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decrease the output current to the lamp for decreasing the output power. The speed of

the constant power control loop is set by the value of the CPCOMP at the PCOMP pin

that determines how fast the loop will react and adjust the buck on-time over the

changing load conditions.

5.7 Current Limitation Control

The constant power control loop will increase or decrease the buck current for

maintaining constant power in the lamp load. During lamp warm-up, the lamp voltage

can be very low (20V typical) and the constant power loop will attempt to increase the

buck current to several amps of current to maintain constant power. This high current

can exceed the manufacturer’s maximum current rating for the HID lamp. To prevent

this condition, an additional current limitation control loop has been included in the IC

Should the voltage at the ISENSE pin exceed the voltage level at the OC pin, another

OTA will sink current from the ICOMP pin. When the ICOMP pin voltage decreases

below the PCOMP pin voltage, then the current limitation loop will override the constant

power loop and the ICOMP pin will decrease the buck on-time. The lower of the

PCOMP or ICOMP pins will override the other and control the buck on-time. When the

lamp eventually warms up and the lamp voltage increases to a level where the lamp

current is below the maximum allowable limit, then the ICOMP pin voltage will increase

above the PCOMP pin voltage, and the PCOMP pin will control the buck on-time again

for maintaining constant power.

5.8 Buck OFF Mode

The IC will enter the Buck-OFF Mode if any one of these 3 conditions occur:

 VSENSE > VOV or

 PCOMP < 0.2V

or

 ICOMP < 0.2V

When in the Buck-OFF Mode, the IC will go back to General Mode if all of these 3

conditions are valid:

 VSENSE < VOV (2/5)

and

 PCOMP > 0.2V

and

 ICOMP > 0.5V

The IC will instead go back to Ignition Mode if all of these 3 conditions are valid:

 VOV(2/5) < VSENSE < VOV

and

 PCOMP > 0.2V

and