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FEATURES
Monitors up to 5 voltages
Controls and monitors up to 4 fans
High and low frequency fan drive signal
1 on-chip and 2 remote temperature sensors
Extended temperature measurement range up to 191°C
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
www.BDTIC.com/ADI
VID4/GPIO4
VID3/GPIO3
VID2/GPIO2
VID1/GPIO1
VID0/GPIO0
GPIO6
PWM1
PWM2
PWM3
TACH1
TACH2
TACH3
TACH4
THERM
+5V
+12V
+2.5V
Rev. B
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
VID5
PWM
REGISTERS
AND
CONTROLLERS
(HF AND LF)
PERFORMANCE
V
TO ADT7476
CC
V
CC
D1+
D1–
D2+
D2–
CONDITIONING
IN
MULTIPLEXER
IN
IN
V
CCP
BAND GAP
TEMP. SENSOR
Controller and Voltage Monitor
GENERAL DESCRIPTION
The ADT7476 dBCool® controller is a thermal monitor
and multiple PWM fan controller for noise-sensitive or power-
sensitive applications requiring active system cooling. The
ADT7476 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. The effectiveness of the system's thermal
solution can be monitored using the THERM input. The
ADT7476 also provides critical thermal protection to the
system using the bidirectional THERM pin as an output to
prevent system or component overheating.
ADDR
ADDREN
SELECT
SCL SDA SMBALERT
SMBus
VID/GPIO
ADDRESS
REGISTER
SELECTION
AUTOMATIC
FAN SPEED
CONTROL
FAN
SPEED
COUNTER
MONITORING
THERMAL
PROTECTION
ACOUSTIC
ENHANCEMENT
CONTROL
INPUT
SIGNAL
10-BIT
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
dBCool Remote Thermal
ADT7476
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.
ADT7476
www.analog.com
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Summary of Contents for Analog Devices dBCool ADT7476
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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
ADT7476 TABLE OF CONTENTS Features ....................1 Temperature Measurement Method ........20 General Description ................. 1 Factors Affecting Diode Accuracy........... 22 Functional Block Diagram .............. 1 Additional ADC Functions for Temperature Measurement 23 Revision History ................3 Limits, Status Registers, and Interrupts........25 Specifications.................. -
Page 3: Revision History
ADT7476 REVISION HISTORY 10/07—Rev. A to Rev. B Changes to Register 0x76 and Register 0x77 in Table 18...53 Changes to Bit 3 in Table 26............58 Changes to Table 29 Register Address..........59 Changes to Bit 1 in Table 51............68 3/06—Rev. 0 to Rev. A Changes to Features Section ............1 Changes to Table 1 ................4 Inserted Table 3..................6... -
Page 4: Specifications
ADT7476 SPECIFICATIONS to T to V , unless otherwise noted. Table 1. Parameter Unit Test Conditions/Comments POWER SUPPLY Supply Voltage Supply Current, I Interface inactive, ADC active TEMPERATURE-TO-DIGITAL CONVERTER Local Sensor Accuracy ±0.5 ±1.5 °C 0°C ≤ T ≤ 85°C ±2.5 °C –40°C ≤... -
Page 5: Timing Diagram
ADT7476 Parameter Unit Test Conditions/Comments 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 Input Low Voltage, V DIGITAL INPUT CURRENT Input High Current, I ±1 μA Input Low Current, I... -
Page 6: Absolute Maximum Ratings
ADT7476 ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE Table 2. Parameter Rating θ is specified for the worst-case conditions, that is, a device Positive Supply Voltage (V 3.6 V soldered in a circuit board for surface-mount packages. Maximum Voltage on +12V 16 V Table 3. -
Page 7: Pin Configuration And Function Descriptions
ADT7476 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS PWM1/XTO +2.5V /THERM +12V /VID5 VID0/GPIO0 ADT7476 TOP VIEW VID1/GPIO1 VID4/GPIO4 (Not to Scale) VID2/GPIO2 VID3/GPIO3 D1– TACH3 PWM2/SMBALERT D2– TACH4/THERM/SMBALERT/GPIO6/ADDR SELECT TACH1 TACH2 PWM3/ADDREN Figure 3. Pin Configuration Table 4. Pin Function Descriptions Pin No. - Page 8 ADT7476 Pin No. Mnemonic Description D1– Cathode Connection to First Thermal Diode. Anode Connection to First Thermal Diode. VID4 Digital Input. Voltage supply readouts from CPU. This value is read into the VID code register (0x43). GPIO4 General-Purpose Open-Drain Digital I/O. Analog Input.
