Datasheet

6-Channel Intelligent Fan Controller

MAX31785

FAN_COMMAND_1 (3Bh)

The FAN_COMMAND_1 command is used to override the device’s automatic fan-control function and force the fan to

either a fixed PWM duty-cycle value or a target fan speed (in RPM). The units of FAN_COMMAND_1 are either percent

duty cycle (if bit 6 of FAN_CONFIG_1_2 is zero) or RPM (if bit 6 of FAN_CONFIG_1_2 is one). Any value less than 0%

duty cycle or 0 RPM causes the device to ignore this command and use the automatic fan-control function. Any value

greater than or equal to 0% duty cycle or 0 RPM causes the device to ignore the automatic fan-control function and

force the fan to the PWM value or RPM value provided by the FAN_COMMAND_1 command. The 2 data bytes are in

DIRECT format.

Table 14. PWM Fan Mode (FAN_CONFIG_1_2 Bit 6 = 0)

Table 15. RPM Fan Mode (FAN_CONFIG_1_2 Bit 6 = 1)

VOUT_OV_FAULT_LIMIT (40h)

The VOUT_OV_FAULT_LIMIT command sets the value of the output voltage that causes an output overvoltage fault.

The monitored voltage must drop by at least 2% below the limit before the fault is allowed to clear. The 2 data bytes

are in DIRECT format. In response to the VOUT_OV_FAULT_LIMIT being exceeded, the device does the following:

1) Sets the VOUT_OV bit in STATUS_BYTE.

2) Sets the VOUT_OV and VOUT bits in STATUS_WORD.

3) Sets the VOUT_OV_FAULT bit in STATUS_VOUT.

4) Responds as specified in the MFR_FAULT_RESPONSE.

5) Notifies the host through ALERT assertion (if enabled in MFR_MODE).

VOUT_OV_WARN_LIMIT (42h)

The VOUT_OV_WARN_LIMIT command sets the value of the output voltage that causes an output-voltage high warn-

ing. This value is typically less than the output overvoltage threshold in VOUT_OV_FAULT_LIMIT. The monitored volt-

age must drop by at least 2% below the limit before the warning is allowed to clear. The 2 data bytes are in DIRECT

format. In response to the VOUT_OV_WARN_LIMIT being exceeded, the device does the following:

1) Sets the NONE OF THE ABOVE bit in STATUS_BYTE.

2) Sets the NONE OF THE ABOVE and VOUT bits in STATUS_WORD.

3) Sets the VOUT_OV_WARN bit in STATUS_VOUT.

4) Notifies the host using ALERT assertion (if enabled in MFR_MODE).

FAN_COMMAND_1 VALUE DEVICE RESPONSE

8000h to FFFFh Ignore FAN_COMMAND_1 and use automatic fan-control function

0000h to 2710h 0 to 100% fan PWM duty cycle

2711h to 7FFFh 100% fan PWM duty cycle

FAN_COMMAND_1 VALUE DEVICE RESPONSE

8000h to FFFFh Ignore FAN_COMMAND_1 and use automatic fan-control function

0000h to 7FFFh 0 to 32,767 RPM