Description
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5.10 Fan Interface
The UCD90124 provides support for up to four fans. The UCD90124EVM provides a single fan interface
from J66. The UCD90124EVM interface can support three fan types including 2-wire, 3-wire, and 4-wire.
The FAN connector has four terminals (12V, GND, Tach, and PWM).
5.10.1
Fan Tach Input
The fan tach signal is an input to the UCD90124 providing an indication of fan speed based on signal
frequency. The EVM Tach input signal is conditioned prior to being connected to the UCD90124 and can
interface with either a 3.3V or 5V signal using J72. Install a shunt in the TACH position of J67 to connect
the conditioned signal to the UCD90124. The TACH signal at J66-2 is inverted by the conditioning circuitry
prior to J67.
5.10.2
Fan PWM Output
The fan PWM signal is an output from the UCD90124 providing fan speed control using a pulse width
modulated signal. The UCD90124 output signal can come from either PWM1 (J67 in the PWM position) or
FPWM5 (J70 in the FPWM5 position). The PWM1 or FPWM5 output signal can directly drive the fan PWM
input (four wire fan with J68 in the 4W position) or be conditioned prior the fan PWM input (two or three
wire fan with J68 in the 2/3W position). When J68 is in the 2/3W position, the PWM signal at J66-3 can
drive or modulate the ground of a two or three wire fan. When J68 is in the 2/3W position, the PWM signal
at J66-3 can provide a 3.3V, 5V, or 12V level PWM signal with appropriately installed shunts on J69 for
use with four wire fans. When J68 is in the 2/3W position, the PWM1 or FPWM5 signal at J70 is inverted
by the conditioning circuitry prior to J66-3.
5.10.3
Fan Temperature Simulation
An onboard potentiometer (TEMP MON) can be used to simulate analog temperature when used in
conjunction with the fan interface for fan speed control. The potentiometer voltage can be monitored at
TP54 (TEMP MON) through MON12. Install a shunt in the 12E position of J61 and install J71 (EVR12).
The potentiometer voltage can be varied from 0 to approximately 4.2V. This voltage is scaled by 2 before
being sampled at MON12.
30
Evaluation Module for UCD90120 and UCD90124
SLVU347 – December 2009
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