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Page 9: Typical Performance Characteristics
ADT7476 TYPICAL PERFORMANCE CHARACTERISTICS –10 –20 –30 100mV 60mV –40 40mV –50 –60 –10 100M 200M 300M 400M 500M 600M CAPACITANCE (nF) NOISE FREQUENCY (Hz) Figure 4. Temperature Error vs. Capacitance Between D+ and D− Figure 7. Remote Temperature Error vs. Differential Mode Noise Frequency 1.20 1.18 1.16... - Page 10 ADT7476 250mV –2 100mV –4 –6 –0.5 –8 –1.0 –10 –1.5 –12 –2.0 100M 200M 300M 400M 500M 600M –40 –20 OIL BATH TEMPERATURE (°C) FREQUENCY (Hz) Figure 10. Remote Temperature Error vs. Power Supply Noise Frequency Figure 12. Remote Temperature Error vs. Temperature www.BDTIC.com/ADI –0.5 –1.0...
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Page 11: Product Description
ADT7476 PRODUCT DESCRIPTION • For the ADT7476, acoustic filtering is now assigned to The ADT7476 is a complete thermal monitor and multiple fan temperature zones and not to fans. Smoothing times have controller for any system requiring thermal monitoring and been increased for better acoustic performance. -
Page 12: Recommended Implementation
ADT7476 • RECOMMENDED IMPLEMENTATION Remote temperature zone measured through Remote 2 temperature channel. Configuring the ADT7476, as shown in Figure 13, allows the • Local temperature zone measured through the internal system designer to use the following features: temperature channel. •... -
Page 13: Serial Bus Interface
ADT7476 SERIAL BUS INTERFACE ADT7476 Control of the ADT7476 is carried out using the serial system 10kΩ management bus (SMBus). The ADT7476 is connected to this ADDR SELECT bus as a slave device, under the control of a master controller. PWM3/ADDREN The ADT7476 has a 7-bit serial bus address. - Page 14 ADT7476 When all data bytes have been read or written, stop On PCs and servers, control of the ADT7476 is carried out conditions are established. In write mode, the master pulls using the SMBus. The ADT7476 is connected to this bus as a the data line high during the 10th clock pulse to assert a slave device, under the control of a master controller, which is stop condition.
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Page 15: Write Operations
ADT7476 START BY ACK. BY ACK. BY STOP BY ADT7476 MASTER ADT7476 MASTER FRAME 1 FRAME 2 SERIAL BUS ADDRESS BYTE ADDRESS POINTER REGISTER BYTE Figure 19. Writing to the Address Pointer Register Only START BY ACK. BY NO ACK. BY STOP BY MASTER ADT7476... -
Page 16: Read Operations
ADT7476 Write Byte Alert Response Address In this operation, the master device sends a command byte Alert response address (ARA) is a feature of SMBus devices that and one data byte to the slave device, as follows: allows an interrupting device to identify itself to the host when multiple devices exist on the same bus. -
Page 17: Voltage Measurement Input
ADT7476 VOLTAGE MEASUREMENT INPUT VOLTAGE LIMIT REGISTERS The ADT7476 has four external voltage measurement channels. Associated with each voltage measurement channel is a high It can also measure its own supply voltage, V . Pin 20 to Pin 23 and low limit register. Exceeding the programmed high or low can measure 5 V, 12 V, and 2.5 V supplies and the processor limit causes the appropriate status bit to be set. - Page 18 ADT7476 Configuration Register 2 (0x73) Table 6. Conversion Time with Averaging Disabled Channel Measurement Time (ms) Bit 4 = 1, averaging off. Voltage Channels Bit 5 = 1, bypass input attenuators. Remote Temperature 1 Bit 6 = 1, single-channel convert mode. Remote Temperature 2 Local Temperature TACH1 Minimum High Byte Register (0x55)
- Page 19 ADT7476 Table 9. 10-Bit ADC Output Code vs. V Input Voltage ADC Output 12 V (3.3 V 2.5 V Decimal Binary (10 Bits) <0.0156 <0.0065 <0.0042 <0.0032 <0.00293 00000000 00 0.0156 to 0.0312 0.0065 to 0.0130 0.0042 to 0.0085 0.0032 to 0.0065 0.0293 to 0.0058 00000000 01 0.0312 to 0.0469...
