adt7476a

Manufacturer Part Numberadt7476a
DescriptionDbcool Remote Thermal Controller And Voltage Monitor
ManufacturerAnalog Devices, Inc.
adt7476a datasheet
 
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FEATURES
Monitors up to five voltages
Improved TACH and PWM performance
Controls and monitors up to four fans
High and low frequency fan drive signal
One on-chip and two remote temperature sensors
Extended temperature measurement range up to 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
5 V support on all TACH and PWM channels
Meets SMBus 2.0 electrical specifications
VID5/GPIO5
VID4/GPIO4
VID3/GPIO3
VID2/GPIO2
VID1/GPIO1
VID0/GPIO0
GPIO6
PWM1
PWM2
PWM3
TACH1
TACH2
TACH3
TACH4
THERM
V
V
CC
D1+
D1–
D2+
D2–
+5V
IN
+12V
IN
+2.5V
IN
V
CCP
Rev. 0
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
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
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
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.
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.
Trademarks and registered trademarks are the property of their respective owners.
Controller and Voltage Monitor
GENERAL DESCRIPTION
The ADT7476A dBCOOL controller is a thermal monitor
and multiple PWM fan controller for noise-sensitive or power-
sensitive applications requiring active system cooling. The
ADT7476A can drive a fan using either a low or high frequency
drive signal and can monitor the temperature of up to two
remote sensor diodes plus its own internal temperature. The
part also measures and controls the speed of up to four fans, so
the fans operate at the lowest possible speed for minimum
acoustic noise.
The automatic fan speed control loop optimizes fan speed
for a given temperature. The effectiveness of the system’s
thermal solution can be monitored using the THERM input.
The ADT7476A also provides critical thermal protection to
the system using the bidirectional THERM pin as an output
to prevent system or component overheating.
FUNCTIONAL BLOCK DIAGRAM
ADDR
ADDREN
SELECT
SMBus
VID/GPIO
ADDRESS
REGISTER
SELECTION
PWM
REGISTERS
AUTOMATIC
AND
FAN SPEED
CONTROLLERS
CONTROL
(HF AND LF)
FAN
SPEED
COUNTER
PERFORMANCE
MONITORING
THERMAL
PROTECTION
TO ADT7476A
CC
ACOUSTIC
ENHANCEMENT
CONTROL
INPUT
SIGNAL
10-BIT
CONDITIONING
ADC
AND
ANALOG
MULTIPLEXER
BAND GAP
REFERENCE
BAND GAP
TEMP. SENSOR
GND
Figure 1.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Tel: 781.329.4700
Fax: 781.461.3113
Fax: 781.461.3113
dBCool
Remote Thermal
ADT7476A
SCL SDA SMBALERT
ADT7476A
SERIAL BUS
INTERFACE
ADDRESS
POINTER
REGISTER
PWM
CONFIGURATION
REGISTERS
INTERRUPT
MASKING
INTERRUPT
STATUS
REGISTERS
LIMIT
COMPARATORS
VALUE AND
LIMIT
REGISTERS
www.analog.com
www.analog.com
©2006 Analog Devices, Inc. All rights reserved.
©2006 Analog Devices, Inc. All rights reserved.

adt7476a Summary of contents

  • Page 1

    ... PWM fan controller for noise-sensitive or power- sensitive applications requiring active system cooling. The ADT7476A can drive a fan using either a low or high frequency drive signal and can monitor the temperature two remote sensor diodes plus its own internal temperature. The ...

  • Page 2

    ... Revision History ............................................................................... 2 Specifications..................................................................................... 3 Absolute Maximum Ratings............................................................ 5 Thermal Characteristics .............................................................. 5 ESD Caution.................................................................................. 5 Pin Configuration and Function Descriptions............................. 6 Typical Performance Characteristics ............................................. 8 Product Description....................................................................... 10 Feature Comparisons Between ADT7476A and ADT7468.. 10 Recommended Implementation............................................... 10 Serial Bus Interface..................................................................... 11 Write Operations ........................................................................ 14 Read Operations ......................................................................... 14 SMBus Timeout .......................................................................... 15 Virus Protection.......................................................................... 15 Voltage Measurement Input...................................................... 15 Analog-to-Digital Converter ...

