Analog Devices ADT7473 Manual

Dbcool 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 optimizes system acoustics

MIN

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® 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

PWM1

PWM2

PWM3

TACH1

TACH2

TACH3

TACH4

THERM

Rev. 0

Information furnished by Analog Devices is believed to be accurate and reliable.

However, no responsibility is assumed by Analog Devices for its use, nor for any

infringements of patents or other rights of third parties that may result from its use.

Specifications subject to change without notice. No license is granted by implication

or otherwise under any patent or patent rights of Analog Devices. Trademarks and

registered trademarks are the property of their respective owners.

FUNCTIONAL BLOCK DIAGRAM

ADT7473

PWM

REGISTERS

AND

ENHANCEMENT

CONTROLLERS

(HF AND LF)

PERFORMANCE

MONITORING

PROTECTION

TO ADT7473

D1+

D1–

SRC

CONDITIONING

D2+

D2–

MULTIPLEXER

CCP

BAND GAP

TEMP. SENSOR

dBCool

Monitor and Fan Controller

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 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 also

provides critical thermal protection to the system using the

bidirectional THERM pin as an output to prevent system or

component overheating.

SCL SDA SMBALERT

SERIAL BUS

INTERFACE

ACOUSTIC

AUTOMATIC

FAN SPEED

CONTROL

DYNAMIC

MIN

CONTROL

FAN

SPEED

COUNTER

THERMAL

INPUT

10-BIT

SIGNAL

ADC

AND

ANALOG

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

Remote Thermal

ADT7473

control mode

MIN

ADDRESS

POINTER

PWM

CONFIGURATION

REGISTERS

INTERRUPT

MASKING

INTERRUPT

STATUS

REGISTERS

LIMIT

COMPARATORS

VALUE AND

LIMIT

REGISTERS

www.analog.com

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Summary of Contents for Analog Devices ADT7473