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Page 20: Vid Code Monitoring
ADT7476 VID CODE MONITORING detected and reported back by the ADT7476. Bit 0 of Interrupt Status Register 2 (0x42) is the 12 V/VC bit and denotes a VID The ADT7476 has five dedicated voltage ID (VID code) inputs. change when set. The VID code change bit is set when the logic These are digital inputs that can be read back through the VID states on the VID inputs are different than they were 11 μs register (0x43) to determine the processor voltage required or... - Page 21 ADT7476 value of V varies from device to device and individual give a temperature output in 10-bit, twos complement format. calibration is required to null this out, so the technique is To further reduce the effects of noise, digital filtering is unsuitable for mass production.
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Page 22: Factors Affecting Diode Accuracy
ADT7476 FACTORS AFFECTING DIODE ACCURACY Transistors, such as 2N3904, 2N3906, or equivalents in SOT-23 packages, are suitable devices to use. Remote Sensing Diode The ADT7476 is designed to work with either substrate Table 10. Twos Complement Temperature Data Format transistors built into processors or with discrete transistors. Temperature Digital Output (10-Bit) Substrate transistors are generally PNP types with the collector... -
Page 23: Additional Adc Functions For Temperature Measurement
ADT7476 Changing Bit 1 of Configuration Register 5 (0x7C) changes the Register 0x4E, Remote 1 Temperature Low Limit = 0x81 default resolution and therefore the range of the temperature offset as Register 0x4F, Remote 1 Temperature High Limit = 0x7F default either having a range of –63°C to +127°C with a resolution of Register 0x50, Local Temperature Low Limit = 0x81 default 1°C or having a range of −63°C to +64°C with a resolution of... - Page 24 ADT7476 The fans run at this speed until the temperature drops below Single-Channel ADC Conversions THERM minus hysteresis. This can be disabled by setting the Setting Bit 6 of Configuration Register 2 (0x73) places the BOOST bit in Configuration Register 3, Bit 2 (Register 0x78). ADT7476 into single-channel ADC conversion mode.
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Page 25: Limits, Status Registers, And Interrupts
ADT7476 LIMITS, STATUS REGISTERS, AND INTERRUPTS 16-Bit Limits LIMIT VALUES The fan TACH measurements are 16-bit results. The fan TACH Associated with each measurement channel on the ADT7476 limits are also 16 bits, consisting of a high byte and low byte. are high and low limits. -
Page 26: Status Registers
ADT7476 For applications in which the monitoring cycle time is important, Interrupt Status Register 1 (0x41) it can be calculated easily. Bit 7 (OOL) = 1, denotes that a bit in Status Register 2 is set and Status Register 2 should be read. The total number of channels measured is •... - Page 27 ADT7476 HIGH LIMIT HIGH LIMIT TEMPERATURE TEMPERATURE CLEARED ON READ (TEMP BELOW LIMIT) STICKY CLEARED ON READ STATUS BIT (TEMP BELOW LIMIT) STICKY STATUS BIT TEMP BACK IN LIMIT (STATUS BIT STAYS SET) TEMP BACK IN LIMIT SMBALERT (STATUS BIT STAYS SET) Figure 29.
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Page 28: Therm Timer
ADT7476 Enabling the SMBALERT Interrupt Output If the temperature is below T or if the duty cycle in manual mode is set to Register 0x00, pulling the THERM low externally The SMBALERT interrupt function is disabled by default. has no effect. See Figure 31 for more information. Pin 10 or Pin 14 can be reconfigured as an SMBALERT output to signal out-of-limit conditions. - Page 29 ADT7476 Bit 0 of the THERM timer is set to 1 because a THERM THERM assertion is occurring. The THERM timer increments from zero. THERM 0 0 0 0 0 0 1 TIMER 7 6 5 3 2 1 0 If the THERM timer limit (Reg.
