3

FN7428.9

July 13, 2006

Block Diagram

Pin Descriptions

PIN NUMBER

PIN NAME

PIN FUNCTION

1

SGND

Negative supply for the controller stage

2

PGND

Negative supply for the power stage

3

LX

Inductor drive pin; high current digital output with average voltage equal to the regulator output voltage

4

VIN

Positive supply for the power stage

5

VDD

Power supply for the controller stage

6

SYNC

SYNC input pin; when connected to HI, regulator runs at forced PWM mode; when connected to Low, auto

PFM/PWM mode; when connected to external sync signal, at external PWM frequency up to 12MHz

7

EN

Enable

8

PG

Power-Good open drain output

9

VO

Output voltage sense

10

FB

output

-

+

-

+

-

+

-

+

-

+

CONTROL

LOGIC

PFM

ON-TIME

CONTROL

PWM

COMPENSATION

RAMP

GENERATOR

UNDER-

VOLTAGE

LOCKOUT

POWER

GOOD

CLOCK

SOFT-

START

BANDGAP

REFERENCE

TEMPERATURE

SENSE

+

–

LX

PGND

PG

FB

SYNC

EN

SGND

10pF

5M

124K

100K

10µF

3.3V

SYNC

EN

PWM

COMPARATOR

PWM

COMPARATOR

SYNCHRONOUS

RECTIFIER

N-DRIVER

P-DRIVER

CURRENT

SENSE

INDUCTOR SHORT

1.8µH

10µF

100K

PG

1.8V

0 TO 1A

100

Ω

0.1µF

C4

470pF

EL7531