LM93 datasheet(37/95 Pages) TI1

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LM93

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SNAS210E – DECEMBER 2003 – REVISED MARCH 2013

Table 3-3. Zone 3/4 (LM93 Ambient and External Ambient) Table(1)

Lookup Table

Zone 3/4

Tbase

LM93 Ambient, Zone 3 (TA)

Tbase

External Ambient, Zone 4 (TA)

Duty Cycle

Toffset

LM93

External

table

Ambient

(%)

(°C)

TA<

31.25

37.5

43.75

56.25

62.5

≤TA<

68.75

≤TA<

81.25

0.5

≤TA<

33.5

≤TA<

38.5

87.5

0.5

33.5

≤TA<

38.5

≤TA<

93.75

0.5

≤TA<

34.5

≤TA<

39.5

100

34.5

≤TA

39.5

≤TA

(1)

In this example: Zone 3 and Zone 4 are bound to the PWM 2 output and the PWM2 output frequency set to 22.5kHz; Hysteresis is set to

1°C; Toffset and hysteresis resolution set to 0.5°C; minPWM for Zones 3/4 register is set to 06h. Note, the duty cycle assignment

depends on the zone to PWM output binding and the frequency setting of that PWM output.

3.16.10.2 Fan Control Temperature Resolution

As shown in the example the auto fan control algorithm can operate in a mode that allows 0.5°C of

temperature resolution instead of the normal 1°C. When this mode is enabled, the temperature offset

registers that make up the lookup table are interpreted differently. One LSB represents 0.5°C, and the

available range between each datapoint is 0°C to 7.5°C instead of 0°C to 15°C. In addition, the hysteresis

registers for auto fan control are interpreted in the same way (one LSB equals 0.5°C).

Zones 1, 2 and 3 all have 9-bits of internal resolution, which makes this feature useful. Zone 4 is written in

from the SMBus and only has 8-bits of resolution. The LM93 left justifies the value into a 9-bit field before

using it, if the 0.5°C mode is enabled.

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.

3.16.10.3 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.

3.16.10.4 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 associates 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) frequency.

Functional Description

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