EMC2302 datasheet(35/44 Pages) SMSC

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Dual RPM-Based PWM Fan Controller

Datasheet

SMSC EMC2302

Revision 1.1 (10-12-09)

DATASHEET

5.13

Fan Max Step Registers

The Fan Max Step registers, along with the Update Time, control the ramp rate of the fan driver

response calculated by the RPM-based Fan Speed Control Algorithm. The value of the register

represents the maximum step size each fan driver will take between update times (see Section 5.9).

When the FSC algorithm is enabled, Ramp Rate control is automatically used. When the FSC is not

active, then Ramp Rate control can be enabled by asserting the EN_RRC bit (see Section 5.10).

APPLICATION NOTE: The UPDATE bits and Fan Step Register settings operate independently of the RPM-based

Fan Speed Control Algorithm and will always limit the fan drive setting. That is, if the

programmed fan drive setting (either as determined by the RPM-based Fan Speed Control

Algorithm or by manual settings) exceeds the current fan drive setting by greater than the

Fan Step Register setting, the EMC2302 will limit the fan drive change to the value of the

Fan Step Register. It will use the Update Time to determine how often to update the drive

settings.

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

The Fan Max Step registers are software locked.

Table 5.22 Spin Time

SPINUP_TIMEX[1:0]

TOTAL SPIN UP TIME

250 ms

500 ms (default)

1 sec

2 sec

Table 5.23 Fan Max Step Registers

ADDR

R/W

DEFAULT

37h

R/W

Fan 1 Max

Step

10h

47h

R/W

Fan 2 Max

Step

10h

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