Analog Devices ADT7473 Manual
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Analog Devices ADT7473 Manual

Analog Devices ADT7473 Manual

Db cool remote thermal monitor and fan controller
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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 191°C
Dynamic T
control mode intelligently optimizes system
MIN
acoustics
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 Pentium 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
TACH1
TACH2
TACH3
TACH4
*THERM_LATCH
Rev. C
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.

FUNCTIONAL BLOCK DIAGRAM

ADT7473/ADT7473-1
PWM
PWM1
REGISTERS
PWM2
AND
CONTROLLERS
PWM3
(HF AND LF)
V
TO ADT7473/ADT7473-1
CC
V
CC
D1+
D1–
SRC
D2+
D2–
V
CCP
BAND GAP
TEMP SENSOR
*PIN FUNCTION ONLY AVAILABLE ON THE ADT7473-1
dBCool Remote Thermal Monitor

GENERAL DESCRIPTION

The ADT7473/ADT7473-1 dBCool® controller is a thermal
monitor and multiple PWM fan controller for noise sensitive
or power sensitive applications requiring active system cooling.
The ADT7473/ADT7473-1 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 T
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/
ADT7473-1 also provide critical thermal protection to the
system using the bidirectional THERM pin as an output to
prevent system or component overheating.
*ADDREN
*ADDR SELECT
SCL
SMBus
ADDRESS
SELECTION
ACOUSTIC
AUTOMATIC
ENHANCEMENT
FAN SPEED
CONTROL
CONTROL
DYNAMIC
T
MIN
CONTROL
FAN
SPEED
COUNTER
PERFORMANCE
MONITORING
THERMAL
PROTECTION
INPUT
10-BIT
SIGNAL
ADC
CONDITIONING
AND
ANALOG
MULTIPLEXER
BAND GAP
REFERENCE
GND
Figure 1.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.461.3113
and Fan Controller
ADT7473/ADT7473-1
MIN
SDA SMBALERT
SERIAL BUS
INTERFACE
ADDRESS
POINTER
REGISTER
PWM
CONFIGURATION
REGISTERS
INTERRUPT
MASKING
INTERRUPT
STATUS
REGISTERS
LIMIT
COMPARATORS
VALUE AND
LIMIT
REGISTERS
©2005–2007 Analog Devices, Inc. All rights reserved.
control mode
www.analog.com

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Summary of Contents for Analog Devices ADT7473

  • Page 1: Features

    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 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

  • Page 2: Table Of Contents

    Changes to Interrupt Mask Register 1 (0x74) Section....22 Changes to Table 61................ 71 Changes to Fan Drive Using PWM Control ....... 26 Changes to Reading Fan Speed from the ADT7473....28 6/07—Rev. A to Rev. B Changes to Ordering Guide ............76 Added ADT7473-1 .............Universal...

  • Page 3: Specifications

    OPEN-DRAIN SERIAL DATA BUS OUTPUT (SDA) Output Low Voltage, V = −4.0 mA High Level Output Current, I μA DIGITAL OUTPUT LOGIC LEVELS, ADT7473-1 (THERM_LATCH) ADTL+ Output High Voltage, V 0.75 × V Output Low Voltage, V SMBus DIGITAL INPUTS (SCL, SDA)

  • Page 4: Timing Diagram

    ADT7473/ADT7473-1 Parameter Unit Test Conditions/Comments DIGITAL INPUT LOGIC LEVELS (TACH INPUTS) Input High Voltage, V Maximum input voltage Input Low Voltage, V −0.3 Minimum input voltage Hysteresis V p-p DIGITAL INPUT LOGIC LEVELS (THERM) ADTL+ Input High Voltage, V 0.75 × V...

  • Page 5: Absolute Maximum Ratings

    ADT7473/ADT7473-1 ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE Table 2. θ is specified for the worst-case conditions, that is, a device Parameter Rating soldered in a circuit board for surface-mount packages. Positive Supply Voltage (V 3.6 V Voltage on Any Input or Output Pin −0.3 V to +3.6 V...

