DESCRIPTION

KEY FEA TURES

s Fixed 200kHz Switching Frequency

s Constant Frequency Voltage-Mode Control

Requires NO External Compensation

s Hiccup-Mode Over-Current Protection

s High Efficiency

s Output Voltage Set By Resistor Divider

s Under-Voltage Lockout

s Soft-Start And Enable

s Synchronous Rectification (LX1682)

s Non-Synchronous Rectification (LX1681)

s Small, 8-pin Surface Mount Package

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 mini-

mal external components.

The LX1681 is a non-synchronous con-

troller; 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 the

voltage drop across the R

— 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.

The

LX1681/82 can be disabled by pulling the soft-

start pin to ground.

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.

PRODUCT HIGHLIGHT

OF

APPLICA TIONS

s 5V to 3.3V Or Less Buck Regulators

s FPGA Supplies

s Microprocessor Chipset Supplies

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

s Hard Disk Drives

s Computer Add-on Cards

Note: All surface-mount packages are available in Tape & Reel,

append the letter "T" to part number. (i.e. LX1681CDMT)

PACKAGE ORDER INFORMA TION

T

0 to 70

Non-Synchronous

LX1681CDM

Synchronous

LX1682CDM

Copyright © 1999

Rev. 1.0 5/99

1

Plastic SOIC

8-pin

DM

LX1681/1682

Output

LX1681

V

BOOST

12V

8

7

6

5

4

3

2

1

V

FB

SS

N.C.

GND

V

CC

CS

V

C1

TDRV

V

IN

5V

C

SS

V

OUT

R

SET

R

1

R

2

C

3

1µF

C

1

1500µFx3

Q

1

IRL3103S

D

2

MBR2545

L

1

5µH

C

2

0.1µF

1500µF

x3

LX1682

V

BOOST

12V

8

7

6

5

4

3

2

1

V

FB

SS

GND

BDRV

V

CC

CS

V

C1

TDRV

V

IN

5V

C

SS

V

OUT

R

SET

R

1

R

2

C

2

L

1

5µH

Q

1

IRL3103S

Q

2

IRL3103S

C

1

1500µFx2

C

3

1µF

0.1µF

1500µF

x3

NOTE: For current data & package dimensions, visit our web site: http://www.linfinity.com.