U6433B_05 Datasheet, PDF (4/8 Pages) ATMEL Corporation – Flasher, 18-m Shunt, Frequency Doubling Disabling

3. Functional Description
3.1 Pin 1, GND
The integrated circuit is protected against damage via resistor R₄ to ground (–31) in the case of
battery reversal.
An integrated protection circuit together with external resistances R₂ and R₄ limits the current
pulses in the IC.
3.2 Pin 2, Supply Voltage, V_S – Power
The arrangement of the supply connections to pin 2 must be so as to ensure that, on the con-
nection printed circuit board (PCB), the resistance of V_S to pin 6 is lower than that to pin 2.
3.3 Pin 3, Relay Control Output (Driver)
The relay control output is a high-side driver with a low saturation voltage and is capable of driv-
ing a typical automotive relay with a minimum coil resistance of 60Ω.
3.4 Pins 4 and 5, Oscillator
The flashing frequency, f₁, is determined by the R₁C₁ components as follows (see Figure 1-1 on
page 2):
f₁ ≈
-----------------¹-------------------
R₁ × C₁ × 1.5
Hz
where
C₁ ≤ 47 µF
R₁ + 6.8 kΩ to 510 kΩ
In the case of a lamp outage (see pin 7) the oscillator frequency is switched to the lamp outage
frequency f₂ with f₂ ≈ 2.2 × f₁.
Duty cycle in normal flashing mode: 50%
Duty cycle in lamp outage mode: 40% (bright phase)
3.5 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.
3.6 Pin 7, Lamp Outage Detection
3.6.1
Control Signal Threshold 1 (49-mV Comparator K1)
The detection point for lamp failure can be calculated from the control signal threshold, typically
49 mV with V_S = 12V. With a measuring resistance of R₃ = 18 mΩ, the frequency change-over is
reached at a lamp load of 21W + 11.4W. The variation of the control signal threshold supply volt-
age takes into account the PTC characteristic of filament lamps.
4 U6433B
4810B–AUTO–10/05