ADT7476 Analog Devices, Inc., ADT7476 Datasheet
ADT7476
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ADT7476 Summary of contents
Page 1
... 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 two remote sensor diodes plus its own internal temperature, and measure and control the speed four fans so they operate at the lowest possible speed for minimum acoustic noise ...
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... Timing Diagram ........................................................................... 5 Absolute Maximum Ratings............................................................ 6 Thermal Resistance ...................................................................... 6 ESD Caution.................................................................................. 6 Pin Configuration and Function Descriptions............................. 7 Typical Performance Characteristics ............................................. 9 Product Description....................................................................... 11 Feature Comparisons Between ADT7476 and ADT7468..... 11 Recommended Implementation............................................... 12 Serial Bus Interface..................................................................... 13 Write Operations ........................................................................ 15 Read Operations ......................................................................... 16 SMBus Timeout .......................................................................... 16 Virus Protection.......................................................................... 16 Voltage Measurement Input...................................................... 17 Analog-to-Digital Converter ...
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... Changes to Bit 1 in Table 51...........................................................68 3/06—Rev Rev. A Changes to Features Section ............................................................1 Changes to Table 1 ............................................................................4 Inserted Table 3..................................................................................6 Changes to Feature Comparisons Between ADT7476 and ADT7468 Section ............................................................................11 Changes to Figure 23 ......................................................................16 Changes to Fan Speed Measurement Registers Section.............34 Changes to Register Tables Section...............................................53 Changes to Ordering Guide...........................................................72 4/05— ...
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... ADT7476 SPECIFICATIONS unless otherwise noted. A MIN MAX CC MIN MAX Table 1. Parameter POWER SUPPLY Supply Voltage Supply Current TEMPERATURE-TO-DIGITAL CONVERTER Local Sensor Accuracy Resolution Remote Diode Sensor Accuracy Resolution Remote Sensor Source Current ANALOG-TO-DIGITAL CONVERTER ...
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... 0.4 V μ μ See Figure 2 400 kHz 50 ns μs μs 50 μs 1000 ns 300 μ Can be disabled = 25°C and represent a most likely parametric norm. Logic inputs A = 0.8 V for a falling edge HD; STA t t SU; STA SU; STO S ADT7476 P ...
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... ADT7476 ABSOLUTE MAXIMUM RATINGS Table 2. Parameter Positive Supply Voltage ( Maximum Voltage on +12V Pin IN Maximum Voltage on +5V Pin IN Maximum Voltage on All Open-Drain Outputs Voltage on Any Input or Output Pin Input Current at Any Pin Package Input Current Maximum Junction Temperature ( MAX Storage Temperature Range ...
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... Digital I/O (Open Drain). Pulse-width modulated output to control Fan 3 and Fan 4 speed. Requires 10 kΩ typical pull-up. Can be configured as a high or low frequency drive. ADDREN If pulled low on power-up, the ADT7476 enters address select mode, and the state of Pin 14 (ADDR SELECT) determines the ADT7476 slave address. 14 TACH4 Digital Input (Open Drain) ...
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... ADT7476 Pin No. Mnemonic Description 17 D1– Cathode Connection to First Thermal Diode. 18 D1+ Anode Connection to First Thermal Diode. 19 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. 20 +5V Analog Input. Monitors +5 V power supply. ...
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... NOISE FREQUENCY (Hz) 1.20 1.18 1.16 1.14 1.12 1.10 1.08 1.06 1.04 1.02 1.00 0.98 3.0 3.1 3.2 3.3 3.4 V (V) DD Figure 8. Normal I vs. Power Supply 100mV 0 250mV –5 –10 –15 0 100M 200M 300M 400M FREQUENCY (Hz) Figure 9. Internal Temperature Error vs. Power Supply ADT7476 500M 600M 3.5 3.6 500M 600M ...
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... ADT7476 6 4 250mV 2 0 –2 100mV –4 –6 –8 –10 –12 0 100M 200M 300M FREQUENCY (Hz) 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. Temperature 400M 500M ...
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... PRODUCT DESCRIPTION The ADT7476 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) ...
