IR2159S datasheet(17/25 Pages) IRF

17 / 25 page

IR21592/IR21593(S)

www.irf.com

60uA

-1uA

CVCO

RCS

IPH

Figure 8, Peak load current regulation timing diagram.

This feedback keeps the peak preheat current

regulated to the user-programmable setting on pin

IPH for the duration of the preheat time. An

internal current source connected to an external

resistor on pin IPH sets a voltage reference for

the peak pre-heat current. The pre-heat time

continues until the voltage on pin CPH exceeds

5V.

Ignition (IGN)

The IR21592/IR21593 enters ignition mode when

the voltage on pin CPH exceeds 5V. The peak

current regulation reference voltage is

disconnected from the user-programmable

setting on pin IPH and is connected to a higher

internal threshold of 1.6V (Figure 9).

7.6V

1uA

CPH

DIM

VCO

COM

1uA

1.6V

RCS

VCO

LOGIC

DIM

CPH

VCO

Half

Bridge

Output

LOAD

BUS(+)

BUS(-)

Load

Return

Half

Bridge

Driver

IR21592/IR21593

DIM

INTERFACE

0.5 to 5V

PHASE

CONTROL

FAULT

LOGIC

Figure 9, IR21592/IR21593 ignition circuitry.

The ignition ramp is then initiated as the

capacitor on pin VCO discharges linearly

through an internal 1uA current source. The

frequency decreases linearly towards the

resonance frequency of the high-Q ballast output

stage, causing the lamp voltage and load current

to increase (Figure 10).

The frequency

continues to decrease until the lamp ignites or

the current limit of the IR21592/IR21593 is

reached. If the current limit is reached, the

IR21592/IR21593 enters FAULT mode. The 1.6V

threshold together with the external current

sensing resistor on pin CS determine the

maximum allowable peak ignition current (and

therefore peak ignition voltage) of the ballast

output stage. The peak ignition current must not

exceed the maximum allowable current ratings

of the output stage MOSFETs or IGBTs, and,

the resonant inductor must not saturate at

any time.

To prevent a "flash" across the lamp during

ignition at low dim settings, an ignition detection

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