- Page 30 ADT7476 Configuring the Relevant THERM Behavior Alternatively, OS- or BIOS-level software can timestamp when the system is powered on. If an SMBALERT is gen- Configure the desired pin as the THERM timer input. erated due to the THERM timer limit being exceeded, Setting Bit 1 ( THERM timer enable) of Configuration another timestamp can be taken.
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Page 31: Fan Drive Using Pwm Control
ADT7476 Enabling and Disabling THERM on Individual Channels server fans, the MOSFET must handle the higher current requirements. The only other stipulation is that the MOSFET THERM can be enabled/disabled for individual or combina- should have a gate voltage drive, V <... - Page 32 ADT7476 Figure 37 shows a typical drive circuit for 4-wire fans. Because the MOSFET can handle up to 3.5 A, it is simply a matter of connecting another fan directly in parallel with the 12V 12V first. Care should be taken in designing drive circuits with 12V, 4-WIRE FAN 10kΩ...
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Page 33: Laying Out 3-Wire Fans
ADT7476 LAYING OUT 3-WIRE FANS Figure 40 shows how to lay out a common circuit arrangement PULL-UP for 3-wire fans. 4.7kΩ TACH TYPICAL OUTPUT TACH FAN SPEED 12V OR 5V COUNTER ZD1* ADT7476 1N4148 3.3V OR 5V *CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8 × V Figure 42. - Page 34 ADT7476 The fan counter does not count the fan TACH output pulses Because the device is essentially measuring the fan TACH directly because the fan speed could be less than 1000 RPM and period, the higher the count value, the slower the fan is actually it takes several seconds to accumulate a reasonably large and running.
- Page 35 ADT7476 Calculating Fan Speed Fan Start-up Timeout Assuming a fan with two pulses per revolution and the To prevent the generation of false interrupts as a fan spins up, ADT7476 programmed to measure two pulses per revolution, because it is below running speed, the ADT7476 includes a fan fan speed is calculated by start-up timeout function.
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Page 36: Programming Trange
ADT7476 PWM1, PWM 2, PWM3 Frequency Registers (0x5F to 0x61) from 0% to 100% in steps of 0.39%. The value to be programmed into the PWM register is given by Bits [2:0] FREQ. 000 = 11.0 Hz Value (decimal) = PWM /0.39 001 = 14.7 Hz Example 1: For a PWM duty cycle of 50%... -
Page 37: Programming The Automatic Fan Speed Control Loop
ADT7476 PROGRAMMING THE AUTOMATIC FAN SPEED CONTROL LOOP To understand the automatic fan speed control loop, use the The ADT7476 has a local temperature sensor and two remote ADT7476 evaluation board and software while reading this temperature channels that can be connected to a CPU on-chip section. -
Page 38: Step 1: Hardware Configuration
ADT7476 THERMAL CALIBRATION 100% CONFIG RAMP CONTROL PWM1 GENERATOR (ACOUSTIC ENHANCEMENT) TACHOMETER 1 REMOTE 1 RANGE TACH1 MEASUREMENT TEMP THERMAL CALIBRATION 100% CONFIG RAMP CONTROL PWM2 (ACOUSTIC GENERATOR ENHANCEMENT) TACHOMETER 2 TACH2 MEASUREMENT LOCAL RANGE TEMP THERMAL CALIBRATION CONFIG 100% RAMP CONTROL PWM3... - Page 39 ADT7476 THERMAL CALIBRATION 100% CONFIG RAMP CONTROL PWM1 GENERATOR (ACOUSTIC ENHANCEMENT) TACHOMETER 1 RANGE TACH1 MEASUREMENT REMOTE 1 = CPU FAN SINK THERMAL CALIBRATION 100% AMBIENT TEMP CONFIG RAMP CONTROL PWM2 GENERATOR (ACOUSTIC ENHANCEMENT) TACHOMETER 2 TACH2 MEASUREMENT RANGE LOCAL = THERMAL CALIBRATION CONFIG VRM TEMP...
- Page 40 ADT7476 ADT7476 FRONT CHASSIS TACH2 PWM1 TACH1 CPU FAN PWM3 5(VRM9)/6(VRM10) REAR VID[0:4]/VID[0.5] CHASSIS TACH3 D2– THERM PROCHOT AMBIENT TEMPERATURE D1– +12V /VID5 SMBALERT Figure 49. Recommended Implementation 1 www.BDTIC.com/ADI • VRM temperature using local temperature sensor. Recommended Implementation 2 •...
