1996 Sep 04 5
Philips Semiconductors Product specification
Light position controller TDA3629
FUNCTIONAL DESCRIPTION
The device is intended to control the elevation of the light
beam of a head light of a passenger car. The driver can
control the elevation of the light beam by rotating a
potentiometer on the dashboard (the setting
potentiometer). The device adapts the elevation of the light
beam by activating the control motor. The elevation of the
head light is fed back to the device by a second
potentiometer (the feedback potentiometer).
This feedback potentiometer is mechanically coupled to
the motor.
The device operates only when the supply voltage is within
certain limits. The device is switched off outside these
boundaries. The under voltage detection detects whether
the supply voltage is below the under voltage threshold.
The motor will not be activated when this occurs, but it
remains short-circuited by the output stages.
The over voltage will switch off the total device when the
supply voltage is higher than the over voltage threshold.
A thermal protection circuit becomes active if the junction
temperature exceeds a value of approximately 160 °C.
This circuit will reduce the motor current, which will result
in a lower dissipation and hence a lower chip temperature.
This condition will only occur when the motor is blocked at
high ambient temperature.
A detection of a broken wire of the slider of the setting
potentiometer is included because it will be connected to
the device by a wire several meters long. This detection
circuit prevents the motor from rotating when the wire is
broken. In this event the brake will remain active.
The protection of V
SET
to V
P
circuit prevents the motor
from rotating when the voltage at the V
SET
input is above
the threshold value. This can be used to detect whether
the wire from the slider of the setting potentiometer is
short-circuited to the battery line. A protection of V
SET
short-circuited to ground is also present. The motor will be
stopped if V
SET
becomes lower than the threshold level.
The shaded areas in Fig.4 represent the parts where the
short-circuit protection stages are active. Figure 4 shows
that a position of 0 mm can not be reached, neither can a
position of 100%. The minimum position that can be
reached depends on the battery voltage V
b
, although the
maximum position does not.
The device is protected against electrical transients which
may occur in an automotive environment. The device will
shut off when positive transients on the battery line occur
(see Figs 7 and 8). The motor will not be short-circuited in
this event. The flyback diodes, illustrated in Fig.1, will
remain present. The state of the output stages at the
moment when the transient starts is preserved by internal
flip-flops. Negative transients on the battery line
(see Figs 7 and 8) will result in a set short-circuited to
ground fault detection, because it will result in a voltage at
the setting input which is below the short-circuited to
ground threshold. The device however discharges the
electrolytic capacitor during these transients. It will stop
functioning when the resulting supply voltage becomes too
low.
Fig.4 Conversion gain.
handbook, halfpage
MGE635
100
position
(%)
0
0
V
SET(min)
V
SET(max)
V
SET
(V)
V
b
