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Fan Speed Control with the EMC2102 Device
Revision 0.2 (09-17-07)
USER MANUAL SMSC EMC2102
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5.7.1.2 Case 2 - Valid RPM << Target RPM < Spin-up Level RPM
In this case, the target speed is smaller than the spin-up level speed (rpm60 or rpm75) and is much
bigger than the valid speed. The theoretical plot of this situation is shown in Figure 5.27, "Theoretical
Plot of Case 2".
Since the fan speed at the end of spin-up routine is always higher than the minimum valid speed, the
EMC2102 will go to the normal operation after the spin-up routine.
Using the EVB-EMC2102 to test this situation with rpm75 (~5650 rpm), simply set the Valid TACH
register (56h) with 4500 rpm and start the fan with TACH Target (57h) = 5500 rpm (Figure 5.28, "Spin-
up Case 2").
Figure 5.26 Spin-up Case 1 Fix 2
Figure 5.27 Theoretical Plot of Case 2
Fan Drive Setting (51h)
Valid Speed = 5800 rpm
Valid Speed = 5580 rpm
Valid Speed = 6000 rpm
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