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Page 41: Step 2: Configuring The Mux
ADT7476 ADT7476 FRONT CHASSIS TACH2 PWM1 PWM2 TACH1 CPU FAN PWM3 5(VRM9)/6(VRM10) REAR VID[0:4]/VID[0.5] CHASSIS TACH3 D2– THERM PROCHOT AMBIENT TEMPERATURE D1– +12V /VID5 Figure 50. Recommended Implementation 2 www.BDTIC.com/ADI STEP 2: CONFIGURING THE MUX 010 = Remote 2 temperature controls PWMx 101 = Fastest speed calculated by local and Remote 2 After the system hardware configuration is determined, the fans temperature controls PWMx... - Page 42 ADT7476 THERMAL CALIBRATION 100% CONFIG RAMP CONTROL PWM1 GENERATOR (ACOUSTIC ENHANCEMENT) TACHOMETER 1 RANGE TACH1 MEASUREMENT REMOTE 1 = CPU FAN SINK THERMAL CALIBRATION AMBIENT TEMP 100% CONFIG RAMP CONTROL GENERATOR (ACOUSTIC PWM2 ENHANCEMENT) TACHOMETER 2 TACH2 MEASUREMENT RANGE LOCAL = THERMAL CALIBRATION CONFIG VRM TEMP...
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Page 43: Step 3: Tmin Settings For Thermal Calibration Channels
ADT7476 THERMAL CALIBRATION 100% CONFIG RAMP CONTROL PWM1 GENERATOR (ACOUSTIC ENHANCEMENT) TACHOMETER 1 RANGE TACH1 MEASUREMENT CPU FAN SINK THERMAL CALIBRATION REMOTE 2 = 100% CPU TEMP CONFIG RAMP CONTROL PWM2 GENERATOR (ACOUSTIC ENHANCEMENT) TACHOMETER 2 TACH2 MEASUREMENT RANGE LOCAL = THERMAL CALIBRATION VRM TEMP CONFIG... -
Page 44: Step 4: Pwm Min For Each Pwm (Fan) Output
ADT7476 100% THERMAL CALIBRATION 100% CONFIG RAMP CONTROL PWM1 GENERATOR (ACOUSTIC ENHANCEMENT) TACHOMETER 1 RANGE TACH1 MEASUREMENT CPU FAN SINK THERMAL CALIBRATION REMOTE 2 = 100% CPU TEMP CONFIG RAMP CONTROL PWM2 GENERATOR (ACOUSTIC ENHANCEMENT) TACHOMETER 2 TACH2 MEASUREMENT RANGE LOCAL = THERMAL CALIBRATION VRM TEMP... -
Page 45: Step 5: Pwm Max For Pwm (Fan) Outputs
ADT7476 Programming the PWM Registers 100% The PWM registers are 8-bit registers that allow the mini- mum 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 PWM register is given by... -
Page 46: Step 6: Trange For Temperature Channels
Ask your local The T value can be selected for each temperature channel: RANGE Analog Devices, Inc. representative for details. Remote 1, local, and Remote 2 temperature. Bits [7:4] (T RANGE of Register 0x5F to Register 0x61 define the T... - Page 47 ADT7476 2°C Table 17. Selecting a T Value RANGE 2.5°C Bits [7:4] (°C) 3.33°C RANGE 4°C 0000 5°C 0001 6.67°C 0010 3.33 8°C 10°C 0011 13.3°C 0100 16°C 0101 6.67 20°C 0110 26.6°C 32°C 0111 40°C 1000 13.33 53.3°C 1001 80°C 1010 TEMPERATURE ABOVE T...
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Page 48: For Temperature Channels
ADT7476 2°C VRM TEMPERATURE 2.5°C 3.33°C 4°C 5°C 6.67°C CPU TEMPERATURE 8°C 10°C 13.3°C AMBIENT TEMPERATURE 16°C 20°C 26.6°C 32°C 40°C 53.3°C 80°C TEMPERATURE ABOVE T TEMPERATURE ABOVE T 2°C VRM TEMPERATURE 2.5°C 3.33°C 4°C 5°C CPU TEMPERATURE 6.67°C 8°C AMBIENT TEMPERATURE 10°C 13.3°C... - Page 49 ADT7476 The T limit should be considered the maximum worst-case example, setting hysteresis on the Remote 1 channel also sets THERM the hysteresis on Remote 1 THERM . operating temperature of the system. Because exceeding any limit runs all fans at 100%, it has very negative acoustic Hysteresis Registers THERM effects.
