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Figure 5.32 theoretical plot of case 4, Figure 5.33 spin-up case 4, User manual – SMSC EMC2102 User Manual

Page 33

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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