  • Page 3

    ... V 0.1 20 μA 0.4 V 0.1 1.0 μA 2.0 V 0.4 V 500 mV Rev Page ADT7476A Test Conditions/Comments Interface inactive, ADC active 0°C ≤ T ≤ 85°C A –40°C ≤ T ≤ 125°C A 0°C ≤ T ≤ 85°C A –40°C ≤ T ≤ 125°C A High level Low level For 12 V channel ...

  • Page 4

    ... ADT7476A Parameter DIGITAL INPUT LOGIC LEVELS (TACH INPUTS) Input High Voltage Input Low Voltage Hysteresis DIGITAL INPUT LOGIC LEVELS (THERM) ADTL+ Input High Voltage Input Low Voltage DIGITAL INPUT CURRENT Input High Current Input Low Current, I ...

  • Page 5

    ... JA is specified for the worst-case conditions, that is, a device −65°C to +150°C soldered in a circuit board for surface-mount packages. 220°C Table 3. Thermal Resistance 260°C Package Type 300°C 24-lead QSOP 1500 V Rev Page ADT7476A θ θ Unit JA JC 122 31.25 °C/W ...

  • Page 6

    ... 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 ADT7476A enters address select mode, and the state of Pin 14 (ADDR SELECT) determines the ADT7476A’s slave address. 14 TACH4/ Digital Input (Open Drain) ...

  • Page 7

    ... Analog Input. Monitors processor core voltage ( V). CCP 24 PWM1/ Digital Output (Open Drain). Pulse width modulated output to control the speed of Fan 1. Requires 10 kΩ typical pull-up. XTO Also functions as the output from the XOR tree in XOR test mode. Rev Page ADT7476A ...

  • Page 8

    ... ADT7476A TYPICAL PERFORMANCE CHARACTERISTICS 0 –10 –20 –30 –40 –50 – CAPACITANCE (nF) Figure 4. Temperature Error vs. Capacitance Between D+ and D− GND –10 –20 –30 – LEAKAGE RESISTANCE (MΩ) Figure 5. Remote Temperature Error vs. PCB Resistance ...

  • Page 9

    ... Figure 10. Remote Temperature Error vs. Power Supply Noise Frequency 3.0 2.5 2.0 1.5 1.0 0.5 0 –0.5 –1.0 –1.5 –40 – OIL BATH TEMPERATURE (°C) Figure 11. Internal Temperature Error vs. ADT7476A Temperature 3.0 2.5 2.0 1.5 1.0 0.5 0 –0.5 –1.0 –1.5 –2.0 500M 600M Figure 12. Remote Temperature Error vs. ADT7476A Temperature 85 105 125 Rev Page ADT7476A – ...

  • Page 10

    ... ADT7476A PRODUCT DESCRIPTION The ADT7476A is a complete thermal monitor and multiple fan controller for any system requiring thermal monitoring and cooling. The device communicates with the system via a serial system management bus. The serial bus controller has a serial data line for reading and writing addresses and data (Pin 1), and an input line for the serial clock (Pin 2) ...

  • Page 11

    ... Pin 13 (PWM3/ ADDREN ) high, the ADT7476A has a default SMBus address of 0101110 or 0x2E. The read/write bit must be added to get the 8-bit address. If more than one ADT7476A used in a system, each ADT7476A is placed in ADDR SELECT mode by strapping Pin 13 low on power-up. The logic state of Pin 14 then determines the device’ ...

  • Page 12

    ... This is done by performing a write to the ADT7476A as before, but only the data byte containing the register address is sent, because no data is written to the register (see Figure 19). ...

  • Page 13

    ... MASTER FRAME 1 SERIAL BUS ADDRESS BYTE In addition to supporting the send byte and receive byte protocols, the ADT7476A also supports the read byte protocol. See Intel’s System Management Bus Specifications Rev. 2 for more information. If several read or write operations must be performed in succession, the master can send a repeat start condition instead of a stop condition to begin a new operation ...