  • Page 6: Pin Configurations And Function Descriptions

    Digital I/O (Open Drain). Pulse-width modulated output to control the speed of Fan 3 and Fan 4. Requires 10 kΩ typical pull-up. Can be configured as a high or low frequency drive. ADDREN If pulled low on power-up, the ADT7473-1 enters address select mode, and the state of Pin 4 (ADDR SELECT) determines the ADT7473-1 slave address. TACH4 Digital Input (Open Drain).

  • Page 7: Typical Performance Characteristics

    ADT7473/ADT7473-1 TYPICAL PERFORMANCE CHARACTERISTICS D+ TO GND 100mV D+ TO V 60mV –20 40mV –40 –60 –10 100M 200M 300M 400M 500M 600M LEAKAGE RESISTANCE (MΩ) NOISE FREQUENCY (Hz) Figure 5. Remote Temperature Error vs. PCB Resistance Figure 8. Remote Temperature Error vs. Common-Mode Noise Frequency 1.20...
  • Page 8 ADT7473/ADT7473-1 250mV –2 100mV –4 –6 –0.5 –8 –1.0 –10 –1.5 –12 –2.0 100M 200M 300M 400M 500M 600M –40 –20 FREQUENCY (Hz) OIL BATH TEMPERATURE (°C) Figure 11. Remote Temperature Error vs. Power Supply Noise Frequency Figure 13. Remote Temperature Error vs. Temperature –0.5...

  • Page 9: Product Description

    SMBALERT output to signal out-of-limit individually on each temperature channel. This is not conditions. available on the ADT7467. Table 5 illustrates the differences between the ADT7473 and the • Bit 7 of Configuration Register 1 is no longer supported ADT7473-1.

  • Page 10: Serial Bus Interface

    (but not necessarily) the ICH. ADDRESS = 0x2E The ADT7473 has a fixed 7-bit serial bus address of 0101110 or Figure 15. Default SMBus Address = 0x2E 0x2E. The read/write bit must be added to get the 8-bit address (01011100 or 0x5C).
  • Page 11 AN UNEXPECTED ADDRESS. an address that is stored in the address pointer register. If data is NOTE THAT IF THE ADT7473-1 IS PLACED INTO ADDR SELECT written to the device, the write operation contains a second data MODE, PINS 8 AND 4 CANNOT BE USED AS THE ALTERNATIVE...

  • Page 12: Write Operations

    However, it is For the ADT7473/ADT7473-1, the send byte protocol is used to not possible to write data to a register without writing to the write a register address to RAM for a subsequent single-byte read address pointer register, because the first data byte of a write from the same address.

  • Page 13: Read Operations

    The ADT7473/ADT7473-1 uses the following SMBus read The ADT7473/ADT7473-1 includes an SMBus timeout protocols. feature. If there is no SMBus activity for 35 ms, the ADT7473/ ADT7473-1 assumes the bus is locked and releases the bus. Receive Byte This prevents the device from locking or holding the SMBus This operation is useful when repeatedly reading a single expecting data.

  • Page 14: Additional Adc Functions For Voltage Measurements

    ADT7473/ADT7473-1 into single-channel ADC conversion When the ADC is running, it samples and converts a voltage mode. In this mode, the ADT7473/ADT7473-1 can be made to input in 711 μs and averages 16 conversions to reduce noise; a read a single voltage channel only. If the internal ADT7473/ measurement takes nominally 11.38 ms.

  • Page 15: Temperature Measurement Method

    V , which varies Local Temperature Measurement from device to device. The ADT7473/ADT7473-1 contains an on-chip band gap The technique used in the ADT7473/ADT7473-1 measures temperature sensor whose output is digitized by the on-chip the change in V when the device is operated at three different 10-bit ADC.
  • Page 16 0000 1010 01 tion is required to null this out, so the technique is unsuitable 25.5°C 0001 1001 10 for mass production. The technique used in the ADT7473/ 50.75°C 0011 0010 11 ADT7473-1 is to measure the change in V when the device 75°C...

  • Page 17: Series Resistance Cancellation

    D– input and the emitter is connected The ADT7473/ADT7473-1 has a major advantage over other to the D+ input. If an NPN transistor is used, the emitter is devices for eliminating the effects of noise on the external connected to the D–...
  • Page 18 (−64°C to +191°C), the fault condi- offset register. tion is represented by −64°C = 0000 0000. If a discrete transistor is used with the ADT7473/ADT7473-1, Temperature Measurement Registers the best accuracy is obtained by choosing devices according to...

