P82CF201 datasheet(5/11 Pages) PHILIPS

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Philips Semiconductors

Product data

P82CF201

Low power, low price dual fan manager

2002 Nov 18

Motor Failure Detection and fault Reporting

(including watchdog reset)

As shown in Figure 4, the VSENSE input is connected to the collector

of NPN transistor through an inverting buffer transistor (2N3904 or

PMBT3904D) which amplifies the signal from the low-value current

sensing resistor in the ground return leg of the fan circuit. During

normal fan operation, communication occurs as each pole of the fan

is energized.

The fan current develops across the sense resistor(RSENSE). This a

voltage follower of the PWM pin.

In a running motor, a current will flow through the resistor RSENSE

resulting in a voltage drop. The commutation will cause a narrow

window where there is no current flow. Motor detection is done by

the presence of commutation pulses. If there is constant voltage

level on the VSENSE pin when the motor is driven by a PWM signal,

the motor is jammed. When there is no voltage at all, the motor

might not be connected or the MOSFET is defective. The fault

condition also triggers the maximum PWM applied to the running

fan.

To detect the commutation pulses correctly, the VSENSE input needs

a logic high level of 0.2*VDD+0.9 V. (For example:

1.56 V@VDD=3.3 V). The design of proper sense circuitry is a

matter of scaling the RSENSE and the gain in buffer transistor to

meet the logic high as shown in Figure 4. Assuming the VBE(min) of

the transistor is approx. 0.5 V. Table 1 lists some recommended

RSENSE values according to the nominal operating current.

Table 1. Recommended values of RSENSE per

Figure 4

Nominal Fan Current(mA)

Min RSENSE(ohms)

100

5.1

200

2.5

450

2.2

800

1.0

In addition, when the thermistor resistance falls below 1.7 K

Ω (for

NTC thermistor) indicating temperature above 76

°C, the fault line

will be asserted.

When the fan fails continuously, the fault signal will be held on LOW.

su01720

FANXDRIVE

VSENSEx

3.3 V

12 V FAN

+12 V

SI4410DY

RSENSE

(2.2

Ω TYPICAL)

+12 V

3.3 V

Figure 4. Interfacing the 82CF201 to a 2-Wire fan.

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