  • Page 14

    ... 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. For the ADT7476A, the send byte protocol is used to write a register address to RAM for a subsequent single-byte read from the same address. This operation is illustrated in Figure 21 ...

  • Page 15

    ... TODIS = 1, SMBus timeout disabled. VIRUS PROTECTION To prevent rogue programs or viruses from accessing critical ADT7476A register settings, the lock bit can be set. Setting Bit 1 of Configuration Register 1 (0x40) sets the lock bit and locks critical registers. In this mode, certain registers can no longer be written to until the ADT7476A is powered down and powered up again ...

  • Page 16

    ... ADDITIONAL ADC FUNCTIONS FOR VOLTAGE MEASUREMENTS A number of other functions are available on the ADT7476A to offer the system designer increased flexibility. Turn-Off Averaging For each voltage/temperature measurement read from a value register, 16 readings have been made internally and the results averaged before being placed into the value register ...

  • Page 17

    ... Setting Bit 6 of Configuration Register 2 (0x73) places the ADT7476A into single-channel ADC conversion mode. In this mode, the ADT7476A can only read a single voltage channel. The selected voltage input is read every 0.7 ms. The appropriate ADC channel is selected by writing to Bits [7:5] of the TACH1 minimum high byte register (0x55) ...

  • Page 18

    ... The ADT7476A has a VID code change detect function. When Pin 21 is configured as the VID5 input, VID code changes are detected and reported back by the ADT7476A. Bit 0 of Interrupt Status Register 2 (0x42) is the 12 V/VC bit and denotes a VID change when set. The VID code change bit is set when the logic states on the VID inputs are different than they were 11 μ ...

  • Page 19

    ... V varies from device to device, and individual BE calibration is required to null this out result, this technique is unsuitable for mass production. The technique used in the ADT7476A is to measure the change in V the device is operated at two different currents. This is given by 1 ΔV = KT/q × ...

  • Page 20

    ... Some CPU manufacturers specify the high and low current levels of the substrate transistors. The high current level of the ADT7476A μA. If the ADT7476A current levels do not match LOW the current levels specified by the CPU manufacturer, it could be necessary to remove an offset. The CPU’s data sheet advises whether this offset needs to be removed and how to calculate it ...

  • Page 21

    ... Reading Temperature from the ADT7476A It is important to note that temperature can be read from the ADT7476A as an 8-bit value (with 1°C resolution 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 and in no particular order ...

  • Page 22

    ... ADT7476A Configuration Register 2 (0x73) [ averaging off. [ single-channel convert mode. TACH1 Minimum High Byte (0x55) [7:5] selects ADC channel for single-channel convert mode. Overtemperature Events Overtemperature events on any of the temperature channels can be detected and dealt with automatically in automatic fan speed control mode. Register 0x6A to Register 0x6C are the THERM temperature limits ...

  • Page 23

    ... Alternatively, SMBALERT interrupts can be generated to flag out-of-limit conditions to a processor or microcontroller. 8-Bit Limits The following is a list of 8-bit limits on the ADT7476A. Voltage Limit Registers Register 0x44, 2.5 V Low Limit = 0x00 default Register 0x45, 2.5 V High Limit = 0xFF default ...

  • Page 24

    ... If the VID code change function is used, this bit indicates a change in VID code on the VID0 to VID4 inputs. SMBALERT Interrupt Behavior The ADT7476A can be polled for status SMBALERT interrupt can be generated for out-of-limit conditions important to note how the SMBALERT output and status bits behave when writing interrupt handler software ...

  • Page 25

    ... If the TACH4 pin is being used as the THERM input, this bit masks SMBALERT for a THERM event. If the TACH4 pin is being used as GPIO6, setting this bit masks interrupts related to GPIO6. Rev Page ADT7476A CLEARED ON READ (TEMP BELOW LIMIT) TEMP BACK IN LIMIT (STATUS BIT STAYS SET) ...

