Features
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Interval Pause: 4s to 20s
After-wiping Time: 2s to 20s
Wiper Motor’s Park Switch
Wipe/Wash Mode Priority
One External Capacitor Determines All Time Sequences
Relay Driver with Z-diode
Interference Protection According to VDE 0839 or ISO/TR 7637/1
Load-dump Protected
1. Description
The U642B is a bi-polar integrated circuit designed for the wiper application in the
automotive market. It includes wipe, wash and internal mode.
2. Functional Description
As a convenience feature of the windshield wiper, intermittent and wipe/wash opera-
tion functions are implemented in most of the automobiles. The U642B is a
cost-effective solution for an accurate timing function control. Wipe/wash mode has
priority over interval mode. Interval pause and after-wiping time can be set to fixed val-
ues by using resistors in a broad time range. Added value can be provided with an
individual, continuous adjustment of the interval pause by a potentiometer which may
be built into the stalk. For proper operation, it is mandatory to feed the signal of the
wiper motor's park switch into U642B.
Interval and
Wipe/Wash
Wiper Control
IC
U642B
4774C–AUTO–10/07
4. Circuit Description
4.1
Interval Function, Pin 2
By closing the interval switch, S
2
, to supply voltage, V
Batt
, the relay is activated. The internal cur-
rent source (pin 3) which holds the capacitor C
2
in a charged state is switched-off. As soon as
there is a positive potential at the park switch (S
1
), the current source F (see
Figure 2-1 on page
2)
charges the capacitor C
2
very quickly. After the wiper operation is finished, S
1
is again at
ground potential, the relay is in the off position - interval pause begins - the capacitor C
2
is dis-
charged through the current source C, till the voltage at pin 3 is below the threshold of 2V.
Interval pause can be adjusted between 4s to 20s with the help of potentiometer R
3
. Now the
relay switches on and the next interval cycle begins. Opening of switch S
2
causes the current
source A to discharge C
2
immediately and current sources C and F are switched-off.
4.2
Wipe/Wash (WIWA) Operation, Pin 5
By closing the WIWA switch, S
3
, to supply voltage, V
Batt
, the water pump starts spraying water
on the windshield. During this function, the current source A is switched-off which keeps the
capacitor C
2
in a discharged state. Now the capacitor is charged through the current sources D
and F. If (after a time interval of approximately 100 ms) the voltage at the capacitor is greater
than 6.5V, the relay is turned on as long as the switch WIWA is closed.
The after-wiping time begins when the switch is open, the sources D and F are switched off and
the source E is activated. Source E discharges the capacitor until the voltage is less than 2.2V.
The relay is off and the wiper-motor is supplied via the park switch until the park position is
reached. The after-wiping time is determined by the current source E which can be regulated
with the external resistor R
Time
. When the after-wiping time has elapsed, the source A dis-
charges the capacitor. The relay switch is independent of the park switch S
1
.
4.3
Interval and WIWA Functions
The interval function is interrupted immediately when the wipe/wash mode is activated. The cur-
rent source A discharges the capacitor to a value of 2V, afterwards, the normal wash function
starts.
Interval wiping starts immediately when the after-wipe time is over. The switching delays are
slightly shorter, because the capacitor is already charged to a value of 2V.
The wipe/wash function is not interrupted when the interval switch S
2
is activated. The interval
function begins after the WIWA function has elapsed.
4
U642B
4774C–AUTO–10/07
Embedded System
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