U643B

Rev. A3, 10-Apr-01

1 (5)

Flasher, 30-m

W 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

20 k

W

5 k

W

20 k

W

5 k

W

23 V

Pulse

generator

IC Ground

20 k

W

1.5...2.2 k

W

Relay

7

3

8

1

+ V

S

+ 49

R

3

470

W

R

4

49 a

4

5

K

2

K

1

K

3

C

1

R

1

6

2

95 9756

49 a–Comparator K

3

49 a–Comparator K

2

21 W 21 W 5 W

21 W

21 W

5 W

GND

– 31

R

2

Indicator lamps

Measuring comparator K

1

Shunt

30 m

W

Ordering Information

Extended Type Number

Package

Remarks

U643B

DIP8

U643B-FP

SO8