IR2159S datasheet(20/25 Pages) IRF

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0.5V

MIN

DIM

MIN

MAX

USER

SETTING

DIM

RANGE

-90

-180

ΕΕ

REF

Figure 14, Dimming interface

The charging time of CT from 1V to 5.1V

determines the on-time of output gate drivers HO

and LO and corresponds to -180 degrees of

possible phase shift in load current (minus

deadtime). For the 0 to -90 degree dim range, the

voltage on pin MIN is bounded between 1V and

3V using pins MIN and MAX. An external resistor

on pin MAX programs the minimum phase shift

reference (maximum lamp power) corresponding

to 5V on pin DIM, and an external resistor on pin

MIN sets the maximum phase shift (minimum

lamp power) corresponding to 0.5V on pin DIM.

Current Sensing

During dimming, the current sensing circuitry

(Figure 15) detects over-current which can occur

during hard-switching (see Fault section), and

zero-crossing to measure the phase of the total

load current. To reject any switching noise which

can occur at the turn-on of the low-side MOSFET

or IGBT, a digital current sense blanking circuit

blanks out the signal from the zero-crossing

detection comparator for 400ns after LO goes 'high'

(Figure 16).

COM

1.6V

RCS

Half

Bridge

Output

LOAD

BUS(+)

BUS(-)

Load

Return

Half

Bridge

Driver

IR2159

PHASE

CONTROL

FAULT

LOGIC

400ns

BLANK

Figure 15, Current sensing circuitry.

The internal blank time reduces the dimming range

slightly (Figure 16) 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.

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