  • Page 26

    ... PROCHOT output of a CPU to gauge system performance. When the THERM pin is driven low externally, the user can also set up the ADT7476A to run the fans at 100%. The fans run at 100% for the duration of time that the THERM pin is pulled low. This is done by setting the BOOST bit (Bit 2) in Configuration Register 3 (0x78 ...

  • Page 27

    ... If the THERM timer limit register (0x7A) = 0x00, the F4P bit is set. Generating SMBALERT Interrupts from THERM Timer Events The ADT7476A can generate SMBALERT s when a programmable THERM timer limit has been exceeded. This allows the system ≥ 45.52ms designer to ignore brief, infrequent THERM assertions, while capturing longer THERM timer events ...

  • Page 28

    ... Configuring the THERM Pin as an Output In addition to monitoring THERM as an input, the ADT7476A can optionally drive THERM low as an output. When PROCHOT is bidirectional, THERM can be used to throttle the processor by asserting PROCHOT ...

  • Page 29

    ... In many cases, the 4-wire fan PWM input has a built-in, pull-up resistor. The ADT7476A PWM frequency can be set to a selection of low frequencies or a single high PWM frequency. The low frequency options are used for 3-wire fans, while the high frequency option is usually used with 4-wire fans ...

  • Page 30

    ... PWM Figure 37. Driving a 4-Wire Fan Driving Two Fans from PWM3 The ADT7476A has four TACH inputs available for fan speed measurement, but only three PWM drive outputs fourth fan is being used in the system, it should be driven from the PWM3 output in parallel with the third fan. ...

  • Page 31

    ... Pin 9, Pin 11, Pin 12, and Pin 14 (when configured as TACH inputs) are high impedance inputs intended for fan speed measurement. Signal conditioning in the ADT7476A accommodates the slow rise and fall times typical of fan tachometer outputs. The maxi- mum input signal range 5.5 V, even though V 3 ...

  • Page 32

    ... SMBALERT . Measuring fan TACH has the following caveat: When the ADT7476A starts up, TACH measurements are locked. In effect, an internal read of the low byte has been made for each TACH input. The net result of this is that all TACH readings are locked until the high byte is read from the corresponding TACH registers ...

  • Page 33

    ... PWM duty cycle goes to the expected running value, for example, 33%. Fans have different spin-up characteristics and take different times to overcome inertia. The advantage of the ADT7476A is that it runs the fans just fast enough to overcome inertia and is quieter on spin-up than fans that are programmed to spin up for a given time. ...

  • Page 34

    ... In manual fan speed control mode, the ADT7476A allows the duty cycle of any PWM output to be adjusted manually. This can be useful if the user wants to change fan speed in software or adjust PWM duty cycle output for test purposes ...

  • Page 35

    ... MANUAL FAN CONTROL OVERVIEW In unusual circumstances, it can be necessary to manually control the speed of the fans. Because the ADT7476A has an SMBus interface, a system can read back all necessary voltage, fan speed, and temperature information, and use this information ...

  • Page 36

    ... ADT7476A THERMAL CALIBRATION T REMOTE 1 MIN TEMP THERMAL CALIBRATION T LOCAL MIN TEMP THERMAL CALIBRATION T REMOTE 2 MIN TEMP 100% PWM MIN PWM CONFIG PWM GENERATOR 0% T TACHOMETER 1 RANGE MEASUREMENT PWM MIN 100% PWM CONFIG PWM MUX GENERATOR TACHOMETER 2 0% MEASUREMENT T RANGE PWM MIN ...

  • Page 37

    ... This influences the choice of whether to use the TACH4 pin or to reconfigure it for the THERM function the CPU fan to be controlled using the ADT7476A, or will the CPU fan run at full speed 100% of the time? If run at 100%, this frees up a PWM output, but the system is louder ...

  • Page 38

    ... ADT7476A Recommended Implementation 1 Configuring the ADT7476A as shown in Figure 49 provides the system designer with the following features: • Six VID inputs (VID0, VID1, VID2, VID3, VID4, and VID6) for VRM10 support. • Two PWM outputs for fan control three fans. The front and rear chassis fans are connected in parallel. ...

