Functional Description (Continued)
DS100040-12
(a) Fan with Tach Pull-Up to +5V
DS100040-13
(b) Fan with Tach Pull-Up to +12V, or Totem-Pole
Output and Resistor Attenuator
DS100040-14
DS100040-15
(c) Fan with Tach Pull-Up to +12V and Diode Clamp
(d) Fan with Strong Tach Pull-Up or Totem Pole Output
and Diode Clamp
FIGURE 7. Alternatives for Fan Inputs
Counts are based on 2 pulses per revolution tachometer outputs.
RPM
Time per Revolution
Counts for “Divide by 2”
(Default) in Decimal
153 counts
Comments
4400
3080
2640
13.64 ms
19.48 ms
22.73 ms
Typical RPM
70% RPM
60% RPM
219 counts
255 counts
(maximum counts)
Nominal
Counts for the
70%
Time per Revolution
Mode Select
Time per Revolution
RPM
RPM
Given Speed in Decimal
for 70% RPM
9.74 ms
Divide by 1
Divide by 2
Divide by 4
Divide by 8
8800
4400
2200
1100
6.82 ms
13.64 ms
27.27 ms
54.54 ms
153
153
153
153
6160
3080
1540
770
19.48 ms
38.96 ms
77.92 ms
15
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