2002 Microchip Technology Inc. DS21506B-page 5
TC652 Fan Control Demo Board
User’s Guide
Chapter 2. Getting Started
This chapter describes the TC652 Demo Board’s configuration and how it functions. It
also provides information on typical fan demo board operating configurations for fan
applications.
The board is equipped with a TC652AEVUA device, which features a minimum
temperature limit (T
L
) of 25°C (40% duty cycle) and a maximum temperature limit
(T
H
) of 45°C (100% duty cycle).
2.1 TC652 FUNCTIONAL DESCRIPTION
2.1.1 PWM Output
The pulse width modulation (PWM) pin is designed to drive a low cost transistor or
MOSFET as the low side power switching element in the system. A 2N2222 type, small
signal (BJT) can be used for fans up to 300 mA. For larger current fans (up to 1 amp),
a logic-level N-channel MOSFET must be used. Since the system relies on pulse width
modulation, rather than linear power control, the dissipation in the power switch is kept
to a minimum. Generally, very small devices, such as the TO-92 or SOT, will suffice.
Test Point TP1 can be connected to an oscilloscope for observing PWM output
characteristics.
2.1.2 SHDN
The fan can be unconditionally shut down by pulling the SHDN pin low. This function
can be implemented by removing jumper JP
1
, and then grounding pin 3. For details see
Figure A-2, in the Appendix A section.
2.1.3 FAULT
During normal fan operation, commutation occurs as each pole of the fan is ener-
gized. This causes brief interruptions in the fan current, seen as pulses across the
sense resistor R3. If the device is not in shutdown or auto-shutdown (TC653), and
pulses are not appearing at the SENSE input, a fault exists. In this case, the LED1
light turns on to indicate the fan failure.
2.1.4 SENSE Input
The sense network, comprised by R
SENSE
and C
SENSE
, allows the TC652/TC653 to
detect and monitor commutation of the fan motor (and therefore fan operation). A 0.01 µF
capacitor is recommended for C
SENSE
(C
2
). The TC652 Demo Board is populated with a
4.7Ω current sense resistor (R
SENSE
). This resistor value should be scaled based on the
current rating of the fan. This resistor is socketed on the demo board to allow for easy
value changes (see Table 2-1 for resistor value selections).