Page 1 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.
Page 2: Table Of Contents
Typical Performance Characteristics ..........7 Power-On Default ..............31 Product Description................. 9 Programming the Automatic Fan Speed Control Loop .... 32 Comparison Between ADT7467 and ADT7473 ...... 9 Automatic Fan Control Overview..........32 Recommended Implementation..........9 Step 1: Hardware Configuration ..........33 Serial Bus Interface..............
Page 3: Specifications
ADT7473 SPECIFICATIONS to T to V , unless otherwise specified. All voltages are measured with respect to GND, unless otherwise specified. Typicals are at T = 25°C and represent most likely parametric norm. Logic inputs accept input high voltages up to V , even when device is operating down to V .
Page 4 ADT7473 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 ABSOLUTE MAXIMUM RATINGS Table 2. Stresses above those listed under Absolute Maximum Ratings Parameter Rating may cause permanent damage to the device. This is a stress Positive Supply Voltage (V 3.6 V rating only; functional operation of the device at these or any Voltage on Any Input or Output Pin −0.3 V to +3.6 V...
Page 6: Pin Configuration And Function Descriptions
Can be configured as a bidirectional THERM pin, which 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.
Page 7: Typical Performance Characteristics
ADT7473 TYPICAL PERFORMANCE CHARACTERISTICS D+ TO GND 100mV D+ TO V 60mV –20 40mV –40 –60 –10 100M 200M 300M 400M 500M 600M NOISE FREQUENCY (Hz) LEAKAGE RESISTANCE (MΩ) Figure 4. Remote Temperature Error vs. PCB Resistance Figure 7. Remote Temperature Error vs. Common-Mode Noise Frequency 1.20...
Page 8 Figure 12. Remote Temperature Error vs. Temperature Figure 10. Remote Temperature Error vs. Power Supply Noise Frequency –0.5 –1.0 –1.5 –40 –20 OIL BATH TEMPERATURE (°C) Figure 11. Internal Temperature Error vs. ADT7473 Temperature Rev. 0 | Page 8 of 76...
Page 9: Product Description
SMBALERT output to signal out-of-limit conditions. THERM COMPARISON BETWEEN ADT7467 AND ADT7473 SMBALERT The ADT7473 can only be powered via a 3.3 V supply, and does GPIO not support 5 V operation like the ADT7467. RECOMMENDED IMPLEMENTATION High frequency PWM drive can be independently selected for Configuring the ADT7473, as shown in Figure 13, allows the each PWM channel on the ADT7473.
Page 10: Serial Bus Interface
On PCs and servers, control of the ADT7473 is carried out In the ADT7473, write operations contain either one or two using the SMBus. The ADT7473 is connected to this bus as a bytes, and read operations contain one byte. To write data to...
Page 11: Write Operations
Figure 16. Reading Data from a Previously Selected Register It is possible to read a data byte from a data register without For the ADT7473, the send byte protocol is used to write a first writing to the address pointer register, if the address register address to RAM for a subsequent single-byte read from pointer register is already at the correct value.
Page 12: Read Operations
In the ADT7473, the receive byte protocol is used to read a ANALOG-TO-DIGITAL CONVERTER single byte of data from a register whose address has previously All analog inputs are multiplexed into the on-chip, successive been set by a send byte or write byte operation.
Page 13: Vccp Limit Registers
ADT7473 into single-channel ADC conversion mode. In this Table 5 shows the input ranges of the analog inputs and output mode, the ADT7473 can be made to read a single voltage codes of the 10-bit ADC. channel only. If the internal ADT7473 clock is used, the selected When the ADC is running, it samples and converts a voltage input is read every 711 μs.
Page 14: Temperature Measurement Method
The technique used in the ADT7473 is to measure the change is biased above ground by an internal diode at the D− input. C1 in V when the device is operated at three different currents.
Page 15 D– input and the base to the D+ input. Figure 23 and resolution of 0.25°C. However, this exceeds the operating Figure 24 show how to connect the ADT7473 to an NPN or temperature range of the device, so local temperature PNP transistor for temperature measurement.