  • Page 39

    ... Recommended Implementation 2 Configuring the ADT7476A as shown in Figure 50 provides the system designer with the following features: • Six VID inputs (VID0, VID1, VID2, VID3, VID4, and VID6) for VRM10 support. • Three PWM outputs for fan control three fans. All three fans can be individually controlled. ...

  • Page 40

    ... ADT7476A STEP 2—CONFIGURING THE MUX After the system hardware configuration is determined, the fans can be assigned to particular temperature channels. Not only can fans be assigned to individual channels, but the behavior of the fans is also configurable. For example, fans can be run under automatic fan control, manually (under software control the fastest speed calculated by multiple temperature channels ...

  • Page 41

    ... Mux Configuration Example This is an example of how to configure the mux in a system using the ADT7476A to control three fans. The CPU fan sink is controlled by PWM1, the front chassis fan is controlled by PWM2, and the rear chassis fan is controlled by PWM3. The mux is configured for the following fan control behavior: • ...

  • Page 42

    ... ADT7476A STEP 3—T SETTINGS FOR THERMAL MIN CALIBRATION CHANNELS T is the temperature at which the fans start to turn on under MIN automatic fan control. The speed at which the fan runs programmed later. The T values chosen are temperature MIN channel specific, for example, 25°C for ambient channel, 30°C for VRM temperature, and 40° ...

  • Page 43

    ... MAX should be as low as MAX limit for each fan channel. The default MAX 100% PWM MAX PWM MIN 0% T TEMPERATURE MIN Figure 56. PWM Determines Maximum PWM Duty Cycle MAX Below the THERM Temperature Limit ADT7476A register is ...

  • Page 44

    ... For example, 70°C is reached when the fans are running at 50% PWM duty cycle. Determine the slope of the required control loop to meet these requirements. Using the ADT7476A evaluation software, you can graphically program and visualize this functionality. is changed, the automatic fan control slope changes. MIN ...

  • Page 45

    ... TEMPERATURE ABOVE T MIN (B) Figure 61. T vs. Actual Fan Speed (Not PWM Drive) Profile RANGE is affected when the RANGE value is set to 20%. It can be seen that the fan actually MIN ADT7476A setting RANGE 2°C 2.5°C 3.33°C 4°C 5°C 6.67°C 8°C 10°C 13.3°C 16°C 20° ...

  • Page 46

    ... VRM temperature RANGE This example uses the mux configuration described in Step 2— Configuring the Mux with the ADT7476A connected as shown in Figure 52. Both CPU temperature and VRM temperature drive the CPU fan connected to PWM1. Ambient temperature drives the front chassis fan and rear chassis fan connected to PWM2 and PWM3 ...

  • Page 47

    ... Relates to Automatic Fan Control THERM Rev Page between normal speed and off, MIN RAMP PWM CONTROL PWM1 (ACOUSTIC ENHANCEMENT) TACH1 CPU FAN SINK RAMP CONTROL PWM PWM2 (ACOUSTIC ENHANCEMENT) TACH2 FRONT CHASSIS RAMP CONTROL PWM PWM3 (ACOUSTIC ENHANCEMENT) TACH3 AND 4 REAR CHASSIS ADT7476A ...

  • Page 48

    ... ADT7476A STEP 8—T FOR TEMPERATURE CHANNELS HYST T is the amount of extra cooling a fan provides after the HYST temperature measured has dropped back below T the fan turns off. The premise for temperature hysteresis (T is that without it, the fan would merely chatter, or cycle on ...

  • Page 49

    ... 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. As the detection time only takes 5 ms, programming the PWM outputs to 100% and then back to its normal speed is not noticeable in most cases. Rev Page ADT7476A ...

  • Page 50

    ... PWM output is not pulled to a voltage higher than the maximum allowable voltage on that pin (5.5 V). FAN SYNC When two ADT7476As are used in a system possible to synchronize them so that one PWM channel from each device can be effectively OR’ together to create a PWM output that reflects the maximum speed of the two OR’ ...

