RPM-Based Fan Controller with Multiple Temperature Zones & Hardware Thermal Shutdown
Datasheet
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 6.6, "RPM-Based Fan Speed Control Algorithm (FSC)"),
then the user must program a fan speed 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 PWM
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 channels, 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. Figure 6.3, "Fan Control Look-Up
Table Example" shows an example of this behavior using a single channel.
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.
To turn the fan off, there are 2 methods:
The first is to set the Temps1-4 Setting 1 values (+ hysteresis) above the temperatures desired for
the fan to turn off. When the temperatures fall below Temps1-4 (out of the LUT) by the hysteresis
amount, the fan drive will be set to 0.
The second is to set the Drive 1 value to 0% (or 0RPM) as well as the Temp 1-4 values to the
temperatures (+ hysteresis) at which the fan should turn off. This method will reduce the effective
amount of fan drive settings to 7.
Fan
Setting
Temp
T6
T6 - Hyst
S6
S5
T5
T5 - Hyst
T4
S4
T4 - Hyst
Averaged
Temperature
T3
S3
Fan
Setting
T3 - Hyst
S2
T2
T2 - Hyst
S1
Measurement taken
T1
Time
Figure 6.3 Fan Control Look-Up Table Example
Revision 1.2 (10-08-09)
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