  • Page 19: Additional Adc Functions For Temperature Measurement

    ADDITIONAL ADC FUNCTIONS FOR TEMPERATURE MEASUREMENT TACH1 Minimum High Byte Register (0x55) A number of other functions are available on the ADT7473/ Bits [7:5] select the ADC channel for single-channel convert mode. ADT7473-1 to offer the system designer increased flexibility.

  • Page 20: Limits, Status Registers, And Interrupts

    Out-of-Limit Comparisons Associated with each measurement channel on the ADT7473/ ADT7473-1 are high and low limits. These can form the basis of Once all limits have been programmed, the ADT7473/ system status monitoring; a status bit can be set for any out-of- ADT7473-1 can be enabled for monitoring.

  • Page 21: Changes To Interrupt Status Register 2 (0X42) Section

    Interrupt Status Register 2 when this bit HIGH LIMIT is set. Alternatively, Pin 5 or Pin 9 on the ADT7473 can be config- ured as an SMBALERT output, while only Pin 9 can be configured TEMPERATURE to be an SMBALERT on the ADT7473-1.

  • Page 22: Changes To Interrupt Mask Register 1 (0X74) Section

    Register 0x75, Interrupt Mask Register 2 Channel D2, and Bit 0 in Status Register 2 is cleared. By default on the ADT7473-1, the THERM limit is set as 136°C for Remote These registers allow individual interrupt sources to be masked Channel 2 and 100°C for Remote Channel 1.

  • Page 23: Therm Timer

    Figure 34. Understanding the THERM Timer connected to the output of a trip point temperature sensor. Generating SMBALERT Interrupts from THERM Timer The timer is started on the assertion of the ADT7473/ Events ADT7473-1 THERM input and stopped when THERM is deasserted.
  • Page 24 INTERRUPT STATUS SMBALERT REGISTER 2 LATCH RESET CLEARED 1 = MASK ON READ F4P BIT (BIT 5) INTERRUPT MASK REGISTER 2 (REGISTER 0x75) Figure 35. Functional Block Diagram of the ADT7473 THERM Monitoring Circuitry Rev. C | Page 24 of 72...

  • Page 25: Fan Drive Using Pwm Control

    In all cases, the TACH signal from the fan must be kept below 3.6 V maximum to prevent damaging the ADT7473/ MONITORING ADT7473-1. If uncertain as to whether the fan used has an CYCLE open-collector or totem pole TACH output, use one of the Figure 36.

  • Page 26: Changes To Fan Drive Using Pwm Control

    PWM3 NDT3055L Driving Two Fans from PWM3 The ADT7473/ADT7473-1 has four TACH inputs available for Figure 41. Interfacing Two Fans in Parallel to the PWM3 Output Using a Single N-Channel MOSFET fan speed measurement, but only three PWM drive outputs. If a...
  • Page 27 ADT7473/ The fan tachometer readings are 16-bit values consisting of a ADT7473-1 2-byte read from the ADT7473/ADT7473-1. *CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8 × V Register 0x28, TACH1 Low Byte = 0x00 default Figure 44. Fan with Strong TACH Pull-Up to > V...

  • Page 28: Changes To Reading Fan Speed From The Adt7473

    Fan Spin-Up Register 0x5A, TACH4 Minimum Low Byte = 0xFF default The ADT7473/ADT7473-1 has a unique fan spin-up function. It spins the fan at 100% PWM duty cycle until two TACH pulses Register 0x5B, TACH4 Minimum High Byte = 0xFF default are detected on the TACH input.

  • Page 29: Changes To High Frequency Mode Pwm Drive Section

    During this time, the PWM Frequency Registers (Register 0x5F to Register 0x61) ADT7473/ADT7473-1 looks for two TACH pulses. If two TACH pulses are not detected, an interrupt is generated. Using Bits [2:0] FREQ Configuration Register 1 (0x40), Bit 5 (FSPDIS), this function- 000 = 11.0 Hz...

  • Page 30: Fan Presence Detect

    As the detection time only takes 5 ms, programming the PWM outputs to 100% and then back to their normal speed is not The ADT7473/ADT7473-1 includes an XNOR tree test mode. noticeable in most cases. This mode is useful for in-circuit test equipment at board-level testing.

