U2044B_08 Datasheet, PDF (5/9 Pages) ATMEL Corporation – Dual Output Flasher

U2044B
3.6 Lamp Outage Detection (Pin 8)
The lamp current is monitored via an external shunt resistor, R_Shunt and an internal comparator,
K1, with its reference voltage of typically 81 mV (V_S = 12V). The outage of one lamp out of two
lamps is detected according to the following calculation:
Nominal current of 1 lamp: 21W/(V_S = 12V):
Nominal current of 2 lamps: 2 × 21W/(V_S = 12V):
I_lamp = 1.75A
I_lamp = 3.5A
We recommend setting the detection threshold in the middle of the current range: I_outage ≈ 2.7A
Thus the shunt resistor is calculated as:
R_Shunt = V_T (K1)/I_outage
R_Shunt = 81 mV/2.7 A = 30 mΩ
Comparator K1’s reference voltage is matched to the characteristics of filament lamps (see sec-
tion “Control Signal Threshold”).
The combination of the shunt resistor and the resistance of the wire harness prevents pin 8 from
a too high voltage in the case of shorted lamps.
3.7 Supply Voltage (Pin 9)
This pin supplies the oscillator, the comparators and the logic parts of the IC.
3.8 GND (Pin 10)
The integrated circuit is protected against transients according to ISO-TR 7637-3 level 3 via
resistor R₂ to ground (–31). An integrated protection circuit together with external resistors R_2,
R_3, R_4, R_6, R₈ and R₉ limits the current pulses in the IC. The IC is also protected against reversed
battery.
3.9 Control Output Relay 1 and 2 (Pin 11 and 13)
The relay control outputs are high-side drivers with a low saturation voltage and capable of driv-
ing a typical automotive relay with a coil resistance of 60Ω.
3.10 Supply Voltage Power (Pin 12)
This pin supplies the relay drivers connected directly to the battery (Kl 30). It is internally
clamped by a 27-V Z-diode.
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