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... ADT7476 RECOMMENDED IMPLEMENTATION Configuring the ADT7476, as shown in Figure 13, allows the system designer to use the following features: • Two PWM outputs for fan control three fans. (The front and rear chassis fans are connected in parallel.) • Three TACH fan speed measurement inputs. ...
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... The ADT7476 is connected to this bus as a slave device, under the control of a master controller. The ADT7476 has a 7-bit serial bus address. When the device is powered up with Pin 13 (PWM3/ ADDREN ) high, the ADT7476 has a default SMBus address of 0101110 or 0x2E. The read/write bit must be added to get the 8-bit address ...
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... Figure 18. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register On PCs and servers, control of the ADT7476 is carried out using the SMBus. The ADT7476 is connected to this bus as a slave device, under the control of a master controller, which is usually (but not necessarily) the ICH. ...
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... The master asserts a stop condition on SDA, and the transaction ends. For the ADT7476, 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. If the master is required to read data from the register immedi- ...
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... Bit 6 TODIS = 1, SMBus timeout enabled VIRUS PROTECTION To prevent rogue programs or viruses from accessing critical ADT7476 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 ...
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... MUX register. ADDITIONAL ADC FUNCTIONS FOR VOLTAGE MEASUREMENTS Several other functions are available on the ADT7476 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 ...
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... Setting Bit 6 of Configuration Register 2 (0x73) places the ADT7476 into single-channel ADC conversion mode. In this mode, the ADT7476 can read a single voltage channel only. 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) ...
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... ADT7476 ...
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... The ADT7476 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 ADT7476. 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 ...
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... D– input and the emitter to the D+ input NPN transistor is used, the emitter is connected to the D– input and the base to the D+ input. Figure 25 and Figure 26 show how to connect the ADT7476 to an NPN or PNP transistor for temperature measurement. To prevent ground noise from interfering with the measurement, the more negative terminal of the sensor is not referenced to ground but is biased above ground by an internal diode at the D– ...
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... ADT7476 180 μA and the low level current, HIGH μA. If the ADT7476 current levels do not match LOW the current levels specified by the CPU manufacturer, it might be necessary to remove an offset. The data sheet for the CPU advises whether this offset needs to be removed and how to calculate it ...
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... Reading Temperature from the ADT7476 It is important to note that temperature can be read from the ADT7476 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 ...
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... Single-Channel ADC Conversions Setting Bit 6 of Configuration Register 2 (0x73) places the ADT7476 into single-channel ADC conversion mode. In this mode, the ADT7476 can be made to read a single temperature channel only. The appropriate ADC channel is selected by writing to Bits [7:5] of the TACH1 minimum high byte register (0x55). ...
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... 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 ADT7476. Voltage Limit Registers Register 0x44, 2.5 V Low Limit = 0x00 default Register 0x45, 2.5 V High Limit = 0xFF default ...
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... If the VID code change function is used, this bit indicates a change in VID code on the VID0 to VID5 inputs. SMBALERT Interrupt Behavior The ADT7476 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 ...
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... VID code change, depending on the function used. Rev Page CLEARED ON READ (TEMP BELOW LIMIT) TEMP BACK IN LIMIT (STATUS BIT STAYS SET) INTERRUPT MASK BIT SET INTERRUPT MASK BIT CLEARED (SMBALERT REARMED masks SMBALERT for V channel masks SMBALERT for V channel. CCP ADT7476 ...
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... THERM pin. This can be useful for connect- ing to the PROCHOT output of a CPU to gauge system performance. The user can also set up the ADT7476 so that, when the THERM pin is driven low externally, the fans run at 100%. The fans run at 100% for the duration of the time that the THERM pin is pulled low ...
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... Generating SMBALERT Interrupts from THERM Timer Events The ADT7476 can generate an SMBALERT when a programmable THERM timer limit is exceeded. This allows the system designer to ignore brief, infrequent THERM assertions while capturing longer THERM timer events. Register 0x7A is ≥ 45.52ms the THERM timer limit register ...
