-0-2/06(A)
T T
T T
Rev. A | Page 76 of 76

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