Microsemi

Linfinity Microelectronics Division

11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570

Page 1

Copyright

© 2000

Rev. 1.1b,2005-03-09

LX1681/1682

Voltage-Mode PWM Controllers

TM

®

DESCRI PTI O N

The LX1681/1682 are monolithic,

pulse-width modulator controller ICs.

They are designed to implement a

flexible, low cost buck (step-down)

regulator supply with minimal external

components.

The LX1681 is a non-synchronous

controller;

the

LX1682

has

a

synchronous driver for higher efficiency.

The output voltage is adjustable by

means of a resistor divider to set the

voltage between 1.25V and 4.5V.

Short-circuit current limiting can be

implemented without expensive current

sense resistors. Current is sensed using

MOSFET — sensing is delayed for 1µs

to eliminate MOSFET ringing errors.

Hiccup-mode fault protection reduces

average power to the power elements

during short-circuit conditions.

Switching frequency is fixed at

200kHz for optimal cost and space.

Under-voltage lockout and soft-start

for optimal start-up performance. Pulling

the soft-start pin to ground can disable

the LX1681/82.

Small 8-pin SOIC packaging reduces

board space. Optimized for 5V-to-3.3V

or

5V-to-2.5V

conversion,

the

LX1681/82 can also be used for

converting 12V to 5V, 3.3V or other

voltages

with

high

efficiency,

eliminating the need for bulky heat sinks.

IMPORTANT:

For the most current data, consult MICROSEMI’s website: http://www.microsemi.com

KEY FEATUR ES

Fixed 200kHz Switching Frequency

Constant Frequency Voltage-Mode

Control Requires NO External

Compensation

Hiccup-Mode Over-Current

Protection

High Efficiency

Output Voltage Set By Resistor

Divider

Under-Voltage Lockout

Soft-Start And Enable

Synchronous Rectification

(LX1682)

Non-Synchronous Rectification

(LX1681)

Small, 8-pin Surface Mount

Package

APPLI CATI ONS

5V to 3.3V Or Less Buck

Regulators

FPGA Supplies

Microprocessor Chipset Supplies

(e.g. Camino, Whitney, etc.)

Rambus

Hard Disk Drives

Computer Add-on Cards

PRODUCT H I GHLIGHT

LX1681

0.1µF

Q

1

D

2

L

1

C

2

R

1

R

2

R

SET

C

1

C

3

V

FB

C

SS

N.C.

GND

TDRV

V

C1

CS

V

C2

V

BO O ST

12V

V

IN

5V

V

OU T

SS

LX1681 Non-Synchronous Controller

5µH

1500µF

x3

IRL3103S

MBR 2545

1500µF

x3

1µF

LX1682

0.1µF

Q

1

L

1

C

2

R

1

R

2

R

SET

C

1

V

FB

C

SS

BDR V

GND

TD RV

V

C1

CS

V

C2

V

IN

5V

V

OU T

SS

Q

2

C

3

V

BO O ST

12V

LX1682 Synchronous C ontroller

1500µF

x3

5µH

IR L3103S

IRL3103S

1500µF

x3

1µF

PACKAGE ORDER I N FO

DM

Plastic SOIC

8-PIN

°C)

RoHS Compliant / Pb-free

Transition D/C: 0440

0 to 70

Non-Synchronous

LX1681CDM

Synchronous

LX1682CDM

Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. LX1681CDM-TR)