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Fan Speed Control with the EMC2102 Device
SMSC EMC2102
USER MANUAL Revision 0.2 (09-17-07)
33
5.7.1.4 Case 4 - 4.Valid RPM < Spin-up Level RPM (rpm60 or rpm75) < Target RPM
In this case, the spin-up level speed (rpm60 or rpm75) is greater than the valid speed and smaller than
the target speed, as shown in Figure 5.32, "Theoretical Plot of Case 4".
At the end of spin-up routine, the closed-loop control will drive the fan up to reach the target, therefore
the fan speed will never be lower than the valid speed. The EMC2102 will go to the normal operation
after the spin-up routine.
Using the EVB-EMC2102 to test this situation with rpm60 (~4500 rpm), simply set the Valid TACH
register (56h) with 3500 rpm and start the fan with TACH Target (57h) = 5000 rpm (Figure 5.33, "Spin-
up Case 4").
Figure 5.32 Theoretical Plot of Case 4
Figure 5.33 Spin-up Case 4
RPM for
100% Drive
rpm60 or rpm75
Spin Up Time
¼ of Spin Up Time
Valid Speed
Check TACH
Fan Speed
(RPM)
Target Speed
Fan Speed