ML4836CS datasheet(8/15 Pages) MICRO-LINEAR

8 / 15 page

ML4836

FUNCTIONAL DESCRIPTION (Continued)

INTERRUPT

RX/CX

3.8/1.2V

–

1.20/1.0V

0.625

RSET

VCC

RT2

REF

LEA_ENB

RT2

–

RT/CT

7.5mA

ICHG

DURING PREHEAT

AFTER PREHEAT

LEA_ENB = HI

LEA_ENB = LOW

RSET

CHG =

2.5V

RSET

CHG =

8K±25%

–

7.5V

RSET

CHG =

8K±25%

– LEAO

NOTE 1: RSET SHOULD BE SELECTED SUCH THAT AFTER PREHEAT WITH LEA_ENB "HI",

ICHG MUST BE < 0.

ICHG IS A UNI-DIRECTIONAL SOURCE CURRENT ONLY.

4.65/1.75V

–

7.5V

CLOCK

VTH = 3.8V

VTL = 1.2V

tDIS

tCHG

EOL and the ML4836

The ML4836 uses a circuit that creates a DC voltage

representative of the power supplied to the lamps through

the inverter when use in conjuction with PFC. This voltage

is used by the ML4836 to latch off the ballast when it

exceeds an internal threshold. An external resistor can be

used as the “EOL latch resistor” to set the power level trip

point, as shown in by R9 in Figure 6.

BALLAST OUTPUT SECTION

The IC controls output power to the lamps via frequency

modulation with non-overlapping conduction. This means

that both ballast output drivers will be low during the

discharging time tDIS of the oscillator capacitor CT.

OSCILLATOR

The VCO frequency ranges are controlled by the output

of the LFB amplifier (RSET). As lamp current decreases,

LFB OUT falls in voltage, causing the CT charging current

to increase, thereby causing the oscillator frequency to

increase. Since the ballast output network attenuates high

frequencies, the power to the lamp will be decreased. The

oscillator frequency is determined by the following

equations:

Figure 7. Oscillator Block Diagram and Timing

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