User guide

3.0 Application Notes
3.1 FAN CONTROL DUTY CYCLE VS. REGISTER SETTINGS AND FREQUENCY
PWM
Freq
4D
[4:0]
Step
Resolution,
%
PWM
Value
4D [5:0]
for 100%
PWM
Value
4C [5:0] for
about 75%
PWM
Value
4C [5:0]
for 50%
PWM
Freq at
360 kHz
Internal
Clock, kHz
PWM
Freq at
1.4 kHz
Internal
Clock, Hz
Actual Duty
Cycle, % When
75% is Selected
0 Address 0 is mapped to Address 1
1 50 2 1 1 180.0 703.1 50.0
2 25 4 3 2 90.00 351.6 75.0
3 16.7 6 5 3 60.00 234.4 83.3
4 12.5 8 6 4 45.00 175.8 75.0
5 10.0 10 8 5 36.00 140.6 80.0
6 8.33 12 9 6 30.00 117.2 75.0
7 7.14 14 11 7 25.71 100.4 78.6
8 6.25 16 12 8 22.50 87.9 75.0
9 5.56 18 14 9 20.00 78.1 77.8
10 5.00 20 15 10 18.00 70.3 75.0
11 4.54 22 17 11 16.36 63.9 77.27
12 4.16 24 18 12 15.00 58.6 75.00
13 3.85 26 20 13 13.85 54.1 76.92
14 3.57 28 21 14 12.86 50.2 75.00
15 3.33 30 23 15 12.00 46.9 76.67
16 3.13 32 24 16 11.25 43.9 75.00
17 2.94 34 26 17 10.59 41.4 76.47
18 2.78 36 27 18 10.00 39.1 75.00
19 2.63 38 29 19 9.47 37.0 76.32
20 2.50 40 30 20 9.00 35.2 75.00
21 2.38 42 32 21 8.57 33.5 76.19
22 2.27 44 33 22 8.18 32.0 75.00
23 2.17 46 35 23 7.82 30.6 76.09
24 2.08 48 36 24 7.50 29.3 75.00
25 2.00 50 38 25 7.20 28.1 76.00
26 1.92 52 39 26 6.92 27.0 75.00
27 1.85 54 41 27 6.67 26.0 75.93
28 1.79 56 42 28 6.42 25.1 75.00
29 1.72 58 44 29 6.21 24.2 75.86
30 1.67 60 45 30 6.00 23.4 75.00
31 1.61 62 47 31 5.81 22.7 75.81
3.1.1 Computing Duty Cycles for a Given Frequency
Select a PWM Frequency from the first column correspond-
ing to the desired actual frequency in columns 6 or 7. Note
the PWM Value for 100% Duty Cycle.
Find the Duty Cycle by taking the PWM Value of Register 4C
and computing:
Example: For a PWM Frequency of 24, a PWM Value at
100% = 48 and PWM Value actual = 28, then the Duty Cycle
is (28/48) x 100% = 58.3%.
LM63
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