Page 16: Series Resistance Cancellation
Parasitic resistance to the ADT7473 D+ and D− inputs (seen in HIGH , is 6 μA. If the ADT7473 current levels do not match series with the remote diode) is caused by a variety of factors the current levels specified by the CPU manufacturer, it including PCB track resistance and track length.
Page 17 0°C 0000 0000 00 by a linear, constant value. 10.25°C 0000 1010 01 The ADT7473 has temperature offset registers at addresses 0x70 25.5°C 0001 1001 10 and 0x72 for the Remote 1 and Remote 2 temperature channels. 50.75°C 0011 0010 11 By performing a one-time calibration of the system, the user 75°C...
Page 18: Additional Adc Functions For Temperature Measurement
Remote 1 Temperature It is important to note that the temperature can be read from Local Temperature the ADT7473 as an 8-bit value (with 1°C resolution) or as a Remote 2 Temperature 10-bit value (with 0.25°C resolution). If only 1°C resolution is required, the temperature readings can be read back at any time Configuration Register 2 (Reg.
Page 19: Limits, Status Registers, And Interrupts
Reg. 0x58 TACH3 Minimum Low Byte = 0xFF default 8-Bit Limits The following is a list of 8-bit limits on the ADT7473. Reg. 0x59 TACH3 Minimum High Byte = 0xFF default Voltage Limit Registers Reg. 0x5A TACH4 Minimum Low Byte = 0xFF default Reg.
Page 20: Status Registers
Bit 6 (D1) = 1, indicates an open or short on D1+/D1– inputs. monitoring cycle time for voltage and temperature monitoring with averaging disabled is 19 ms. The ADT7473 is a derivative Bit 5 (F4P) = 1, indicates Fan 4 has dropped below the of the ADT7467.
Page 21 STATUS BIT Assigning THERM Functionality to a Pin TEMP BACK IN LIMIT (STATUS BIT STAYS SET) Pin 9 on the ADT7473 has four possible functions: SMBus SMBALERT INTERRUPT ALERT, THERM , GPIO, and TACH4. The user chooses the MASK BIT SET...
Page 22: Therm Timer
ADT7473 When using the THERM timer, be aware of the following. The user can also set up the ADT7473 so that, when the THERM pin is driven low externally, the fans run at 100%. The After a THERM timer read (Reg. 0x79): fans run at 100% for the duration of the time the THERM pin is The contents of the timer are cleared on read.
Page 23 THERM output asserts. If the <22.76 ms in Hour 1, >182.08 ms in Hour 2, and >5.825 ADT7473 is not pulling THERM low, but THERM is sec in Hour 3, this can indicate that system performance is...
Page 24 ON READ F4P BIT (BIT 5) MASK REGISTER 2 (REG. 0x75) Figure 30. Functional Block Diagram of ADT7473’s THERM Monitoring Circuitry Configuring the THERM Pin as Bidirectional THERM LIMIT 0.25°C In addition to monitoring THERM as an input, the ADT7473 THERM LIMIT can optionally drive THERM low as an output.
Page 25: Fan Drive Using Pwm Control
Figure 34 shows a typical drive circuit for 4-wire fans. As the The ADT7473 PWM frequency can be set to a selection of low PWM input on 4-wire fans is usually internally pulled up to a frequencies or a single high PWM frequency.
Page 26 ADT7473 Driving up to Three Fans from PWM3 Signal conditioning in the ADT7473 accommodates the slow rise and fall times typical of fan tachometer outputs. The TACH measurements for fans are synchronized to particular maximum input signal range is 0 V to 3.6 V. In the event that...
Page 27 ADT7473 PULL-UP 4.7kΩ TYPICAL FAN SPEED COUNTER TACH TACH OUTPUT ADT7473 Figure 37. Fan with TACH Pull-Up to V PULL-UP 4.7kΩ TACH TYPICAL OUTPUT <1kΩ TACH FAN SPEED TACH FAN SPEED COUNTER COUNTER ZD1* TACH ADT7473 OUTPUT ADT7473 × *CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8 *SEE TEXT Figure 38.
Page 28 Reg. 0x2F TACH4 High Byte = 0x00 default Fan Speed (RPM) = (90,000 × 60)/Fan TACH Reading Reading Fan Speed from the ADT7473 The measurement of fan speeds involves a 2-register read for where: each measurement.
Page 29 0 = Logic high for 100% PWM duty cycle. Fan Spin-Up 1 = Logic low for 100% PWM duty cycle. The ADT7473 has a unique fan spin-up function. It spins PWM2 Configuration (Reg. 0x5D) the fan at 100% PWM duty cycle until two TACH pulses are detected on the TACH input.
