Features
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Interval Pause: 4 to 20 s
After-wiping Time: 2 to 20 s
Wiper Motor's Park Switch
0.6 s Prewash Delay
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
Description
The U641B is a bi-polar integrated circuit designed for the wiper application in the
automotive market. It includes wipe, wash and internal mode.
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 U641B 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 values 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 the U641B.
Figure 1.
Block Diagram
V
S
8
OUT
7
PARK
6
V
Ref
Park switch
comparator
WASH
5
V
Ref
Input
comparator
Interval and
Wipe/Wash
Wiper Control
IC with Delay
U641B
Load-dump
comparator
V
Ref
Logic
V
Ref
Wipe/wash
comparator
Interval
comparator
A
B
C
D
E
F
1
GND
2
INT
3
C
t
4
R
t
Rev. 4773A–AUTO–11/03
U641B
Circuit Description
Interval Function, Pin 2
By closing the interval switch, S
2
, to supply voltage, V
Batt
, the relay is activated. The
internal current source (pin 3) which holds the capacitor C
2
in charged state is switched-
off. As soon as there is a positive potential at the park switch (S
1
), current source F
(see Figure 1 on page 1) charges the capacitor C
2
very quickly. After the wiper opera-
tion is finished, S
1
is again at ground potential, the relay is in the off position - interval
pause begins - the capacitor C
2
is discharged through the current source C, till the volt-
age at pin 3 is below the threshold of 2 V. Interval pause can be adjusted between 4 s to
20 s with the help of potentiometer R
3
. Now the relay switches on and the next interval
cycle begins. Opening switch S
2
causes current source A to discharge C
2
immediately
and current sources C and F are switched off.
By closing the WIWA switch, S
3
, to supply voltage, V
Batt
, the water pump starts spraying
the 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 source F. If (after a time interval of approximately 600 ms) the volt-
age at the capacitor is greater than 6.1 V, 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 2.2 V. 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 discharges the capacitor. The relay switch is independent of the
park switch S
1
.
Wipe/Wash (WIWA)
Operation, Pin 5
Interval and WIWA
Functions
The interval function is interrupted immediately when the switch S
2
is activated. The cur-
rent source A discharges the capacitor to a value of 2 V, 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 2 V.
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.
3
4773A–AUTO–11/03
U641B
Absolute Maximum Ratings
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress rating
only and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of this
specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
Parameters
Supply voltage t = 60 s, terminal 15
Supply current
t = 2 ms
t = 200 ms
Relay control output current (DC)
t = 200 ms
Park switch, S
1
Wipe/Wash switch, S
3
Interval switch, S
2
Power dissipation T
amb
= 90°C
Storage temperature range
Ambient temperature range
Pin
8
8
Symbol
V
Batt
I
8
I
8
I
7
I
7
I
6
I
5
I
2
P
tot
T
stg
T
amb
Value
28
1.5
150
200
1.2
50
50
50
500
-55 to +125
-40 to +85
Unit
V
A
mA
mA
A
7
Pulse Current (Control Inputs) t = 200 ms
6
5
2
mA
mW
°C
°C
Thermal Resistance
Parameters
Junction ambient
DIP8
SO8
Symbol
R
thJA
R
thJA
Value
120
160
Unit
K/W
K/W
5
4773A–AUTO–11/03
Microchip MCU
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