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... Configuring the THERM Pin as an Output In addition to monitoring THERM as an input, the ADT7476 can optionally drive THERM low as an output. When PROCHOT is bidirectional, THERM can be used to throttle the processor by asserting PROCHOT . The user can preprogram system-critical thermal limits. If the temperature exceeds a thermal limit by 0.25° ...
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... In many cases, the 4-wire fan PWM input has a built-in pull-up resistor. The ADT7476 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 ...
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... Figure 37. Driving a 4-Wire Fan Driving Two Fans from PWM3 The ADT7476 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. ...
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... 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 ADT7476 accommodates the slow rise and fall times typical of fan tachometer outputs. The maxi- mum input signal range 3.6 V, even though V 3 ...
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... SMBALERT . Measuring fan TACH has the following caveat: when the ADT7476 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 ...
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... Fan Spin-Up The ADT7476 has a unique fan spin-up function. It spins the fan at 100% PWM duty cycle until two TACH pulses are de- tected on the TACH input. Once two TACH pulses are detected, the PWM duty cycle goes to the expected running value, for example, 33% ...
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... The advantage is that, if the system hangs, the user is guaranteed that the system is protected from overheating. In manual fan speed control mode, the ADT7476 allows the duty cycle of any PWM output to be manually adjusted. This can be useful if the user wants to change fan speed in software or adjust PWM duty cycle output for test purposes ...
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... PWM outputs. The three PWM outputs can be used to control up to four fans. The ADT7476 allows the speed of four fans to be monitored. Each temperature channel has a thermal calibration block, allowing the designer to individually configure the thermal characteristics of each temperature channel ...
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... This influences the choice of whether to use the TACH4 pin or to reconfigure it for the THERM function. • Is the CPU fan to be controlled using the ADT7476, or will the CPU fan run at full speed 100% of the time? Running at 100% frees up a PWM output, but the system is louder. ...
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... VRM TEMP T MIN REMOTE 2 = CPU TEMP Recommended Implementation 1 Configuring the ADT7476 as shown in Figure 49 provides the system designer with the following features: • Six VID inputs (VID0 to VID5) for VRM10 support. • Two PWM outputs for fan control three fans. The front and rear chassis fans are connected in parallel. • ...
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... REAR CHASSIS FAN AMBIENT TEMPERATURE Recommended Implementation 2 Configuring the ADT7476 as in Figure 50 provides the system designer with the following features: • Six VID inputs (VID0 to VID5) for VRM10 support. • Three PWM outputs for fan control three fans. All three fans can be individually controlled. ...
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... PWMx runs full speed 100 = PWMx is disabled (default) 111 = manual mode. In manual mode, PWMx runs under software control. In this mode, PWM duty cycle registers (Register 0x30 to Register 0x32) are writable and control the PWM outputs. Rev Page ADT7476 CPU FAN CPU ICH ...
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... CPU TEMP Mux Configuration Example This is an example of how to configure the mux in a system using the ADT7476 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: • ...
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... ENHANCEMENT) TACH2 FRONT CHASSIS RAMP CONTROL PWM3 (ACOUSTIC ENHANCEMENT) TACH3 REAR CHASSIS = 0x5A (90°C) MIN = 0x5A (90°C) MIN = 0x5A (90°C) MIN − MIN HYST − MIN HYST − MIN HYST − MIN HYST − MIN HYST − MIN HYST ADT7476 ...
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... ADT7476 100 MIN THERMAL CALIBRATION T MIN THERMAL CALIBRATION REMOTE 2 = CPU TEMP T MIN LOCAL = THERMAL CALIBRATION VRM TEMP T MIN REMOTE 1 = AMBIENT TEMP STEP 4: PWM FOR EACH PWM (FAN) OUTPUT MIN PWM is the minimum PWM duty cycle at which each fan in MIN the system runs also the start speed for each fan under ...
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... Below the THERM Temperature Limit Registers MAX registers are 8-bit registers that allow the MAX Value (decimal) = PWM /0.39 MAX Value (decimal) − 50/0.39 = 128 (decimal) Value = 128 (decimal (hex) Value (decimal) = 75/0. (decimal) Value = 192 (decimal (hex) Registers MAX ADT7476 register is MAX ...