  • Page 31: Power-On Default

    START FAIL-SAFE TIMER If V 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 fail- HAS THE ADT7473/ADT7473-1 BEEN ACCESSED BY A VALID safe timeout (4.6 seconds) lapses, the ADT7473 drives the fans...

  • Page 32: Programming The Automatic Fan Speed Control Loop

    PWM outputs. The three PWM AUTOMATIC FAN CONTROL OVERVIEW outputs can be used to control up to four fans. The ADT7473/ ADT7473-1 allows the speed of four fans to be monitored. Each The ADT7473/ADT7473-1 can automatically control the speed of fans based on the measured temperature.

  • Page 33: Step 1: Hardware Configuration

    Is the CPU fan to be controlled using the ADT7473/ the system thermal/mechanical engineer. Consider the ADT7473-1 or will it run at full speed 100% of the time? following questions: If run at full speed, 100% of the time, this frees up a PWM What ADT7473/ADT7473-1 functionality will be used? output, but the system is louder.
  • Page 34 ADT7473/ADT7473-1 • CPU temperature measured using the Remote 1 Recommended Implementation 1 temperature channel. Configuring the ADT7473, as in Figure 51, provides the system • Ambient temperature measured through the Remote 2 designer with the following features: temperature channel. •...

  • Page 35: Step 2: Configuring The Mux

    Bits [7:5] (BHVR), Register 0x5C, Register 0x5D, Register 0x5E. PWM3 outputs. The values selected for these bits determine how the mux connects a temperature measurement channel 011 = PWMx runs full speed (default for ADT7473-1) to a PWM output. 100 = PWMx disabled (default for ADT7473)
  • Page 36 This is an example of how to configure the mux in a system Example Mux Settings using the ADT7473/ADT7473-1 to control three fans. The CPU fan sink is controlled by PWM1, the front chassis fan is con- Bits [7:5] (BHVR), PWM1 Configuration Register (0x5C)

  • Page 37: Step 3: Tmin Settings For Thermal Calibration Channels

    ADT7473/ADT7473-1 STEP 3: T SETTINGS FOR THERMAL Registers CALIBRATION CHANNELS Register 0x67, Remote 1 Temperature T = 0x9A (90°C) is the temperature at which the fans start to turn on under Register 0x68, Local Temperature T = 0x9A (90°C) automatic fan control. The speed at which the fan runs at T Register 0x69, Remote 2 Temperature T = 0x9A (90°C)

  • Page 38: Step 4: Pwm Min For Each Pwm (Fan) Output

    ADT7473/ADT7473-1 STEP 4: PWM FOR EACH PWM (FAN) OUTPUT Example 1 is the minimum PWM duty cycle at which each fan in For a minimum PWM duty cycle of 50% the system runs. It is also the start speed for each fan under Value (decimal) = 50/0.39 = 128 (decimal)

  • Page 39: Step 6: Trange For Temperature Channels

    Value (decimal) = 50/0.39 = 128 (decimal) Graphically program and visualize this functionality using Value = 128 (decimal) or 80 (hex) the ADT7473/ADT7473-1 evaluation software. Ask your Example 2 local Analog Devices, Inc. representative for details. Figure 59 shows how adjusting PWM...
  • Page 40 ADT7473/ADT7473-1 For a given T value, the temperature at which the fan runs RANGE Table 17. Selecting a T Value RANGE at full speed for different PWM values can be easily Bits [7:4] (°C) RANGE calculated as follows: 0000 + (Max DC − Min DC) × T...
  • Page 41 = 40°C for VRM temperature RANGE This example uses the mux configuration described in the Step 2: Configuring the Mux section, with the ADT7473/ ADT7473-1 connected as shown in Figure 63. Both CPU TEMPERATURE ABOVE T temperature and VRM temperature drive the CPU fan connected to PWM1.

  • Page 42: Step 7: Ttherm For Temperature Channels

    ADT7473/ADT7473-1 STEP 7: T FOR TEMPERATURE CHANNELS the fan reaches full speed) by setting to that limit (for THERM THERM example, 70°C). is the absolute maximum temperature allowed on a THERM THERM Registers temperature channel. When operating above this temperature, a...

