U6043B_05 Datasheet, PDF (4/8 Pages) ATMEL Corporation – Flasher IC with 18-mOHM Shunt

4.4 Pin 4 and 5, Oscillator
The flashing frequency, f₁, is determined by the R₁C₁ components as given by the following for-
mula below (see Figure 2-1):
1^≈
-----------------¹-------------------
R₁ × C₁ × 1,5
Hz
where C₁ ≤47 µF, R₁ = 6.8 kΩ to 510 kΩ
In case of a lamp outage (see Pin 7) the oscillator frequency is switched to the lamp outage fre-
quency f₂ with f₂ ≈ 2.2 × f₁.
Duty cycle in normal flashing mode: 50%
Duty cycle in lamp outage mode: 40% (bright phase)
4.5 Pin 6, Supply Voltage, Sense
For accurate monitoring via the shunt resistor, a minimized layer resistance from point V_S/shunt
to Pin 6 is recommended.
4.6 Pin 7, Lamp Outage Detection
The lamp current is monitored via an external shunt resistor R_sh and an internal comparator K1
with its reference voltage of typically 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 mΩ
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.
4.7 Pin 8, Start Input
Start condition for flashing: the voltage at Pin 8 has to be below the K3 threshold (flasher switch
closed).
Humidity and dirt may decrease the resistance between 49 a and GND. If this leakage resis-
tance is > 5 kΩ, the IC is still kept in the 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.
4 U6043B
4726B–AUTO–11/05