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... PWM duty cycle. 3. Determine the slope of the required control loop to meet these requirements. 4. Using the ADT7476 evaluation software, graphically program and visualize this functionality. Ask your local Analog Devices, Inc. representative for details. As PWM is changed, the automatic fan control slope changes. ...
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... MIN (B) Figure 61. T vs. Actual Fan Speed (Not PWM Drive) Profile RANGE , needs to be factored in to see how the loop actually MIN value is set to 20%. It can be seen that the MIN . MIN ADT7476 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° ...
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... VRM temperature RANGE This example uses the MUX configuration described in Step 2: Configuring the Mux, with the ADT7476 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 ...
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... Rev Page between normal speed and off, creating unsettling MIN RAMP PWM CONTROL PWM1 (ACOUSTIC ENHANCEMENT) TACH1 CPU FAN SINK RAMP PWM CONTROL PWM2 (ACOUSTIC ENHANCEMENT) TACH2 FRONT CHASSIS RAMP PWM CONTROL PWM3 (ACOUSTIC ENHANCEMENT) TACH3 AND 4 REAR CHASSIS ADT7476 ...
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... ADT7476 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 fan turns off. The premise for temperature hysteresis (T that, without it, the fan would merely chatter, or cycle on and off regularly, whenever the temperature is hovering at about the T setting ...
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... Read the state of Bits [3:1] of Configuration Register 2 (0x73). The state of these bits reflects whether a 4-wire fan is connected directly to the PWM output. Because 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 ADT7476 ...
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... This ensures that the PWM output is not pulled to a voltage higher than the maximum allowable voltage on that pin (3.6 V). FAN SYNC When two ADT7476s 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’ ...
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... REGISTER TABLES Table 18. ADT7476 Registers Address R/W Description Bit 7 0x10 R/W Configuration Extra Register 6 Slow 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 ...
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... ADT7476 Address R/W Description Bit 7 0x42 R/W Interrupt Status D2 Register 2 FAULT 0x43 R/W VID Code VIDSEL 0x44 R/W 2.5 V Low Limit 7 0x45 R/W 2.5 V High Limit 7 0x46 R/W V Low Limit 7 CCP 0x47 R/W V High Limit 7 CCP 0x48 R/W V Low Limit 7 CC 0x49 R/W V High Limit 7 CC 0x4A R Low Limit 7 0x4B R High Limit ...
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... BOOST THERM / ALERT Enable 2.5V TMR TMR ASRT/TMRO LIMT LIMT LIMT FAN2 FAN1 FAN1 GPIO6D Temp TWOS COMPL Offset ADT7476 Default Lockable 0x00 Yes 0x80 Yes 0x80 Yes 0x80 Yes 0x5A Yes 0x5A Yes 0X5A Yes 0x64 Yes 0x64 Yes ...
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... Register 0x63). [3] THERM in R/W When this bit is set, THERM is enabled in manual mode. Manual [4] SlaveEn R/W Setting this bit configures the ADT7476 as a slave for use in fan sync mode. [5] MasterEn R/W Setting this bit configures the ADT7476 as a master for use in fan sync mode. [6] V Low R/W V Low = 1 ...
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... Failed (internal circuitry destroyed). • Not populated. (The ADT7476 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. ...
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... RDY Read-only This bit is set the ADT7476 to indicate only that the device is fully powered up and ready to begin system monitoring. [3] FSPD R/W When set to 1, this bit runs all fans at maximum speed as programmed in the PWM maximum duty cycle registers (0x38 to 0x3A) ...
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... Selects the input switching threshold for the VID inputs. THLD = 0 selects a threshold THLD = 1 lowers the switching threshold to 0 [7] VIDSEL R/W VIDSEL = 0 configures Pin 21 as the 12 V measurement input (default). < 0 > 1.7 V < 0 > 0.8 V Rev Page ADT7476 . HYST ...
