%

100

%

100

_

_

_

_

_(%)

u

=

for

Value

PWM

Value

PWM

DutyCycle

LM63

www.ti.com

SNAS190E – SEPTEMBER 2002 – REVISED MAY 2013

APPLICATION NOTES

FAN CONTROL DUTY CYCLE VS. REGISTER SETTINGS AND FREQUENCY

ACTUAL

PWM

PWM

PWM

PWM

PWM

DUTY

PWM

STEP

FREQ AT

FREQ AT

VALUE

VALUE

VALUE

CYCLE, %

FREQ

RESOLUTION,

360 kHz

1.4 kHz

4D [5:0]

4C [5:0] FOR

4C [5:0]

WHEN

4D [4:0]

%

INTERNAL

INTERNAL

FOR 100%

ABOUT 75%

FOR 50%

75% IS

CLOCK, kHz

CLOCK, Hz

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

COMPUTING DUTY CYCLES FOR A GIVEN FREQUENCY

Select a PWM Frequency from the first column corresponding 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:

(1)

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) × 100% = 58.3%.

Copyright © 2002–2013, Texas Instruments Incorporated

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