6

LT1776

10% and 90% duty cycle. The sync function is internally

disabled if the FB pin voltage is low enough to cause

oscillator slowdown. If unused, this pin should be grounded.

FB (Pin 7): This is the inverting input to the feedback

amplifier. The noninverting input of this amplifier is inter-

nally tied to the 1.24V reference. This pin also slows down

the frequency of the internal oscillator when its voltage is

abnormally low, e.g., 2/3 of normal or less. This feature

helps maintain proper short-circuit protection.

output of the feedback amplifier and the input of the

current comparator. Frequency compensation of the over-

all loop is effected by placing a capacitor, (or in most cases

a series RC combination) between this node and ground.

BLOCK DIAGRA

SWDR

SWDR

SWON

SWON

BOOST

1776 BD

BOOST

SWOFF

SWOFF

LOGIC

OSC

BIAS

FB

GND

SYNC

SHDN

FB

AMP

BOOST

COMP

gm

I

I

I

I

R1

I

COMP

Q4

Q3

Q2

Q1

Q5

D1

5

3

2

1

6

4

8

7