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... ADT7476 1 Table 30. Voltage Limit Registers Register Address R/W 0x44 R/W 0x45 R/W 0x46 R/W 0x47 R/W 0x48 R/W 0x49 R/W 0x4A R/W 0x4B R/W 0x4C R/W 0x4D R/W 1 Setting the Configuration Register 1 LOCK bit has no effect on these registers. 2 High limits: An interrupt is generated when a value exceeds its high limit (>comparison). Low limits: An interrupt is generated when a value is equal to or below its low limit (≤ ...
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... Fastest speed calculated by local and Remote 2 temperature controls PWMx. 110 = Fastest speed calculated by all three temperature channel controls PWMx. 111 = Manual mode. PWM duty cycle registers (Register 0x30 to Register 0x32) become writable. Description PWM1 configuration PWM2 configuration PWM3 configuration Rev Page ADT7476 Power-On Default 0x62 0x62 0x62 ...
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... ADT7476 Table 36. TEMP T /PWM Frequency Registers RANGE 1 Register Address R/W 0x5F R/W 0x60 R/W 0x61 R/W 1 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. Register 0x5F, Register 0x60, and Register 0x61—TEMP T Bit Name ...
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... PWM2 minimum duty cycle below T [7] MIN3 R/W When the ADT7476 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 T value 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 ...
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... ADT7476 Table 39. Register 0x63—Enhanced Acoustics Register 2 (Power-On Default = 0x00) Bit Name R/W 1 Description [2:0] ACOU3 R/W 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 ...
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... Table 40. PWMx Minimum Duty Cycle Registers Register Address R/W 1 0x64 R/W 0x65 R/W 0x66 R/W 1 These registers become read-only when the ADT7476 is in automatic fan control mode. Table 41. Register 0x64, Register 0x65, Register 0x66—PWMx Minimum Duty Cycle Registers (Power-On Default = 0x80; 50% duty cycle) 1 Bit Name R/W [7:0] PWM duty cycle R/W 1 These registers become read-only when the ADT7476 is in automatic fan control mode ...
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... ADT7476 1 Table 43. THERM Limit Registers 2 Register Address R/W 0x6A R/W 0x6B R/W 0x6C R 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. The PWM output remains at 100% until the temperature drops below THERM limit – ...
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... CONV R/W CONV = 1, the ADT7476 is put into a single-channel ADC conversion mode. In this mode, the ADT7476 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 TACH 1 minimum high byte register (0x55). Register 0x55, Bits [7:5] ...
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... ADT7476 Table 50. Register 0x74—Interrupt Mask Register 1 (Power-On Default = 0x00) Bit Name R/W Description [0] 2.5 V/ THERM R/W 2.5 V/ THERM = 1, masks SMBALERT for out-of-limit conditions on the 2.5 V/ THERM [1] V R/W V CCP CCP [ [ masks SMBALERT for out-of-limit conditions on the 5 V channel. ...
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... 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. Times how long THERM input is asserted. These seven bits read zero until the THERM assertion time exceeds 45.52 ms. Rev Page ADT7476 Pin 22 Pin 14 +2.5 V TACH4 +2.5 V THERM +2 ...
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... R/W TWOS COMPL = 1, sets the temperature range to the twos complement temperature range. COMPL TWOS COMPL = 0, changes the temperature range to the Offset 64 temperature range. When this bit is changed, the ADT7476 interprets all relevant temperature register values as defined by this bit. [1] Temp Offset R/W TempOffset = 0, sets offset range to −63°C to +64°C with 0.5°C resolution. ...
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... SMBALERT 11 = GPIO6 In Offset 64 mode, writing −64°C to the appropriate THERM temperature limit. In twos complement mode, writing −128°C to the appropriate THERM temperature limit. attenuator. When set, the measurement scale for this channel changes from 0 V (0x00) to CCP Rev Page ADT7476 ...
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... ADT7476ARQZ-REEL –40°C to +125°C ADT7476ARQZ-REEL7 1 –40°C to +125°C 1 EVAL-ADT7476EBZ 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) 0.345 0.341 0.337 ...