  • Page 51

    ... REGISTER TABLES Table 18. ADT7476A Registers Address R/W Description Bit 7 0x10 R/W Configuration ExtraSlow Register 6 0x11 R/W Configuration RES Register 7 0x20 R 2 Measurement 0x21 CCP Measurement 0x22 Measurement 0x23 Measurement 0x24 Measurement 0x25 R Remote 1 9 Temperature 0x26 R Local ...

  • Page 52

    ... ADT7476A Address R/W Description Bit 7 0x49 R/W V High Limit 7 CC 0x4A R Low Limit 7 0x4B R High Limit 7 0x4C R Low Limit 7 0x4D R High Limit 7 0x4E R/W Remote 1 Temp 7 Low Limit 0x4F R/W Remote 1 Temp 7 High Limit 0x50 R/W Local Temp 7 Low Limit 0x51 R/W Local Temp ...

  • Page 53

    ... FAN2 Local R1 VID/ GPIO GPIO6P THERM THERM (O/P (O/P Only) Only) BpAtt BpAtt BpAtt 2.5 V MaxSpeed THERM CCP Do not write to these registers Do not write to these registers Rev Page ADT7476A Bit 2 Bit 1 Bit 0 Default 0X5A 0X5A 0X64 0X64 2 ...

  • Page 54

    ... THERM in Read/Write When this bit is set, THERM is enabled in manual mode Manual [4] SlaveEn Read/Write Setting this bit configures the ADT7476A as a slave for use in fan sync mode. [5] MasterEn Read/Write Setting this bit configures the ADT7476A as a master for use in fan sync mode. [6] V ...

  • Page 55

    ... A count of 0xFFFF indicates that a fan is one of the following: stalled or blocked (object jamming the fan), failed (internal circuitry destroyed), or not populated. (The ADT7476A expects to see a fan connected to each TACH 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 ...

  • Page 56

    ... ADT7476A is powered down and powered up again. This prevents rogue programs such as viruses from modifying critical system limit settings. (Lockable.) [2] RDY Read-only This bit is set the ADT7476A to indicate that the device is fully powered-up and ready to begin system monitoring. [3] FSPD Read/Write When set to 1, this bit runs all fans at max speed as programmed in the max PWM current duty cycle registers (0x30 to 0x32) ...

  • Page 57

    ... CCP V high limit. CCP V low limit high limit low limit high limit low limit high limit. Rev Page ADT7476A . HYST > 1.7 V). IH < 0 > 0.8 V Power-On Default 0x00 0xFF 0x00 0xFF 0x00 0xFF ...

  • Page 58

    ... ADT7476A Table 31. Temperature Limit Registers Register Address R/W 0x4E Read/Write 0x4F Read/Write 0x50 Read/Write 0x51 Read/Write 0x52 Read/Write 0x53 Read/Write 1 Exceeding any of these temperature limits by 1°C 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 ...

  • Page 59

    ... Fastest speed calculated by local and Remote 2 temperature controls PWMx. 110 = Fastest speed calculated by all three temperature channel controls PWMx. 111 = Manual mode. PWM current duty cycle registers (0x30 to 0x32) become writable. Rev Page ADT7476A Power-On Default 0x62 0x62 0x62 ...

  • Page 60

    ... ADT7476A Table 35. T /PWM Frequency Registers RANGE 1 Register Address R/W 0x5F Read/Write 0x60 Read/Write 0x61 Read/Write Bit Name R/W [2:0] FREQ Read/Write [3] HF/LF Read/Write [7:4] RANGE Read/Write 1 These registers become read-only when the Configuration Register 1 lock bit is set. Any further attempts to write to these registers have no effect. ...

  • Page 61

    ... PWM 2 minimum duty cycle below T [7] MIN3 Read/Write When the ADT7476A is in automatic fan speed control mode, this bit defines whether PWM3 is off (0% duty cycle PWM3 minimum duty cycle when the controlling temperature is below its duty cycle below PWM3 minimum duty cycle below T 1 This register becomes read-only when the Configuration Register 1 lock bit is set to 1 ...