Page 30: Fan Presence Detect
Control Loop section. Set bit 0 of Configuration Register 2 (0x73). In manual fan speed control mode, the ADT7473 allows the duty cycle of any PWM output to be manually adjusted. This Wait 5 ms. can be useful if the user wants to change fan speed in software or adjust PWM duty cycle output for test purposes.
Page 31: Xnor Tree Test Mode
(the system processor power rail is powered THERM monitoring is disabled. The THERM timer up), a fail-safe timer begins to count down. If the ADT7473 is should hold its value prior to the S3 or S5 state. not addressed by any valid SMBus transactions before the fail- safe timeout (4.6 sec) lapses, the ADT7473 drives the fans to full...
Page 32: Programming The Automatic Fan Speed Control Loop
PWM outputs. The three PWM outputs can be used to control up to four fans. The ADT7473 allows the speed AUTOMATIC FAN CONTROL OVERVIEW of four fans to be monitored. Each temperature channel has a...
Page 33: Step 1: Hardware Configuration
Decisions about how these capabilities are used should involve Is the CPU fan to be controlled using the ADT7473 or will the system thermal/mechanical engineer. Consider the it run at full speed 100% of the time?
Page 34 ADT7473 Recommended Implementation 1 • Configuring the ADT7473, as in Figure 46, provides the system CPU temperature measured using the Remote 1 designer with the following features: temperature channel. • • Two PWM outputs for fan control of up to three fans. (The Ambient temperature measured through the Remote 2 front and rear chassis fans are connected in parallel.)
Page 35: Step 2: Configuring The Mux
ADT7473 STEP 2: CONFIGURING THE MUX Automatic Fan Control Mux Options <7:5> (BHVR), Registers 0x5c, 0x5d, 0x5e. After the system hardware configuration is determined, the fans can be assigned to particular temperature channels. Not only 000 = Remote 1 temperature controls PWMx...
Page 36 <7:5> (BHVR), PWM1 Configuration Register 0x5c. 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 101 = Fastest speed calculated by local and Remote 2...
Page 37: Step 3: Tmin Settings For Thermal Calibration Channels
ADT7473 Registers STEP 3: T SETTINGS FOR THERMAL CALIBRATION CHANNELS Reg. 0x67, Remote 1 Temperature T = 0x9A (90°C) is the temperature at which the fans start to turn on under Reg. 0x68, Local Temperature T = 0x9A (90°C) automatic fan control. The speed at which the fan runs at T Reg.
Page 38: Step 4: Pwm Min For Each Pwm (Fan) Output
ADT7473 STEP 4: PWM FOR EACH PWM (FAN) OUTPUT Programming the PWM Registers The PWM registers are 8-bit registers that allow the is the minimum PWM duty cycle at which each fan in minimum PWM duty cycle for each output to be configured the system runs.
Page 39: Step 6: Trange For Temperature Channels
Can graphically program and visualize this functionality Reg. 0x38, PWM1 Maximum Duty Cycle = 0xFF (100% default) using the ADT7473 evaluation software. Ask your local Analog Devices representative for details. Reg. 0x39, PWM2 Maximum Duty Cycle = 0xFF (100% default)
Page 40 ADT7473 is implemented as a slope, which means that as PWM Example 3: Calculate T , given that T = 30°C, T RANGE RANGE is changed, T changes, but the actual slope remains the 40°C, and PWM = 33% duty cycle = 85 (decimal).
Page 41 Actual Fan Speed Profile RANGE This example uses the mux configuration, described in Step 2: Configuring the Mux, 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.
Page 42: Step 7: Ttherm For Temperature Channels
ADT7473 Note on 4-Wire Fans The control range for 4-wire fans is much wider than that of The fans remain running at 100% until the temperature drops 3-wire fans. In many cases, 4-wire fans can start with a PWM below T −...
Page 43: Step 8: Thyst For Temperature Channels
ADT7473 RANGE 100% THERM THERMAL CALIBRATION 100% CONFIG RAMP CONTROL PWM1 (ACOUSTIC GENERATOR ENHANCEMENT) TACHOMETER 1 RANGE TACH1 MEASUREMENT CPU FAN SINK THERMAL CALIBRATION CONFIG REMOTE 2 = 100% CPU TEMP RAMP CONTROL PWM2 (ACOUSTIC GENERATOR ENHANCEMENT) TACHOMETER 2 TACH2...
