Dual RPM-Based PWM Fan Controller
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.
100%
(optional)
30% through 65%
Fan Step
New Target Count
Algorithm controlled drive
Prev Target
Count = FFh
¼ of Spin Up Time
Update Time
Spin Up Time
Target Count
Reached
Check TACH
Target Count
Changed
Figure 4.2 Spin Up Routine
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.
Revision 1.1 (10-12-09)
SMSC EMC2302
DATA2S0HEET
SMSC [ SMSC CORPORATION ]
