Philips Semiconductors

Product data

P82CF201

Low power, low price dual fan manager

2002 Nov 18

4

su01718

COMPARATOR

Figure 2.

Fan Drive

Depending on the value of the thermistor, the fans will be driven by

MOSFET with a PWM signal.

When the thermistor resistance is higher than 10 K

Ω and

THRESHOLD is set to “0” , the fan will be turned off.

However when the thermistor resistance is higher than 10 K

Ω and

THRESHOLD is set to “0” , the fan will be driven by a 30% duty

cycle.

When the thermistor resistance is 10 K

Ω, the fan will be driven by a

30% duty cycle PWM signal.

When the thermistor resistance is 1.7 K

Ω, the fan will be driven by a

95% duty cycle PWM signal.

Any value in between is linear.

A Hysteresis with 30% PWM duty cycle (when THRESHOLD = 0) is

introduced to maintain constant cooling when the thermistor cools

from 10K (approx. 25

°C) to down 15K (approx. 20 °C). This reduces

on/off cycling for small temperature fluctuation.

When THRESHOLD is not connected or tied to “1”, the fans will

have a 30% PWM duty cycle to maintain constant cooling whenever

power is applied.

amplifier (for N-type MOSFet) is needed. For easy reference, this

circuit is shown in Figure 5.

su01719

30%

95%

98%

PWM

1.7K

10K

15K

HYSTERESIS

(THRESHOLD = 0)

Figure 3.