0 application notes, 1 computing duty cycles for a given frequency – Rainbow Electronics LM63 User Manual
Page 24
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%.
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