LM93 datasheet(31/92 Pages) NSC

31 / 92 page

15.0 Using The LM93 (Continued)

Note that since zones 1 and 2 share the same lookup table,

both zones must be operating in the same resolution mode.

The same applies to zones 3 and 4 since they share the

same lookup table.

15.10.3 Zone 1-4 to PWM1-2 Binding

Each zone must be bound to the PWM outputs in order to

have effect on the output’s duty cycle. Any combination of

the zones may be used to drive a PWM output, they are not

limited to the binding described in the previous example. For

instance zones 1, 2 and 4 may be bound to PWM1 while

zones 3 and 4 are bound to PWM2. Note that the duty cycle

levels in the lookup table are dependent on the PWM output

frequency assignment. Therefore, if PWM1 is assigned to a

high frequency and PWM2 is assigned to a low frequency, in

the binding example just mentioned, zone 4 has a different

duty cycle calculated through the lookup table for PWM1

than for PWM2, even though the same Toffset values are

used. This is due to the fact that PWM levels assigned to a

high frequency PWM output are different than the levels

assigned to a low frequency PWM output.

15.10.4 Fan Control Duty Cycles

Several registers in the LM93 use 4-bit values to represent a

duty cycle. All of them use a common mapping that associ-

ates the 4-bit value with a duty cycle. The 4-bit values

correspond also with the 14 steps of the auto fan control

algorithm. The mapping is shown below. This applies for

PWM outputs running at the default 22.5 kHz (high) fre-

quency.

4-Bit Value

Step

22.5 kHz (High Frequency)

Duty Cycle

0.00%

25.00%

31.25%

37.50%

43.75%

50.00%

56.25%

62.50%

68.75%

75.00%

81.25%

87.50%

93.75%

100.00%

—

Reserved

—

Reserved

15.10.5 Alternate PWM Frequencies

The PWM output can operate at lower frequencies, instead

of the default 22.5 kHz. The alternate lower frequencies can

be enabled through the PWMx Control 4 registers. When

operating in the lower frequency mode, the mapping be-

tween step numbers and duty cycles changes. This effects

the auto fan control and all LM93 registers that describe a

duty cycle using a 4-bit value.

The low frequency PWM output duty cycle mapping is listed

in the following table:

4-Bit Value

Step

Low Frequencies

Duty Cycle

25.00%

28.57%

32.14%

35.71%

39.29%

42.86%

46.43%

50.00%

53.57%

57.14%

71.43%

85.71%

100.00%

—

Reserved

—

Reserved

15.10.6 Fan Control Priorities

The automatic fan control is not the only function that influ-

ences PWM duty cycle. There are several other functions

that influence the PWM duty cycle. All the functions can be

classified into several categories:

LM93 Datasheet(PDF) 31 Page - National Semiconductor (TI)

LM93 Datasheet(HTML) 31 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92

Datasheet Download

Link URL