FAN8903 データシートの表示（PDF） - Fairchild Semiconductor

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FAN8903

Power Window Motor Control IC

Fairchild Semiconductor 

FAN8903(KA3903)

Over Current Protection

Simple Applications

The voltage (Vrs) proportional to the motor current is generated across the resistor (RS). If the Vrs exceeds the reference volt-

age (Vref), over current part-time integration carried out through R3, C2 and OP-amp.

When the amount of over current integration is lager than S2, the over current signal issued.

The cancel time (TC) between motor stall and motor switch-off is determined by following equations;

TC = (C2 × dV) ⁄ IC

where, IC = (Vrs – Vref) ⁄ R3

dV = Vouth – 0.8

You can adjust both the value of the sensing resistor (RS) according to motor type and the cancel time by changing R3 and

C2. Additionally the over current detection of the FAN8903 is immune to any sudden peak current or a current slightly lager

than the reference current.

MOTOR

R3

47k

Vrs

RS

20mΩ

FAN8903

6

C2

474

OP-amp

7

−

+

Vro

−

Vref

0.8V +

OCP

Vro

OCP

S1

S2

Vref

Vrs

Temperature Compensation Applications

Generally speaking, the less ambient temperature, the more motor current. In the previous applications, there are some diffi-

culties to decide the reference current level.

In case of low ambient temperature, the difference between the operating motor current and the reference current is very small.

When the reference current level is high, the margin is large. But at a high ambient temperature, the difference between the

motor current and the stall current is small.

Moreover, the stall current at depends on a battery voltage. It is hard to decide what the optimal reference level is.

In the following figure, in the room temperature, the inverting voltage (V2) and the reference current are calculated as follows;

V2 = Vcom × R3 ⁄ (Rntc + Rt + R3)

Vcom = Vref – V2

The resistance of the NTC decreases according to rising of the ambient temperature. So the reference level, Vcom is changed

with the temperature change as shown in the following figure.

To ensure precision of the reference level, Rt can be adjusted.

8

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