  • Page 43: Step 8: Thyst For Temperature Channels

    ADT7473/ADT7473-1 STEP 8: T FOR TEMPERATURE CHANNELS Hysteresis Registers HYST Register 0x6D, Remote 1, Local Hysteresis Register is the amount of extra cooling a fan provides after the HYST temperature measured has dropped back below T before the Bits [7:4], Remote 1 temperature hysteresis (4°C default) fan turns off.

  • Page 44: Dynamic Tmin Control Mode

    In addition to the automatic fan speed control mode described Figure 66. Chassis Airflow Issues in the Automatic Fan Control Overview section, the ADT7473/ ADT7473-1 has a mode that extends the basic automatic fan Worst-Case Processor Power Consumption speed control loop. Dynamic T...
  • Page 45 T control loop. because, instead of designing for the worst case, the system thermals can be defined as operating zones. The ADT7473/ ADT7473-1 can self-adjust its fan control loop to maintain either an operating zone temperature or a system target temperature.

  • Page 46: Step 9: Operating Points For Temperature Channels

    These 8-bit registers allow the operating required to run as fast. The ADT7473/ADT7473-1 increases or point temperatures to be programmed with 1°C resolution. decreases fan speeds as necessary to maintain the operating...

  • Page 47: Step 10: High And Low Limits For Temperature Channels

    This has the net effect of reducing the fan speed, allowing the system The ADT7473/ADT7473-1 implements two loops: a short cycle to get hotter. An interrupt can be generated when the tempera- and a long cycle.
  • Page 48 ADT7473/ADT7473-1 Figure 71 shows the steps taken during the long cycle. decreases depends on the programmed value of n. It also depends on how much the temperature has increased between WAIT 2n this monitoring cycle and the last monitoring cycle; that is, if...

  • Page 49: Step 11: Monitoring Therm

    To do this, the PROCHOT output of the Pentium 4 is • cannot exceed the high temperature limit. connected to the THERM input of the ADT7473/ADT7473-1. • If the temperature is below T , the fan is switched off or...

  • Page 50: Enhancing System Acoustics

    For psycho-acoustic PHTR2 = 0, ignores any THERM assertions. The Remote 2 reasons, the ADT7473/ADT7473-1 can prevent the PWM operating point register reflects its programmed value. output from reacting instantaneously to temperature changes.
  • Page 51 Remote 1 temperature. The fan-centric the values 1, 2, 3, 5, 8, 12, 24, and 48. The ramp rates are discrete approach is how acoustic enhancement works on the ADT7473/ time slots. For example, if the ramp rate is 8, then eight time slots ADT7473-1.

  • Page 52: Step 12: Ramp Rate For Acoustic Enhancement

    PWM output to ramp up from 0% to 100% duty READ TEMPERATURE cycle for an instantaneous change in temperature. This can be tested by putting the ADT7473/ADT7473-1 into manual mode CALCULATE and changing the PWM output from 0% to 100% PWM duty NEW PWM DUTY CYCLE cycle.
  • Page 53 Slower Ramp Rates PWM DUTY CYCLE (%) The ADT7473/ADT7473-1 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.

