MEC1322 Datasheet, PDF (298/456 Pages) Microchip Technology – Keyboard and Embedded Controller for Notebook PC

MEC1322
26.9.3 FAN CONFIGURATION 1 REGISTER
The Fan Configuration Register 1 controls the general operation of the RPM based Fan Control Algorithm used by the
fan driver.
Offset ^02h
Bits
Description
Type
7 EN_ALGO
R/W
Enables the RPM based Fan Control Algorithm.
• ‘0’ - (default) the control circuitry is disabled and the fan driver
output is determined by the Fan Driver Setting Register.
• ‘1’ - the control circuitry is enabled and the Fan Driver output will
be automatically updated to maintain the programmed fan
speed as indicated by the TACH Target Register.
6:5 RANGE[1:0]
R/W
Adjusts the range of reported and programmed tachometer reading
values. The RANGE bits determine the weighting of all TACH values
(including the Valid TACH Count, TACH Target, and TACH reading)
as shown in Table 26-9, "Range Decode".
4:3 EDGES[1:0]
R/W
Determines the minimum number of edges that must be detected on
the TACH signal to determine a single rotation. A typical fan mea-
sured 5 edges (for a 2-pole fan).
Increasing the number of edges measured with respect to the num-
ber of poles of the fan will cause the TACH Reading registers to indi-
cate a fan speed that is higher or lower than the actual speed. In
order for the FSC Algorithm to operate correctly, the TACH Target
must be updated by the user to accommodate this shift. The Effec-
tive Tach Multiplier shown in Table 26-10, "Minimum Edges for Fan
Rotation" is used as a direct multiplier term that is applied to the
Actual RPM to achieve the Reported RPM. It should only be applied
if the number of edges measured does not match the number of
edges expected based on the number of poles of the fan (which is
fixed for any given fan).
Contact Microchip for recommended settings when using fans with
more or less than 2 poles.
Default
0b
Reset
Event
VCC1_R
ESET
01b
VCC1_R
ESET
01b
VCC1_R
ESET
2:0 UPDATE[2:0]
R/W
Determines the base time between fan driver updates. The Update
Time, along with the Fan Step Register, is used to control the ramp
rate of the drive response to provide a cleaner transition of the actual
fan operation as the desired fan speed changes. The Update Time is
set as shown in Table 26-11, "Update Time".
APPLICATION NOTE: This ramp rate control applies for all
changes to the active PWM output
including when the RPM based Fan Speed
Control Algorithm is disabled.
011b
VCC1_R
ESET
DS00001719D-page 298
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