SMSC EMC2102 Manual do Utilizador descarregar pdf (Página 31)

Fan Speed Control with the EMC2102 Device

SMSC EMC2102

USER MANUAL Revision 0.2 (09-17-07)

5.7.1.3 Case 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".

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.

Figure 5.28 Spin-up Case 2

Figure 5.29 Theoretical Plot of Case 3

Fan Drive Setting (51h)

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

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SMSC EMC2102 Manual do Utilizador Página 31