Datasheet

6-Channel Intelligent Fan Controller
MAX31785
41
MFR_FAN_CONFIG (F1h)
The MFR_FAN_CONFIG command is used with FAN_CONFIG_1_2 to configure the fan. See the FAN_CONFIG_1_2
description for more details on this command. Table 26 describes the MFR_FAN_CONFIG command.
Table 26. MFR_FAN_CONFIG
BIT BIT NAME MEANING
15:13 FREQ[2:0]
The FREQ bits set the PWM frequency. Note: The device does not support pulse stretching.
FREQ2 FREQ1 FREQ0 PWM FREQUENCY
0 0 0 30Hz
0 0 1 50Hz
0 1 0 100Hz
0 1 1 150Hz
1 0 0 Reserved
1 0 1 Reserved
1 1 0 Reserved
1 1 1 25kHz
12 DUAL_TACH
0 = Dual tach functionality is disabled.
1 = Dual tach functionality is enabled.
Note: In dual tachometer applications, it is recommended that the slower tachometer signal be
presented to the TACH pin when TACHSEL = 0.
11:10 HYS[1:0]
The HYS bits determine the amount of hysteresis the device uses to determine how far the tem-
perature must fall below the temperature level threshold programmed in the LUT before switch-
ing to the lower PWM/RPM value. The hysteresis should be set lower than the minimum differ-
ence between two adjacent temperature steps. These bits are ignored if automatic fan control is
disabled.
HSY1 HSY0
THERMAL HYSTERESIS (NC)
0 0 2
0 1 4
1 0 6
1 1 8
9 TSFO
0 = Ramp to 100% PWM duty cycle if temp sensor faults (automatic fan mode) or if no
FAN_COMMAND_1 update occurs (manual fan mode) in any 10s period.
1 = Temp sensor fault or update rate to FAN_COMMAND_1 is ignored. Operate at the last
updated PWM/RPM value.
Note 1: A temp sensor fault is a faulty temperature sensor reading, not an overtemperature fault.
Note 2: In automatic fan mode, if the TSFO bit is set to 1, the device ignores a sensor fault and
uses the remaining assigned temperature sensors (if any) to control the fan PWM duty cycle; or,
if the fan has no available temperature sensors to use, it maintains the last updated PWM/RPM
fan value before the fault occurred.
8 TACHO
0 = Ramp fan to 100% PWM duty cycle if fan fault is detected.
1 = Do not ramp fan to 100% PWM duty cycle if fan fault is detected.
Note: If the fan fault is removed after ramping the PWM to 100% duty cycle, normal fan opera-
tion is resumed.