U842B
Block Diagram
VS
GND
7
6
Stabilization
POR
Load–dump –
detection
21 V
8
1/2 VS
OUT
28 V
+
1
–
INT
250 mV
+
–
25 pF 21 V
0.5 Ω
+
–
Logic
2
WASH
PARK
25 pF 21 V
3
+
–
Oscillator
VS
OUT
25 pF 21 V
+
–
Upper
switching
point
21 V
25 pF 21 V
PAUS
4
5
13287
OSC
Figure 2. Block diagram
Basic Circuit
Power Supply
Oscillator
All timing sequences in the circuit are derived from an RC
oscillator which is charged by an external resistor, R and
For reasons of interference protection and surge immu-
nity, a RC circuitry has to be provided to limit the current,
and to supply the integrated circuit in the case of supply
voltage drops.
9,
discharged by an integrated 2-k
resistor. The basic
frequency, f is determined by the capacitor, C and an
0,
2,
integrated voltage divider. The basic frequency is
adjusted to 320 Hz (3.125 ms) by C = 100 nF and
2
Suggested values: R = 180
C = 47 F,
1
1
R = 220 k .
9
(see figure 2)
The tolerances and the temperature coefficients of the ex-
ternal components determine the precision of the
oscillator frequency. A 1% metallic-film resistor and a
5% capacitor are recommended..
The supply (Pin 6) is clamped with a 21-V Zener diode.
The operation voltage ranges between V = 9 V to 16 V.
Batt
The capacitor, C can be dimensioned smaller (typically: The debouncing times of the inputs, the turn-on time of
1,
10 F) if a diode is used in the supply against polarity re- the relay (t ), the pre-wash delay (t ), the dry wiping time
5
1
versal. In this case of negative interference pulses, there, (t ) and the debouncing time (t , short circuit detection)
2
7
is only a small discharge current of the circuit.
depend on the oscillator frequency (f ) as follows:
0
2 (12)
TELEFUNKEN Semiconductors
Rev. A2, 03-Feb-97
TEMIC [ TEMIC SEMICONDUCTORS ]
