Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown
Datasheet
to control the fan drive output independently (or jointly) by programming up to eight pairs of
temperature and drive setting entries.
The user programs the look-up table based on the desired operation. If the RPM based Fan Speed
Control Algorithm is to be used (see Section 5.5), then the user must program an RPM target for each
temperature setting of interest. Alternately, if the RPM based Fan Speed Control Algorithm is not to be
used, then the user must program a drive setting for each temperature setting of interest.
If the measured temperature on the External Diode channel meets or exceeds any of the temperature
thresholds for any of the temperature columns (see Appendix B), the fan output will be automatically
set to the desired setting corresponding to the exceeded temperature. In cases where multiple
temperature channel thresholds are exceeded, the highest fan drive setting will take precedence.
When the measured temperature drops to a point below a lower threshold minus the hysteresis value,
the fan output will be set to the corresponding lower set point.
Figure 5.3 shows an example of this operation using temperature - drive setting pairs for a single
channel.
See Appendix B for examples of the Look Up Table operation.
Fan
Setting
Temp
T8
T8 - Hyst
S8
S7
T7
T7 - Hyst
T6
S6
T6 - Hyst
T5
S5
T5 - Hyst
T4
S4
T4 - Hyst
Averaged
Temperature
T3
S3
S2
Fan
Setting
T3 - Hyst
T2
T2 - Hyst
S1
Measurement taken
T1
Time
Figure 5.3 Fan Control Look-Up Table Example
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Revision 1.74 (05-08-08)
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