LM64EVAL National Semiconductor, LM64EVAL Datasheet - Page 25

• Manufacturer Part Number: LM64EVAL
• Description: BOARD EVALUATION LM64
• Manufacturer: National Semiconductor

Specifications of LM64EVAL

• Sensor Type: Temperature, Fan Controller
• Sensing Range: 0°C ~ 85°C
• Interface: SMBus (2-Wire/I²C)
• Sensitivity: ±1°C
• Voltage - Supply: 3 V ~ 3.6 V
• Embedded: Yes, MCU, 8-Bit
• Utilized Ic / Part: LM64
• Lead Free Status / RoHS Status: Not applicable / Not applicable

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