  • Page 62

    ... ADT7476A Table 37. Register 0x63—Enhance Acoustics Register 2 (Power-On Default = 0x00) 1 Bit Name R/W Description [2:0] ACOU3 Read/Write Assuming that PWMx is associated with the local temperature channel, these bits define the maximum rate of change of the PWMx output for local temperature-related changes. Instead of the fan speed jumping instantaneously to its newly determined speed, it ramps gracefully at the rate determined by these bits ...

  • Page 63

    ... Register Address R/W 0x64 Read/Write 0x65 Read/Write 0x66 Read/Write 1 Bit Name R/W [7:0] PWM duty cycle Read/Write 1 These registers become read-only when the ADT7476A is in automatic fan control mode. 1 Table 39. T Registers MIN 2 Register Address R/W 0x67 Read/Write 0x68 Read/Write 0x69 Read/Write 1 These are the T registers for each temperature channel ...

  • Page 64

    ... ADT7476A Table 42. XNOR Tree Test Enable 1 Register Address R/W Description 0x6F Read/Write XNOR tree test enable register. [0] XEN 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. ...

  • Page 65

    ... Bits [7:4] of Configuration Register 4 (0x7D). CONV = 1 indicates that the ADT7476A is put into a single-channel ADC conversion mode. In this mode, the ADT7476A can be made to read continuously from one input only, for example, Remote 1 temperature. The appropriate ADC channel is selected by writing to Bits [7:5] of TACH1 minimum high byte register (0x55). ...

  • Page 66

    ... ADT7476A Table 48. Register 0x75—Interrupt Mask Register 2 (Power-On Default [7:0] = 0x00) Bit Name R V/VC Read/Write 1 OVT Read Only 2 FAN1 Read/Write 3 FAN2 Read/Write 4 FAN3 Read/Write 5 F4P Read/Write 6 D1 Read/Write 7 D2 Read/Write Table 49. Register 0x76—Extended Resolution Register 1 Bit Name R/W [1:0] 2.5 V Read-only [3:2] V Read-only CCP [5:4] V Read-only ...

  • Page 67

    ... 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. 5.82 sec to be reported back with a resolution of 22.76 ms. Rev Page ADT7476A Pin 22 Pin 14 +2.5V TACH4 IN +2 ...

  • Page 68

    ... ADT7476A Table 54. Register 0x7B—TACH Pulses per Revolution Register (Power-On Default = 0x55) Bit Name R/W Description [1:0] FAN1 Read/Write 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 (default) ...

  • Page 69

    ... Read/Write 2sC = 1 sets the temperature range to the twos complement temperature range. 2sC = 0 changes the temperature range to the Offset 64 temperature range. When this bit is changed, the ADT7476A interprets all relevant temperature register values as defined by this bit. [1] TempOffset Read/Write TempOffset = 0 sets offset range to −63°C to +64°C with 0.5°C resolution. ...

  • Page 70

    ... ADT7476A Table 56. Register 0x7D—Configuration Register 4 (Power-On Default = 0x00) 1 Bit Name R/W Description [1:0] PIN14FUNC Read/Write These bits set the functionality of Pin 14: [2] THERM Read/Write THERM Disable = 0 enables THERM overtemperature output assuming THERM is correctly configured Disable (Register 0x78, Register 0x7C, and Register 0x7D). ...

  • Page 71

    ... COMPLIANT TO JEDEC STANDARDS MO-137AE Figure 67. 24-Lead Shrink Small Outline Package [QSOP] (RQ-24) Dimensions shown in inches Package Description 24-Lead Shrink Small Outline Package [QSOP] 24-Lead Shrink Small Outline Package [QSOP] 24-Lead Shrink Small Outline Package [QSOP] Rev Page ADT7476A 8° 0° 0.050 0.016 Package Option RQ-24 RQ-24 RQ-24 ...

  • Page 72

    ... ADT7476A NOTES ©2006 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D05742-0-1/06(0) Rev Page ...