IR2157 データシートの表示（PDF） - International Rectifier

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IR2157

FULLY INTEGRATED BALLAST CONTROL IC

International Rectifier 

IR2157

ADVANCED INFORMATION

Recovery from such a fault condition is accomplished

by cycling either SD pin or the VCC pin. When a

lamp is removed, the SD pin goes high, the fault

latch is reset, and the chip is held off in an unlatched

state. Lamp replacement causes the SD pin to go

low again, reinitiating the startup sequence. The

fault latch can also be reset by the undervoltage

lockout signal, if VCC falls below the lower

undervoltage threshold.

Bootstrap Supply Considerations

Power is normally supplied to the high-side circuitry

by means of a simple charge pump from VCC, as

shown in Figure 19 below.

Figure 17: Operation below resonance

Figure 18: Auto restart for lamp replacement

VDC

1

CPH

2

RPH

3

RT

4

RUN

5

CT

6

DT

7

SD

8

rectified

AC line

+V BUS

HO

16

Q1

VS

15

RGHS

VB

14

N/C

13

VCC

12

CBOOT

R SUPPLY

DBOOT

D1

COM

11

CVCC

LO

10

CS

9

Q2

RGLS

R3

RCS

1/2 Bridge output

RSNUBBER

CSNUBBER

D2

VBUS return

Figure 19: Typical bootstrap supply connection

with VCC charge pump from half-bridge output

(shaded area)

A high voltage, fast recovery diode DBOOT (the so-

called bootstrap diode) is connected between VCC

(anode) and VB (cathode), and a capacitor CBOOT

(the so-called bootstrap capacitor) is connected

between the VB and VS pins. During half-bridge

switching, when MOSFET Q2 is on and Q1 is off, the

bootstrap capacitor CBOOT is charged from the VCC

decoupling capacitor, through the bootstrap diode

DBOOT, and through Q2. Alternately, when Q2 is off

and Q1 is on, the bootstrap diode is reverse-biased,

16

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