MEC1322 datasheet(298/456 Pages) MICROCHIP

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MEC1322

DS00001719D-page 298

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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

Default

Reset

Event

7EN_ALGO

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.

R/W

VCC1_R

ESET

6:5 RANGE[1:0]

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".

R/W

01b

VCC1_R

ESET

4:3 EDGES[1:0]

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.

R/W

01b

VCC1_R

ESET

2:0 UPDATE[2:0]

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.

R/W

011b

VCC1_R

ESET

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