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Page 50: Step 8: Thyst For Temperature Channels
ADT7476 In some applications, it is required that fans not turn off below STEP 8: T FOR TEMPERATURE CHANNELS HYST but remain running at PWM . Bits [7:5] of Enhanced is the amount of extra cooling a fan provides after the HYST Acoustics Register 1 (0x62) allow the fans to be turned off or to temperature measured has dropped back below T... -
Page 51: Fan Presence Detect
ADT7476 Enhanced Acoustics Register 1 (0x62) 010 = 12.5 seconds 011 = 7.5 seconds Bit 7 MIN3 = 0, PWM3 is off (0% PWM duty cycle) when 100 = 4.7 seconds temperature is below T − T HYST 101 = 3.1 seconds Bit 7 MIN3 = 1, PWM3 runs at PWM3 minimum duty cycle 110 = 1.6 seconds below T... -
Page 52: Fan Sync
OR’ e d PWMs. This VID4 OR’ e d PWM can in turn be used to drive a chassis fan. See the Analog Devices website, located at www.analog.com, for TACH1 information about the Fan sync function. -
Page 53: Register Tables
ADT7476 REGISTER TABLES Table 18. ADT7476 Registers Address R/W Description Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Default Lockable 0x10 R/W Configuration Extra MasterEn SlaveEn THERM in SLOW SLOW SLOW Remote 1 0x00 Register 6 Slow Remote 2... - Page 54 ADT7476 Address R/W Description Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Default Lockable 0x42 R/W Interrupt Status F4P/GPIO6 FAN3 FAN2 FAN1 12 V/VC 0x00 Register 2 FAULT FAULT 0x43 R/W VID Code VIDSEL THLD VID5...
- Page 55 ADT7476 Address R/W Description Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Default Lockable 0x63 R/W Enhanced ACOU2 ACOU2 ACOU2 ACOU3 ACOU3 ACOU3 0x00 Acoustics Reg. 0x64 R/W PWM1 Min 0x80 Duty Cycle 0x65 R/W PWM2 Min 0x80...
- Page 56 ADT7476 Address R/W Description Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Default Lockable 0x7D R/W Configuration BpAtt BpAtt BpAtt V BpAtt Max/Speed THERM Pin14Func Pin14Func 0x00 Register 4 12 V 2.5 V on THERM Disable 0x7E...
- Page 57 ADT7476 1, 2, 3 Table 22. Temperature Reading Registers (Power-On Default = 0x80) Register Address Description 0x25 Read-only Remote 1 temperature reading (8 MSBs of reading). 0x26 Read-only Local temperature reading (8 MSBs of reading). 0x27 Read-only Remote 2 temperature reading (8 MSBs of reading). If the extended resolution bits of these readings are also being read, the extended resolution registers (0x76, 0x77) must be read first.
- Page 58 ADT7476 Table 26. Register 0x40—Configuration Register 1 (Power-On Default = 0x04) Name Description 1, 2 STRT Logic 1 enables monitoring and PWM control outputs based on the limit settings programmed. Logic 0 disables monitoring and PWM control based on the default power-up limit settings. Note that the limit values programmed are preserved even if a Logic 0 is written to this bit and the default settings are enabled.
- Page 59 ADT7476 Table 28. Register 0x42—Interrupt Status Register 2 (Power-On Default = 0x00) Name Description 12 V/VC Read-only A 1 indicates that the 12 V high or low limit has been exceeded. This bit is cleared on a read of the status register only if the error condition has subsided.
- Page 60 ADT7476 Table 30. Voltage Limit Registers Register Address Description Power-On Default 0x44 2.5 V low limit 0x00 0x45 2.5 V high limit 0xFF 0x46 low limit 0x00 0x47 high limit 0xFF 0x48 low limit 0x00 0x49 high limit 0xFF 0x4A 5 V low limit 0x00 0x4B...