Page 44 ADT7473 RANGE 100% THERM THERMAL CALIBRATION 100% CONFIG RAMP CONTROL PWM1 (ACOUSTIC GENERATOR ENHANCEMENT) TACHOMETER 1 RANGE TACH1 MEASUREMENT CPU FAN SINK THERMAL CALIBRATION CONFIG REMOTE 2 = 100% CPU TEMP RAMP CONTROL PWM2 (ACOUSTIC GENERATOR ENHANCEMENT) TACHOMETER 2 TACH2...
Page 45: Dynamic Tmin Control Mode
In addition to the automatic fan speed control mode described VENTS POWER I/O CARDS POWER in the Automatic Fan Control Overview section, the ADT7473 SUPPLY SUPPLY has a mode that extends the basic automatic fan speed control loop. Dynamic T...
Page 46 This is important because instead of designing for the worst case, the system thermals can be defined as operating zones. ADT7473 can self- adjust its fan control loop to maintain either an operating zone temperature or a system target temperature. For example, one...
Page 47: Step 9: Operating Points For Temperature Channels
Operating Point Registers required to run as fast. The ADT7473 increases or decreases fan Reg. 0x33, Remote 1 Operating Point = 0xA4 (100°C default) speeds as necessary to maintain the operating point tempera- ture, allowing for system-to-system variation and removing the Reg.
Page 48: Step 10: High And Low Limits For Temperature Channels
STEP 10: HIGH AND LOW LIMITS FOR Short Cycle and Long Cycle TEMPERATURE CHANNELS The ADT7473 implements two loops: a short cycle and a long cycle. The short cycle takes place every n monitoring cycles. The low limit defines the temperature at which the T value The long cycle takes place every 2n monitoring cycles.
Page 49 ADT7473 Figure 66 shows the steps taken during the long cycle. Once the temperature exceeds the operating temperature minus the hysteresis (OP − Hyst), T starts to decrease. This occurs WAIT 2n during the short cycle (see Figure 65). The rate at which T...
Page 50: Step 11: Monitoring Therm
Intel Pentium 4 proces- sor. To do this, the PROCHOT output of the Pentium 4 is connected to the THERM input of the ADT7473. Rev. 0 | Page 50 of 76...
Page 51: Enhancing System Acoustics
PROCHOT output pulls the THERM temperature channel. The chosen T value is dynamically input low on the ADT7473. This gives the maximum adjusted based on the current temperature, operating point, and temperature at which the Pentium 4 can run before clock high and low limits for this zone.
Page 52 It also causes the system fans to fan-centric approach is how acoustic enhancement works on stay on longer than necessary because the fan’s reaction is the ADT7473. merely delayed. The user has no control over noise from Enabling Acoustic Enhancement for Each PWM Output different fans driven by the same temperature source.
Page 53: Step 12: Ramp Rate For Acoustic Enhancement
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 sec to reach 100% when a ramp rate of 1 time slot is selected.
Page 54 ADT7473 Figure 74 shows remote temperature plotted against PWM duty Figure 76 shows the PWM output response for a ramp rate of 2. cycle for enhanced acoustics mode. The ramp rate is set to 48, In this instance, the fan took about 17.6 sec to reach full which corresponds to the fastest ramp rate.
Page 55 Slower Ramp Rates 110 = 6.4 sec 111 = 3.2 sec The ADT7473 can be programmed for much longer ramp times by slowing the ramp rates. Each ramp rate can be slowed by a <6:4> ACOU2, selects the ramp rate for PWM2.
Page 56: Register Tables
ADT7473 REGISTER TABLES Table 15. ADT7473 Registers Address Description Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Default Lockable? 0x21 Reading 0x00 0x22 Reading 0x00 0x25 Remote 1 0x01 Temperature 0x26 Local...
Page 57 ADT7473 Address Description Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Default Lockable? 0x50 Local Temp Low 0x01 Limit 0x51 Local Temp High 0xFF Limit 0x52 Remote 2 Temp 0x01 Low Limit...
Page 58 If V Lo (Bit 1 of the Dynamic T Control Register 1, 0x36) is set, V can control the sleep state of the ADT7473. (Pin 3) is the supply voltage for the ADT7473. Rev. 0 | Page 58 of 76...
Page 59 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.) •...
