IR2159 datasheet(21/25 Pages) IRF

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IR2159/IR21591 (S)

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detection comparator for 400ns after LO goes 'high'

(Figure 15).

COM

1.6V

RCS

Half

Bridge

Output

LOAD

BUS (+)

BUS (-)

Load

Return

Half

Bridge

Driver

IR2159

PHASE

CONTROL

FAULT

LOGIC

400ns

BLANK

Figure 14, Current sensing circuitry.

The internal blank time reduces the dimming range

slightly (Figure 15) when operating at minimum

phase shift (maximum lamp power). The external

programming resistor on pin MAX must be

selected such that the minimum phase shift is

set a safe margin away from the blank time. A

series resistor (R1) is required to limit the amount

of current flowing out of pin CS when the voltage

across RCS goes below -0.7V. A filter capacitor

at pin CS may be required due to other possible

asynchronous noise sources present in the ballast

system.

BLANK

Switching

Noise

Dimming

Range

Figure 15, Current sense timing diagram.

Fault Mode (FAULT)

During dimming, the peak current regulation circuit

active during preheat and ignition is disabled.

Should non-zero voltage switching at the output

of the half-bridge occur (Figure 18), high current

spikes will result. A lamp filament failure, lamp

end-of-life, lamp removal, or a deadtime shorter

than what is required for commutation, can all

cause hard-switching.

VCS

1.6V

NORMAL

OPERATION

HARD

SWITCHING

FAULT

LOAD

REMOVAL

Figure 18, hard-switching with latch off

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