MEC1322 Datasheet, PDF (292/456 Pages) Microchip Technology – Keyboard and Embedded Controller for Notebook PC

MEC1322
2. Using RPM based Fan Control Algorithm - in this mode of operation, the user determines a target tachometer
reading and the drive setting is automatically updated to achieve this target speed.
TABLE 26-6: FAN CONTROLS ACTIVE FOR OPERATING MODE
Manual Mode
Algorithm
Fan Driver Setting (read / write)
EDGES[1:0] (Fan Configuration)
UPDATE[2:0] (Fan configuration)
LEVEL (Spin Up Configuration)
SPINUP_TIME[1:0] (Spin Up Configuration)
Fan Step
-
Valid TACH Count
-
TACH Reading
RANGE[2:0] (Fan Configuration 2)
-
Fan Driver Setting (read only)
EDGES[1:0] (Fan Configuration)
UPDATE[2:0] (Fan configuration)
LEVEL (Spin Up Configuration)
SPINUP_TIME[1:0] (Spin Up Configuration)
Fan Step
Fan Minimum Drive
Valid TACH Count
TACH Target
TACH Reading
RANGE[2:0] (Fan Configuration 2)
DRIVE_FAIL_CNT[2:0] (Spin Up Config) and
Drive Fail Band
26.8.3 RPM BASED FAN CONTROL ALGORITHM
The RPM-PWM Interface includes an RPM based Fan Control Algorithm.
The fan control algorithm uses Proportional, Integral, and Derivative terms to automatically approach and maintain the
system’s desired fan speed to an accuracy directly proportional to the accuracy of the clock source. Figure 26-2, "RPM
based Fan Control Algorithm" shows a simple flow diagram of the RPM based Fan Control Algorithm operation.
The desired tachometer count is set by the user inputting the desired number of 32.768KHz cycles that occur per fan
revolution. The user may change the target count at any time. The user may also set the target count to FFh in order to
disable the fan driver.
For example, if a desired RPM rate for a 2-pole fan is 3000 RPMs, the user would input the hexadecimal equivalent of
1312d (52_00h in the TACH Target Registers). This number represents the number of 32.768KHz cycles that would
occur during the time it takes the fan to complete a single revolution when it is spinning at 3000RPMs (see Section
26.9.11, "TACH Target Register" and Section 26.9.12, "TACH Reading Register").
The RPM-PWM Interface’s RPM based Fan Control Algorithm has programmable configuration settings for parameters
such as ramp-rate control and spin up conditions. The fan driver automatically detects and attempts to alleviate a
stalled/stuck fan condition while also asserting the interrupt signal. The RPM-PWM Interface works with fans that oper-
ate up to 16,000 RPMs and provide a valid tachometer signal. The fan controller will function either with an externally
supplied 32.768KHz clock source or with its own internal 32KHz oscillator depending on the required accuracy.
DS00001719D-page 292
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