ADT7470 Analog Devices, Inc., ADT7470 Datasheet - Page 27

• Manufacturer Part Number: ADT7470
• Description: Temperature Sensor Hub And Fan Controller
• Manufacturer: Analog Devices, Inc.

Readings from daisy-chained TMP05 are processed and loaded into the temperature reading registers.
Table 22. Register 0x20 to Register 0x29. Temperature Reading Registers (Power-On Default = 0x00)
Register Address
0x20
0x21
0x22
0x23
0x24
0x25
0x26
0x27
0x28
0x29
The fan tach reading registers shown in Table 23 count the number of 11.11 µs periods (based on an internal 90 kHz clock) that occur
between a number of consecutive fan tach pulses (default = 2). The number of tach pulses used to count can be changed using the fan
pulses per revolution register (Register 0x43). This allows the fan speed to be accurately measured. Because a valid fan tachometer
reading requires that two bytes are read, the low byte MUST be read first. Both the low and high bytes are then frozen until read. At
power-on, these registers contain 0x0000 until such time as the first valid fan tach measurement is read in to these registers. This prevents
false interrupts from occurring while the fans are spinning up.
A count of 0xFFFF indicates that a fan is
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Table 23. Register 0x2A to Register 0x31. Fan Tach Reading Registers (Power-On Default = 0x00)
Register Address
0x2A
0x2B
0x2C
0x2D
0x2E
0x2F
0x30
0x31
The current PWM duty cycle registers, shown in Table 24, reflect the PWM duty cycle driving each fan at any given time. When in
automatic fan speed control mode, the ADT7470 reports the PWM duty cycles back through these registers. The PWM duty cycle values
vary according to temperature in automatic fan speed control mode. During fan startup, these registers report back 0x00. In software
mode, the PWM duty cycle outputs can be set to any duty cycle value by writing to these registers.
Table 24. Register 0x32 to Register 0x35. Current PWM Duty Cycle Registers (Power-On Default = 0xFF)
Register Address
0x32
0x33
0x34
0x35
The TEST bit in the Configuration Register (Register 0x40) invokes a fan free-wheeling test to determine how many fans are connected to
the part. The results of the fan test are reflected in the fans-not-present register, shown in Table 25.
Stalled or blocked (object jamming the fan).
Failed (internal circuitry destroyed).
Not populated. The ADT7470 expects to see a fan connected to each tach. If a fan is not connected to that tach,
its tach minimum high and low byte should be set to 0xFFFF.
Read/Write
Read-only
Read-only
Read-only
Read-only
Read-only
Read-only
Read-only
Read-only
Read/Write
Read-only
Read-only
Read-only
Read-only
Read-only
Read-only
Read-only
Read-only
Read-only
Read-only
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
Description
PWM1 Current Duty Cycle (0% to PWMMAX duty cycle = 0x00 to 0xFF).
PWM2 Current Duty Cycle (0% to PWMMAX duty cycle = 0x00 to 0xFF).
PWM3 Current Duty Cycle (0% to PWMMAX duty cycle = 0x00 to 0xFF).
PWM4 Current Duty Cycle (0% to PWMMAX duty cycle = 0x00 to 0xFF).
Description
Temperature 1 Reading (from TMP05 sensor).
Temperature 2 Reading (from TMP05 sensor).
Temperature 3 Reading (from TMP05 sensor).
Temperature 4 Reading (from TMP05 sensor).
Temperature 5 Reading (from TMP05 sensor).
Temperature 6 Reading (from TMP05 sensor).
Temperature 7 Reading (from TMP05 sensor).
Temperature 8 Reading (from TMP05 sensor).
Temperature 9 Reading (from TMP05 sensor).
Temperature 10 Reading (from TMP05 sensor).
Description
Tach 1 Low Byte (8 MSBs of reading).
Tach 1 High Byte (8 LSBs of reading).
Tach 2 High Byte (8 MSBs of reading).
Tach 2 Low Byte (8 LSBs of reading).
Tach 3 High Byte (8 MSBs of reading).
Tach 3 Low Byte (8 LSBs of reading).
Tach 4 High Byte (8 MSBs of reading).
Tach 4 Low Byte (8 LSBs of reading).
Rev. B | Page 27 of 40
ADT7470