Functional Description
Pin 1, GND
The U6043B is protected against damage in case of battery reversal via resistor R
4
to
ground (-31). An integrated protection circuit together with external resistances R
2
and
R
4
limits the current pulses in the IC.
The arrangement of the supply connections to Pin 2 (and 6) must be so as to ensure
that on the connection printed circuit board (PCB), the resistance of V
S
to Pin 6 is lower
than that to Pin 2.
The relay control output is a high-side driver with a low saturation voltage. It is capable
of driving a typical automotive relay with a minimum coil resistance of 60
W
.
The flashing frequency, f
1
, is determined by the R
1
C
1
components as given by the fol-
lowing formula below (see Figure 1):
1
-
f
1
»
----------------------------------
Hz
R
1
´
C
1
´
1.5
Pin 2, Supply Voltage,
V
S
power
Pin 3, Relay Control
Output (Driver)
Pin 4 and 5, Oscillator
where C
1
£
47 µF, R
1
= 6.8 k
W
to 510 k
W
In case of a lamp outage (see Pin 7) the oscillator frequency is switched to the lamp out-
age frequency f
2
with f
2
»
2.2
´
f
1
.
Duty cycle in normal flashing mode: 50%
Duty cycle in lamp outage mode: 40% (bright phase)
Pin 6, Supply Voltage,
Sense
Pin 7, Lamp Outage
Detection
For accurate monitoring via the shunt resistor, a minimized layer resistance from point
V
S
/shunt to Pin 6 is recommended.
The lamp current is monitored via an external shunt resistor R
sh
and an internal compar-
ator K1 with its reference voltage of typ. 49 mV (V
S
= 12 V). The outage of one lamp is
detected according to the following calculation:
Nominal current of 1 lamp: 21 W/(V
S
= 12 V): I
lamp
= 1.75 A
Nominal current of 2 lamps: 2
´
21 W/(V
S
= 12 V): I
lamp
= 3.5 A
We recommend setting the detection threshold in the middle of the current range:
I
outage
»
2.7 A
Thus, the shunt resistor is calculated as:
R
sh
= V
T
(K1)/I
outage
R
sh
= 49 mV/2.7 A = 18 m
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 case of shorted lamps.
4
U6043B
4726A–AUTO–06/03
ATMEL [ ATMEL CORPORATION ]
