EMC2103 datasheet(63/85 Pages) MICROCHIP

63 / 85 page

RPM-Based Fan Controller with Hardware Thermal Shutdown

Datasheet

 2013 Microchip Technology Inc.

DS0005250A-page 63

6.26

Fan Step Register

The Fan Step Register, along with the Update Time, control the ramp rate of the fan driver response.

The value of the registers represents the maximum step size each fan driver will take between update

times (see Section 6.22).

All modes of operation have the options to use the Fan Step Register (and update times) for ramp rate

control based on the Fan Configuration 2 Register settings. The Fan Speed Control Algorithm will

always use the Fan Step Register settings (but see application note below).

APPLICATION NOTE: If the Fan Speed Control Algorithm is used, the default settings in the Fan Configuration 2

The Fan Step Register is software locked.

6.27

Fan Minimum Drive Register

The Fan Minimum Drive Register stores the minimum drive setting for the RPM based Fan Speed

Control Algorithm. This register is not used if the FSC is not active. The RPM based Fan Speed Control

Algorithm will not drive the fan at a level lower than the minimum drive unless the target TACH Target

is set at FFh (see Section 6.30)

During normal operation, if the fan stops for any reason (including low drive), the RPM based Fan

Speed Control Algorithm will attempt to restart the fan. Setting the Fan Minimum Drive Registers to a

setting that will maintain fan operation is a useful way to avoid potential fan oscillations as the control

circuitry attempts to drive it at a level that cannot support fan operation.

The Fan Minimum Drive Register is software locked.

6.28

Valid TACH Count Register

The Valid TACH Count Register store the maximum TACH Reading Register value to indicate that the

the fan is spinning properly. The value is referenced at the end of the Spin Up Routine to determine

if the fan has started operating and decide if the device needs to retry.

Table 6.43 Fan Step Register

ADDR

R/W

DEFAULT

47h

R/W

Fan Max Step

10h

Table 6.44 Minimum Fan Drive Register

ADDR

R/W

DEFAULT

48h

R/W

Fan Minimum

Drive

128

8421

66h

(40%)

Table 6.45 Valid TACH Count Register

ADDR

R/W

DEFAULT

49h

R/W

Valid TACH

Count

4096

2048

1024

512

256

128

F5h

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