  • Page 54: Changes To Table 20

    ADT7473/ADT7473-1 REGISTER TABLES Table 20. ADT7473/ADT7473-1 Registers Default (ADT7473/ Lock- Addr. Description Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 ADT7473-1) able? 0x21 Reading 0x00 0x22 Reading 0x00 0x25 Remote 1 0x01...
  • Page 55 ADT7473/ADT7473-1 Default (ADT7473/ Lock- Addr. Description Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 ADT7473-1) able? 0x49 High Limit 0xFF 0x4E Remote 1 Temp. 0x01 Low Limit 0x4F Remote 1 Temp. 0xFF...
  • Page 56 ADT7473/ADT7473-1 Default (ADT7473/ Lock- Addr. Description Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 ADT7473-1) able? 0x6C Remote 2 THERM 0xA4/0xC8 Temp. Limit 0x6D Remote 1 and HYSR1 HYSR1 HYSR1 HYSR1 HYSL...
  • Page 57 Failed (internal circuitry destroyed). • Not populated. (The ADT7473/ADT7473-1 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.) •...
  • Page 58 ADT7473/ADT7473-1 1, , 2 3 Table 25. Operating Point Registers (Power-On Default = 0xA4) Register Address Description 0x33 Remote 1 operating point register (default = 100°C). 0x34 Local temperature operating point register (default = 100°C). 0x35 Remote 2 operating point register (default = 100°C).
  • Page 59 ADT7473/ADT7473-1 Table 27. Register 0x37—Dynamic T Control Register 2 (Power-On Default = 0x00) Name Description [2:0] CYR1 3-bit remote 1 cycle value. These three bits define the delay time between making subsequent T 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.
  • Page 60 This prevents rogue programs, such as viruses, from modifying critical system limit settings. (This is a lockable bit.) Read-only This bit is set to 1 by the ADT7473/ADT7473-1 to indicate only that the device is fully powered up and ready to begin system monitoring. FSPD When set to 1, this bit runs all fans at maximum speed as programmed in the maximum PWM duty cycle registers (0x30, 0x38, 0x39 and 0x3A ).
  • Page 61 Read-only Reserved on the ADT7473. THERM Limit Latch On the ADT7473-1, Therm Limit Latch = 1 indicates Remote Channel 2 latch. This is a THERM limit condition. Read-only 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 –...
  • Page 62 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 37. Register 0x5C, Register 0x5D, and Register 0x5E—Configuration Registers (ADT7473 Power-On Default = 0x82, ADT7473-1 Power-On Default = 0x62) Name...
  • Page 63 001 = Local temperature controls PWMx (automatic fan control mode). 010 = Remote 2 temperature controls PWMx (automatic fan control mode). 011 = PWMx runs full speed (default for ADT7473-1). 100 = PWMx disabled (default for ADT7473). 101 = Fastest speed calculated by local and Remote 2 temperature controls PWMx.
  • Page 64 SYNC = 0 synchronizes only TACH3 and TACH4 to PWM3 output. MIN1 When the ADT7473/ADT7473-1 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 T –...
  • Page 65 ADT7473/ADT7473-1 Table 41. Register 0x63—Enhanced Acoustics Register 2 (Power-On Default = 0x00) Name Description [2:0] ACOU3 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.
  • Page 66 0x6C Remote 2 THERM limit. ADT7473: 0xA4 (100°C) ADT7473-1: 0xC8 (136°C) If any temperature measured exceeds its THERM limit, all PWM outputs drive their fans at 100% duty cycle. This is a fail-safe mechanism incorporated to cool the system in the event of a critical overtemperature. It also ensures some level of cooling in the event that software or hardware locks up. If set to 0x80, this feature is disabled.

  • Page 67: Changes To Table 51

    CONV CONV = 1, the ADT7473/ADT7473-1 is put into a single-channel ADC conversion mode. In this mode, the ADT7473/ADT7473-1 can be made to read continuously from one input only, for example, Remote 1 temperature.
  • Page 68 ADT7473/ADT7473-1 Table 52. Register 0x74—Interrupt Mask Register 1 (Power-On Default = 0x00) Name Description = 1, masks SMBALERT for out-of-limit conditions on the V channel. = 1, masks SMBALERT for out-of-limit conditions on the V channel. R1T = 1, masks SMBALERT for out-of-limit conditions on the Remote 1 temperature channel.
  • Page 69 ALERT = 0 (default), ADT7473 Pin 5 is configured as PWM2. Enable ALERT = 1, Pin 5 for ADT7473 (PWM2/SMBALERT) is configured as an SMBALERT interrupt output to indicate out-of-limit error conditions. ALERT = 0 (default), ADT7473-1 Pin 5 is configured as THERM_LATCH .
  • Page 70 COMPL Twos complement = 0, changes the temperature range to Offset 64. When this bit is changed, the ADT7473/ADT7473-1 interprets all relevant temperature register values as defined by this bit. TempOffset TempOffset = 0 sets offset range to ±64°C at 0.5°C resolution.

  • Page 71: Changes To Table 61

    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 on ADT7473 On the ADT7473-1: THERM_LATCH Configuration...

  • Page 72: Outline Dimensions

    −40°C to +125°C 16-Lead QSOP RQ-16 EVAL-ADT7473EBZ Evaluation Board Z = RoHS Compliant Part. ©2005–2007 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D04686-0-8/07(C) Rev. C | Page 72 of 72...

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