ML4836CS datasheet(11/15 Pages) MICRO-LINEAR

11 / 15 page

ML4836

FUNCTIONAL DESCRIPTION (Continued)

After cathode heating, the inverter frequency drops to

FSTART causing a high voltage to appear to ignite the lamp.

If lamp current is not detected when the lamp is supposed

to have ignited, the CX charging current is shut off and the

inverter is inhibited until CX is discharged by RX to the

1.25V threshold. Shutting off the inverter in this manner

prevents the inverter from generating excessive heat when

the lamp fails to strike or is out of socket. Typically this

time is set to be fairly long by choosing a large value of

RX.

LFB OUT is ignored by the oscillator until INTERRUPT is

above 1.20V The CX pin is clamped to about 7.5V.

Care should also be taken not to turn on the VCCZ clamp

so as not to dissipate excessive power in the IC. This will

cause the temp sensor to become active at a lower

ambient temperature.

A summary of the operating frequencies in the various

operating modes is shown below.

OPERATING MODE

OPERATING FREQUENCY

[F(MAX) to F(MIN)]

Preheat

After

Preheat

F(START)

Dimming

Control

F(MIN) to F(MAX)

Figure10. Lamp Starting and Restart Timing

6.75

7.5

4.75

1.25

RX/CX

HEAT

LEA_ENB OR

DIMMING LOCKOUT

INTERRUPT

INHIBIT

ML4836CS Arkusz danych(PDF) 11 Page - Micro Linear Corporation