MAX31785ETL+ Maxim Integrated Products, MAX31785ETL+ Datasheet - Page 25

• Manufacturer Part Number: MAX31785ETL+
• Description: Board Mount Temperature Sensors 6Ch Intelligent Fan Controller
• Manufacturer: Maxim Integrated Products

Specifications of MAX31785ETL+

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Multiple fans are not started at the same time. Fans are
started in increments of 200ms to relieve the strain on the
power supply. This sequencing occurs both at initial fan
power-up and when fans are turned off and on during
normal operation.
The device has a fan-health-diagnostic function to help
predict the remaining life of the fan. This function com-
pares the measured vs. expected fan speed for the
applied PWM duty cycle to determine if the fan is operat-
ing normally. This function is enabled with the HEALTH bit
(bit 4) in MFR_FAN_CONFIG. When the fan-health-meter
Figure 4. Fan PWM to RPM Example
RPM@100% PWM
RPM@60% PWM
RPM@60% PWM
RPM@40% PWM
EXPECTED FAN
SPEED IN RPM
Fan Health-Meter Function
Fan Power-On Sequencing
6-Channel Intelligent Fan Controller
20
EXPECTED FAN PWM
TO SPEED PROFILE
40
PWM DUTY CYCLE (%)
function is enabled, it runs once per second for each
enabled fan. If the fan’s PWM duty cycle has been stable
for 30s, the measured RPM is compared to the expect-
ed RPM and the correct fan-health-color bit (GREEN,
ORANGE, or RED) is set in STATUS_FAN_1_2. If the duty
cycle has been unstable for greater than 10 minutes, the
YELLOW bit is set in STATUS_FANS_1_2.
The expected fan-speed profile is entered with the
MFR_FAN_PWM2RPM command. With this command,
a table is filled with four preassigned PWM duty cycle
(40%, 60%, 80%, and 100%) vs. expected fan-speed
values, as shown in Figure 4. The comparison of the
measured RPM to expected RPM is performed when the
60
80
100
RED
ORANGE
GREEN
GREEN
ORANGE
RED
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