MC3392 Datasheet, PDF (9/12 Pages) Motorola, Inc – LOW SIDE PROTECTED SWITCH

MC3392
Instrument Panel Lamp Dimmer Control
The MC3392 can be used to control the dimming function
associated with instrument panel lamps. The brightness of
incandescent lamps can be varied by pulse width modulating
the input of the MC3392. The modulating signal for the
MC3392 can be obtained directly from a microprocessor or,
as in Figure 16, from an MC1455 timer. The MC1455 timer is
configured as a free–running clock having both frequency
and duty cycle control. The typical timer frequency is
approximately 80 Hz when the frequency potentiometer is
adjusted to 1.0 k. This frequency was chosen so as to avoid
any perceptible lamp flicker. The duty cycle potentiometer
controls the duty cycle over a range of approximately 3.0% to
97%; When at 3.0% duty cycle, the lamps are essentially off;
When at 97% duty cycle, the lamps are essentially full lit. Six
incandescent lamps are shown in this application drawing
720 mA total current. Similar applications can be used to
drive a variety of lamp loads. The total load current is the
primary factor of consideration when driving lamp loads. The
total value of IO must be less than ISC.
Another convenient aspect of this application is the LED.
The LED can be used to denote the existence of a system
fault (overvoltage, current limiting, or thermal shutdown).
0.01µF
Figure 16. Instrument Panel Lamp Dimmer Control
1
8
2
7
3 ^MC1455 6
4
5
CMOS Input
Vin
+
1.0k
5.0V
–
1N4001
1.0k
Frequency
1N4001
1.0M
Duty Cycle
Fast
Turnoff
Over
Voltage
Detect
Thermal
Shutdown
Current
Limit
Gnd
+
Vout
12V
–
Instrument
Panel Lamps
1.0k
Fault
+
5.0V
–
MOTOROLA ANALOG IC DEVICE DATA
9