MEC1322 datasheet(293/456 Pages) MICROCHIP

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DS00001719D-page 293

MEC1322

FIGURE 26-2:

RPM BASED FAN CONTROL ALGORITHM

26.8.3.1

Programming the RPM Based Fan Control Algorithm

The RPM based Fan Control Algorithm powers-up disabled. The following registers control the algorithm. The RPM-

PWM Interface fan control registers are pre-loaded with defaults that will work for a wide variety of fans so only the TACH

Target Register is required to set a fan speed. The other fan control registers can be used to fine-tune the algorithm

behavior based on application requirements.

Set the Valid TACH Count Register to the minimum tachometer count that indicates the fan is spinning.

Set the Spin Up Configuration Register to the spin up level and Spin Time desired.

Set the Fan Step Register to the desired step size.

Set the Fan Minimum Drive Register to the minimum drive value that will maintain fan operation.

Set the Update Time, and Edges options in the Fan Configuration Register.

Set the TACH Target Register to the desired tachometer count.

Enable the RPM based Fan Control Algorithm by setting the EN_ALGO bit.

Set TACH Target

Count

Measure Fan Speed

Perform Spin Up

Routine

Maintain Fan Drive

Ramp Rate Control

Reduce Fan Drive

Increase Fan Drive

Spin Up

Required

TACH

Reading=

TACH

Target?

TACH

Reading <

TACH

Target?

Yes

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