IL6083
Pins 5 and Pin 6, Short-circuit Protection and Current Sensing
Short-circuit Detection and Time Delay, td
The lamp current is monitored by means of an external shunt resistor. If the lamp current exceeds the
threshold for the short-circuit detection circuit (VT2 ≈ 90 mV), the duty cycle is switched over to 100% and the
capacitor C5 is charged by a current source of Ich - Idis. The external FET again is switched off after the cut-
off threshold (VT5) is reached. Switching on the FET again is possible after a power-on reset only. The
current source, Idis, ensures that the capacitor C5 is not charged by parasitic currents.
The time delay, td, is calculated as follows:
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 VT1 ≈ 100 mV. Owing to the difference VT1 - VT2 ≈ 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 supply 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.
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 (bootstrapping). 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%.
Rev. 00
IKSEMICON [ IK SEMICON CO., LTD ]
