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Fan Speed Control with the EMC2102 Device
Revision 0.2 (09-17-07)
USER MANUAL SMSC EMC2102
28
5.7 Experiment 7 - Troubleshooting
5.7.1 Repetitious Spin-up Routine Caused by Incorrect Settings
At the end of spin-up routine (see Section 5.3.1, "Fan Control Parameters"), the EMC2102 checks the
TACH Reading register (58h). If the value in this register is greater than the Valid TACH Count (56h),
which means the fan is running at a speed slower than the minimum valid speed, the spin-up routine
will be restarted (Figure 5.23, "Fan Spin-up Routine Restarted Repeatedly").
Depending on the fan characters and EMC2102 settings, there are several situations at the end of
spin-up routine which will be discussed.
Notes: For ease of understanding, all TACH values will be converted to RPM values in the following
examples.
5.7.1.1 Case 1 - Spin-up Lvel RPM < Valid RPM < Target RPM
In this case, the spin-up level rpm (rpm60 or rpm75) is smaller than both valid rpm (function of 56h)
and target rpm (function of 57h). The theoretical plot of this situation is shown in Figure 5.24,
"Theoretical Plot of Case 1".
Since the fan speed at the end of spin-up routine is always below the minimum valid speed (a function
of 56h), the EMC2102 will think the fan is not running, and will try to restart the fan with spin-up routine
over and over.
Using the EVB-EMC2102 to test this situation with rpm60 (~4500 rpm), simply set the Valid TACH
register (56h) with 4800 rpm and start the fan with TACH Target (57h) = 5000 rpm. The repeating spin-
up routines can be observed (Figure 5.25, "Spin-up Case 1 Fix 1").
For rpm75 (~5650 rpm), set 56h = 6000 rpm and 57h = 6500 rpm, as shown in Figure 5.26, "Spin-up
Case 1 Fix 2".
There are mainly two ways to fix this problem. If the spin-up LEVEL in 53h is 60%, then change it to
75%, as shown in Figure 5.25.
Figure 5.23 Fan Spin-up Routine Restarted Repeatedly