U6083B_05 Datasheet, PDF (8/13 Pages) ATMEL Corporation – PWM Power Control IC with Interference Suppression

3.7.2
Current Limitation
The lamp current is limited by a control amplifier to protect the external power transistor. The
voltage drop across the external shunt resistor acts as the measured variable. Current limitation
takes place for a voltage drop of V_T1 ≈ 100 mV. Owing to the difference V_T1 – V_T2 ≈ 10 mV, it
ensures that current limitation occurs only when the short-circuit detection circuit has responded.
After a power-on reset, the output is inactive for half an oscillator cycle. During this time, the sup-
ply voltage capacitor can be charged so that current limitation is guaranteed in the event of a
short-circuit when the IC is switched on for the first time.
3.8 Pins 7 and 8, Charge Pump and Output
Pin 8 (output) is suitable for controlling a power MOSFET. During the active integration phase,
the supply current of the operational amplifier is mainly supplied by the capacitor C₃ (bootstrap-
ping). In addition, a trickle charge is generated by an integrated oscillator (f₇ ≈ 400 kHz) and a
voltage doubler circuit. This permits a gate voltage supply at a duty cycle of 100%.
8 U6083B
4770B–AUTO–09/05