- Page 61 ADT7476 Table 33. Register 0x55—TACH1 Minimum High Byte (Power-On Default = 0xFF) Bits Name Description [4:0] Reserved Read-only 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. [7:5] SCADC When Bit 6 of Configuration Register 2 (0x73) is set (single-channel ADC mode), these bits are used to...
- Page 62 ADT7476 Table 36. TEMP T /PWM Frequency Registers RANGE Register Address Description Power-On Default 0x5F Remote 1 T /PWM1 frequency 0xC4 RANGE 0x60 Local T /PWM2 frequency 0xC4 RANGE 0x61 Remote 2 T /PWM3 frequency 0xC4 RANGE These registers become read-only when the Configuration Register 1 LOCK bit is set. Any subsequent attempts to write to these registers fail. Table 37.
- Page 63 ADT7476 Table 38. Register 0x62—Enhanced Acoustics Register 1 (Power-On Default = 0x00) Name Description [2:0] ACOU Assuming that PWMx is associated with the Remote 1 temperature channel, these bits define the maximum rate of change of the PWMx output for Remote 1 temperature-related changes. Instead of the fan speed jumping instantaneously to its newly determined speed, it ramps gradually at the rate determined by these bits.
- Page 64 ADT7476 Table 39. Register 0x63—Enhanced Acoustics Register 2 (Power-On Default = 0x00) Name Description [2:0] ACOU3 Assuming that PWMx is associated with the Local temperature channel, these bits define the maximum rate of change of the PWMx output for local temperature-related changes. Instead of the fan speed jumping instantaneously to its newly determined speed, it ramps gradually at the rate determined by these bits.
- Page 65 ADT7476 Table 40. PWMx Minimum Duty Cycle Registers Register Address Description Power-On Default 0x64 PWM1 minimum duty cycle 0x80 (50% duty cycle) 0x65 PWM2 minimum duty cycle 0x80 (50% duty cycle) 0x66 PWM3 minimum duty cycle 0x80 (50% duty cycle) These registers become read-only when the ADT7476 is in automatic fan control mode.
- Page 66 ADT7476 Table 43. THERM Limit Registers Register Address Description Power-On Default 0x6A Remote 1 THERM temperature limit 0x64 (100°C) 0x6B Local THERM temperature limit 0x64 (100°C) 0x6C Remote 2 THERM temperature limit 0x64 (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 67 ADT7476 Table 47. Local Temperature Offset Register Address Description Power-On Default 0x71 [7:0] Local temperature offset. 0x00 Allows a temperature offset to be applied automatically to the local temperature measurement. Bit 1 of Configuration Register 5 (0x7C) determines the range and resolution of this register.
- Page 68 ADT7476 Table 50. Register 0x74—Interrupt Mask Register 1 (Power-On Default = 0x00) Name Description 2.5 V/ THERM 2.5 V/ THERM = 1, masks SMBALERT for out-of-limit conditions on the 2.5 V/ THERM channel. timer = 1, masks SMBALERT for out-of-limit conditions on the V channel.
- Page 69 ADT7476 Table 54. Register 0x78—Configuration Register 3 (Power-On Default = 0x00) Name Description ALERT Enable ALERT = 1, Pin 10 (PWM2/SMBALERT) is configured as an SMBALERT interrupt output to indicate out-of-limit error conditions. ALERT = 0, Pin 10 (PWM2/SMBALERT) is configured as the PWM2 output. THERM/2.5 V THERM = 1 enables THERM functionality on Pin 22 and Pin 14, if Pin 14 is configured as THERM, determined by Bits 0 and 1 (Pin14Func) of Configuration Register 4.
- Page 70 ADT7476 Table 57. Register 0x7B—TACH Pulses per Revolution Register (Power-On Default = 0x55) Name Description [1:0] FAN1 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)
- Page 71 ADT7476 Name Description Local Local THERM = 1 , THERM temperature limit functionality enabled for local temperature channel; that THERM is, THERM is bidirectional. Local THERM = 0, THERM is a timer input only. Output only THERM can also be disabled on any channel by: In Offset 64 mode, writing −64°C to the appropriate THERM temperature limit.
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Page 72: Outline Dimensions
–40°C to +125°C 24-Lead QSOP RQ-24 EVAL-ADT7476EBZ 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. D05382-0-10/07(B) Rev. B | Page 72 of 72...
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