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(LIGN), capacitor (CIGN), resistor (RIGN2) and switch (MIGN). When the IC turns on the

switch MIGN, capacitor CIGN discharges through resistor RIGN2. When the voltage

across DIGN reaches the diac threshold voltage (Figure 5.4), DIGN turns on and a

current pulse flows from the buck output, through the primary winding of LIGN and into

capacitor CIGN. This arrangement generates a high-voltage pulse on the secondary to

ignite the lamp. The capacitor CIGN charges up until the diac turns off, and CIGN then

discharges down through resistor RIGN until the diac voltage again reaches the device’s

threshold and another ignition pulse occurs.

VL AM P

4K V

VCIG N

VG AT E:M IG N

VD IA C

t

t

VCBU CK

Figure 5.4: Ignition circuit timing diagram

The ignition circuit will continuously try to ignite the HID lamp for 21sec ‘on’ and 64sec

‘off’ until the lamp ignites. If the lamp does not ignite after 1180sec then the IC will enter

Fault Mode and latch off. If the lamp ignites successfully, the voltage at the VSENSE pin

will fall below VOV(2/5) due to the low impedance of the lamp and the ignition timer will

be disabled (logic ‘low’ at the IGN pin).

5.4 General Mode

During General Mode, the IC reacts to the different load conditions (open-circuit, short-

circuit, lamp warm-up, constant power running, under-voltage lamp faults, transient

under-voltage lamp faults, over-voltage lamp faults, lamp non-strike, etc.) by turning the

buck circuit on or off, adjusting the buck circuit on-time, or counting the occurrence of the

different fault conditions and turning the complete IC off. The IC senses the different

load conditions at the VSENSE and ISENSE pins, compares the voltages at these pins

against the programmed thresholds at the OV and OC pins, and determines the correct

operating mode of the IC (see State Diagram).

5.5 Full-Bridge Control

The IC includes a complete high and low-side full-bridge driver necessary for driving the