U643B
Flasher, 30-mW Shunt
Description
The bipolar integrated circuit U643B is used in relay-
controlled automotive flashers where a high-level EMC
is required.
Lamp outage is indicated by frequency doubling during
hazard warning as well as direction mode.
Features
D
Temperature and supply voltage compensated
flashing frequency
D
Frequency doubling indicates lamp outage
D
Relay driver output with high current
carrying capacity and low saturation voltage
D
Minimum lamp load for flasher operation:
≥
1 W
D
Very low susceptibility to EMI
D
Protection according to ISO/TR 7637/1 level 4
Block Diagram
+ V
S
+ 49
6
C
1
4
Measuring comparator K
1
V
6
–81 mV
20 kW
K
1
2
R
3
Shunt
5 kW
7
30 mW
K
2
R
1
Pulse
generator
3
49 a–Comparator K
2
20 kW
49 a–Comparator K
3
K
3
23 V
20 kW
5 kW
IC Ground
1
95 9756
Relay
8
R
2
49 a
1.5...2.2 kW
5
R
4
470
W
5 W 21 W 21 W
21 W 21 W 5 W
Indicator lamps
GND
– 31
Figure 1. Application circuit as a car flasher, Resistor R
1
and R
2
: 1/4 Watt
R
4
for protection against continuous reversed polarity: 0.5 Watt
Ordering Information
Extended Type Number
U643B
U643B-FP
Package
DIP8
SO8
Remarks
Rev. A3, 10-Apr-01
1 (5)
ATMEL [ ATMEL CORPORATION ]
