KA3903 FAIRCHILD [Fairchild Semiconductor], KA3903 Datasheet - Page 8

• Manufacturer Part Number: KA3903
• Description: Power Window Motor Control IC
• Manufacturer: FAIRCHILD [Fairchild Semiconductor]

Over Current Protection
Simple Applications
The voltage (Vrs) proportional to the motor current is generated across the resistor (R
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 (T
You can adjust both the value of the sensing resistor (R
C2. Additionally the over current detection of the FAN8903 is immune to any sudden peak
than the reference current.
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;
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
T
C
V2
Vcom
Vrs
=
MOTOR
=
C2 dV
RS
20m
Vcom
=
R3
47k
Vref V2
C
) between motor stall and motor switch-off is determined by following equations;
–
I
R3
C
C2
474
Rntc
where I
6
7
FAN8903
+
Vref
Rt
,
dV
+
C
OP-amp
R3
+
=
=
Vouth 0.8
Vrs Vref
0.8V
–
–
Vro
S
) according to motor type and the cancel time by
+
R3
OCP
OCP
Vref
Vro
S
S1
). If the Vrs exceeds the reference volt-
current or a current slightly lager
Vrs
S2
changing R3 and
FAN8903(KA3903)