SMSC EMC2102 - Manual (Page 30)

Fan Speed Control with the EMC2102 Device
Revision 0.2 (09-17-07)
USER MANUAL
SMSC EMC2102
30
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