Page 60 ADT7473 Table 21. Register 0x36—Dynamic T Control Register 1 (Power-On Default = 0x00) Name Description <0> CYR2 Read/write MSB of 3-Bit Remote 2 Cycle Value. The other two bits of the code reside in Dynamic T Control Register 2 (Reg. 0x37). These three bits define the delay time between making subsequent T adjustments in the control loop, in terms of the number of monitoring cycles.
Page 61 ADT7473 Table 22. Register 0x37—Dynamic T Control Register 2 (Power-On Default = 0x00) Name Description <2:0> CYR1 Read/write 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 62 (Lockable.) <2> Read-only 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. <3>...
Page 63 ADT7473 Table 27. Voltage Limit Registers Register Address Description Power-On Default 0x46 Read/write low limit. 0x00 0x47 Read/write high limit. 0xFF 0x48 Read/write low limit. 0x00 0x49 Read/write high limit. 0xFF Setting the Configuration Register 1 lock bit has no effect on these registers.
Page 64 ADT7473 Table 31. PWM Configuration Registers Register Address Description Power-On Default 0x5C Read/write PWM1 configuration. 0x82 0x5D Read/write PWM2 configuration. 0x82 0x5E Read/write PWM3 configuration. 0x82 Name Description <2:0> SPIN Read/write These bits control the startup timeout for PWMx. The PWM output stays high until two valid TACH rising edges are seen from the fan.
Page 65 ADT7473 Table 32. TEMP T /PWM Frequency Registers RANGE Register Address Description Power-On Default 0x5F Read/write Remote 1 T /PWM1 frequency. 0xCC RANGE 0x60 Read/write Local temperature T /PWM2 frequency. 0xCC RANGE 0x61 Read/write Remote 2 T /PWM3 frequency. 0xCC...
Page 66 SYNC = 0 synchronizes only TACH3 and TACH4 to PWM3 output. <5> Read/write 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 T – hysteresis value.
Page 67 0x00 = 0% duty cycle (fan off). 0x40 = 25% duty cycle. 0x80 = 50% duty cycle. 0xFF = 100% duty cycle (fan full speed). These registers become read-only when the ADT7473 is in automatic fan control mode. Table 36. T Registers Register Address...
Page 68 ADT7473 Table 37. THERM Limit Registers Register Address Description Power-On Default Remote 1 THERM limit. 0x6A Read/write 0xA4 (100°C) Local THERM limit. 0x6B Read/write 0xA4 (100°C) 0x6C Read/write Remote 2 THERM limit. 0xA4 (100°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.
Page 69 CONV Read/write 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>...
Page 70 ADT7473 Table 45. Register 0x75—Interrupt Mask Register 2 (Power-On Default <7:0> = 0x00) Name Description Read only OVT = 1, masks SMBALERT for overtemperature THERM conditions. FAN1 Read/write FAN1 = 1, masks SMBALERT for a Fan 1 fault. FAN2 Read/write FAN2 = 1, masks SMBALERT for a Fan 2 fault.
Page 71 ADT7473 Table 49. Register 0x79— THERM Timer Status Register (Power-On Default = 0x00) Name Description <7:1> Read-only Times the duration THERM input is asserted. These seven bits read 0 until the THERM assertion time exceeds 45.52 ms. <0> Read-only ASRT/ This bit is set high on the assertion of the THERM input, and is cleared on read.
Page 72 2sC = 1, sets the temperature range to twos complement temperature range. 2sC = 0, changes the temperature range to Offset 64. When this bit is changed, the ADT7473 interprets all relevant temperature register values as defined by this bit.
Page 73 ADT7473 Table 54. Register 0x7E—Manufacturer’s Test Register 1 (Power-On Default = 0x00) Name Description <7:0> Reserved Read-only Manufacturer’s test register. These bits are reserved for manufacturer’s test purposes and should not be written to under normal operation. Table 55. Register 0x7F—Manufacturer’s Test Register 2 (Power-On Default = 0x00)
Page 74: Outline Dimensions
ADT7473 OUTLINE DIMENSIONS 0.193 0.154 0.236 PIN 1 0.069 0.065 0.053 0.049 8° 0.010 0.025 0° 0.012 0.050 0.004 SEATING 0.010 0.008 0.016 PLANE COPLANARITY 0.006 0.004 COMPLIANT TO JEDEC STANDARDS MO-137-AB Figure 79. 16-Lead Shrink Small Outline Package [QSOP]...
Page 75 ADT7473 NOTES Rev. 0 | Page 75 of 76...

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