U643B

Rev. A3, 10-Apr-01

2 (5)

Pin Description

Pin

Symbol

Function

1

GND

IC ground

2

3

REL

Relay driver

4

OSC

5

OSC

6

7

LD

Lamp failure detection

8

SI

Start input (49a)

1

2

3

4

8

7

6

5

GND

REL

OSC

SI

LD

Vs

OSC

94 9290

U643B

Figure 2. Pinning

Functional Description

Pin 1, GND

The integrated circuit is protected against damage via

An integrated protection circuit together with external

The arrangement of the supply connections to Pin 2 must

be so as to ensure that, on the connection printed circuit

that to Pin 2.

Pin 3, Relay control output (driver)

The relay control output is a high-side driver with a low

saturation voltage and capable to drive a typical automo-

tive relay with a minimum coil resistance of 60

W.

Pin 4 and 5 Oscillator

nents as follows (see figure 1):

[

1

R

1

C

1

1.5

Hz

where

 47 mF

+ 6.8 kW to 510 kW

In the case of a lamp outage (see Pin 7) the oscillator

[ 2.2

Duty cycle in normal flashing mode: 50%

Duty cycle in lamp outage mode: 40% (bright phase)

Pin 6, Supply voltage, Sense

For accurate monitoring via the shunt resistor, a mini-

recommended.

Pin 7, Lamp outage detection

The lamp current is monitored via an external shunt

of one lamp out of two lamps is detected according to the

following calculation:

The detection threshold is recommended to be set in the

[ 2.7 A

Thus the shunt resistor is calculated as:

W.

Comparator K1‘s reference voltage is matched to the

characteristics of filament lamps (see “control signal

threshold” in the data part).

The combination of shunt resistor and resistance of wire

harness prevents Pin 7 from a too high voltage in the case

of shorted lamps.

Pin 8, Start input

Start condition for flashing: the voltage at Pin 8 has to be

below K3 threshold (flasher switch closed).

Humidity and dirt may decrease the resistance between

49 a and GND. If this leakage resistance is

u 5 kW the IC

is still kept in its off-condition. In this case the voltage at

Pin 8 is between the thresholds of comparators K2 and

K3.

During the bright phase the voltage at Pin 8 is above the

K2 threshold, during the dark phase it is below the K3

threshold. For proper start conditions a minimum lamp

wattage of 1 W is required.