EMC2302 datasheet(20/44 Pages) SMSC

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Dual RPM-Based PWM Fan Controller

Datasheet

Revision 1.1 (10-12-09)

SMSC EMC2302

DATASHEET

After the Spin Up Routine has finished, the EMC2302 measures the TACHx signal. If the measured

TACH Reading Register value is higher than the Valid TACH Count Register setting, the FAN_SPIN

status bit is set and the Spin Up Routine will automatically attempt to restart the fan.

Figure 4.2 shows an example of the Spin Up Routine in response to a programmed fan speed change

based on the first condition above.

4.7

Ramp Rate Control

The Fan Driver can be configured with automatic ramp rate control. Ramp rate control is accomplished

by adjusting the drive output settings based on the Maximum Fan Step Register settings and the

Update Time settings.

If the RPM-based Fan Speed Control Algorithm is used, then this ramp rate control is automatically

used. The user programs a maximum step size for the fan drive setting and an update time. The

update time varies from 100ms to 1.6s while the fan drive maximum step can vary from 1 count to 31

counts.

When a new fan drive setting is entered, the delta from the next fan drive setting and the previous fan

drive setting is determined. If this delta is greater than the Max Step settings, then the fan drive setting

is incrementally adjusted every 100ms to 1.6s as determined by the Update Time until the target fan

drive setting is reached. See Figure 4.3.

Figure 4.2 Spin Up Routine

100%

(optional)

30% through 65%

Algorithm controlled drive

Fan Step

Spin Up Time

¼ of Spin Up Time

Update Time

Target Count

Changed

Target Count

Reached

New Target Count

Prev Target

Count = FFh

Check TACH

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