Datasheet

12 V
2-
Temperature
sensor
AVSS
-wire Fan
Temperature
sensor
MONx
3
DC Fan
UCD90124A
GPIO
MOSFET turns
fan on and off
GPIO controls
MOSFET
GND
12 V
12 V
3-
Temperature
sensor
AVSS
-wire Fan
Fan Tach output to
GPI/GPIO for fan
speed monitoring
Temperature
sensor
MONx
GPIO
3
DC Fan
UCD90124A
GPIO
MOSFET turns
fan on and off
GPIO controls
MOSFET
GND
12 V
TACH
UCD90124A
SLVSAN8 –JANUARY 2012 www.ti.com
voltage for the fan. The negative input of the fan is connected to the collector or drain of a transistor. The
transistor is turned off and on using a GPIO pin. Four-wire fans can be controlled the same way. However,
four-wire fans should use the fan PWM input (the fourth wire). It can be driven directly by one of the eight FPWM
or the two adjustable PWM outputs. The normal frequency range for the PWM input is 15 kHz to 40 kHz, but the
specifications for the fan confirm the interface procedure.
Figure 23. Two-Wire Fan Connection
Figure 24. Three-Wire Fan Connection
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