MEC1322 Datasheet, PDF (293/456 Pages) Microchip Technology – Keyboard and Embedded Controller for Notebook PC

FIGURE 26-2:
RPM BASED FAN CONTROL ALGORITHM
Set TACH Target
Count
MEC1322
Measure Fan Speed
Spin Up
Yes
Required
?
No
Perform Spin Up
Routine
Yes
Maintain Fan Drive
Yes
TACH
Reading=
TACH
Target?
No
TACH
Reading <
No
TACH
Target?
Ramp Rate Control
Reduce Fan Drive
Increase Fan Drive
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.
1. Set the Valid TACH Count Register to the minimum tachometer count that indicates the fan is spinning.
2. Set the Spin Up Configuration Register to the spin up level and Spin Time desired.
3. Set the Fan Step Register to the desired step size.
4. Set the Fan Minimum Drive Register to the minimum drive value that will maintain fan operation.
5. Set the Update Time, and Edges options in the Fan Configuration Register.
6. Set the TACH Target Register to the desired tachometer count.
7. Enable the RPM based Fan Control Algorithm by setting the EN_ALGO bit.
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DS00001719D-page 293