RPM-Based Fan Controller with Multiple Temperature Zones & Hardware Thermal Shutdown
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.
100%
(optional)
30% through 65%
Fan Step
New Target Count
Algorithm controlled drive
Prev Target
Count = FFh
¼ of Spin Up Time
Spin Up Time
Update Time
Target Count
Reached
Check TACH
Target Count
Changed
Figure 6.4 Spin Up Routine
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".
Revision 1.2 (10-08-09)
SMSC EMC2113
DATA3S2HEET
SMSC [ SMSC CORPORATION ]
