EMC2113 datasheet(32/85 Pages) SMSC

32 / 85 page

RPM-Based Fan Controller with Multiple Temperature Zones & Hardware Thermal Shutdown

Datasheet

Revision 1.2 (10-08-09)

SMSC EMC2113

DATASHEET

When the Spin Up Routine is operating, the fan driver is set to full scale (optional) for one quarter of

the total user defined spin up time. For the remaining spin up time, the fan driver output is set to a

user defined level (30% through 65% drive).

After the Spin Up Routine has finished, the EMC2113 measures the TACH 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 6.4, "Spin Up Routine" shows an example of the Spin Up Routine in response to a programmed

fan speed change based on the first condition above.

6.9

Ramp Rate Control

The PWM output drive can be configured with automatic ramp rate control. If the RPM-based Fan

Speed Control Algorithm is used, then this ramp rate control is automatically used based on the fan

control derivative option settings. The user programs a maximum step size for the PWM setting and

an update time. The update time varies from 100ms to 1.6s while the PWM maximum step can vary

from 1 PWM count to 31 PWM counts.

When a new PWM duty cycle value is entered (either directly, as a result of the FSC Algorithm

adjusting the output PWM to meet the programmed TACH Target value, or as a result of the ramp rate

control circuitry), the delta from the next PWM and the previous PWM is determined. If this delta is

greater than the maximum fan step settings, then the PWM is adjusted by the maximum fan step

settings.

The PWM duty cycle is adjusted (and the delta recalculated) every 100ms to 1.6s as determined by

the Update Time until the target PWM setting is reached. See Figure 6.5, "Ramp Rate Control".

Figure 6.4 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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