FanControl

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DS-FanControl-TDA21801

4. General Description

The Fan Speed Controller is a fully integrated control with few external components to set up a flexible

and low cost application. The device uses the waveform of the current in a standard two-wire fan to

detect the speed of revolution and to control it.

The current flowing through the fan is sensed by the shunt resistor connected to RSin. For fans with a

supply current between 50mA and 400mA, a good value for this resistor is between 0.5 and 1Ω as the

maximum input voltage of RSin for linear operation is 330mV.

The Pulse Detector circuit creates one internal trigger pulse at every commutation of the fan motor. The

internal trigger pulse will be processed if the current waveform through the motor shows appropriate

variations at the commutation.

Monitoring and warning signal can be used to check the working condition.

Every two internal trigger pulses one is fed to the FanM output to monitor the speed of rotation.

The device controls the speed of revolution. The temperature is measured with the NTC thermistor and

according to the voltage on the NTC the speed of the fan is set.

In Fig.1 the dependence of the fan speed with the temperature is shown (supposing a minimum speed

of 1329 rpm).

The expression of the minimum VCO frequency @ minimum FAN Speed is given by:

P

n

fvco

*

*

15

16

=

P =number of pole (Fans in use for desktop PC SMPS are normally 4 poles).