Datasheet

6-Channel Intelligent Fan Controller

MAX31785

Table 8. Fan Health Conditions

fan’s PWM duty cycle is between 40% and 80%. The

masured fan speed is also compared to the expected

at 100% duty cycle. In the 40% to 80% range, a fan’s

expected fan-speed profile is approximately linear. At

duty cycles outside this range (with the exception of

100%), the shape of the expected fan-speed profile

varies too much between fans, and it is not possible to

predict an expected speed.

A fan-health-color bit in STATUS_FANS_1_2 is set based

upon the difference between the measured and expect-

ed fan speed and the FAN_HEALTH_CRITERIA bits in

MFR_MODE, as shown in Table 8. If the fan PWM duty

cycle is less than 40% or between 80% and 100%, a

fan-health color cannot be assigned and all the color

bits are cleared. If the fan is unstable, the YELLOW color

bit is set.

LOWER NIBBLE OF

STATUS_FAN_1_2

FAN_HEALTH_CRITERIA BITS IN

MFR_MODE

MONITORED FAN SPEED VS.

EXPECTED TARGET

GREEN

00 Within 10%

01 Within 10%

10 Within 15%

11 Within 15%

YELLOW — Fan speed is not stable

ORANGE

00 Between 10% and 15%

01 Between 10% and 20%

10 Between 15% and 20%

11 Between 15% and 25%

RED

00 Over 15%

01 Over 20%

10 Over 20%

11 Over 25%