Fan Speed Control with the EMC2102 Device
Fan Drive Setting (51h)
Figure 5.28 Spin-up Case 2
5.7.1.3Case 3 - Valid RPM =< Target RPM << Spin-up Level RPM
In this case, the target speed is only a little greater than the valid speed, and both of them are much smaller than the spin-up level speed (rpm60 or rpm75). The theoretical plot of this situation is shown in Figure 5.29, "Theoretical Plot of Case 3".
Fan Speed
(RPM)RPM for
100% Drive
rpm60 or rpm75
Fan Speed
Target Speed
Valid Speed
¼of Spin Up Time
Spin Up Time
Check TACH
Figure 5.29 Theoretical Plot of Case 3
Since the fan speed at the end of spin-up routine is higher than the minimum valid speed, the EMC2102 should go to the normal operation after the spin-up routine. However, because the large speed difference between the spin-up level speed (rpm60 or rpm75) and the target speed, the closed- loop controller will try to make a big adjustment of its output to reach the target speed. With incorrect settings (such as big output step or short update time), this adjustment could easily cause an undershoot and make the fan speed below the valid rpm, and than make the spin-up routine restart.
SMSC EMC2102 | USER MANUAL | Revision 0.2 (09-17-07) |