Copyright © 1994

Rev. 1.0a

1/01

FOR FU R THER INFORM A TION CALL (714) 898-8121

1

OF

LX1552/3/4/5

DESCRIPTION

KEY FE A TURES

s

s

s

s

s ULTRA-LOW START-UP CURRENT

(150µA typ.)

s

s

s

s

s TRIMMED OSCILLATOR DISCHARGE

CURRENT

(±2% typ.)

s

s

s

s

s INITIAL OSCILLATOR FREQUENCY BETTER

THAN ±4%

s

s

s

s

s OUTPUT PULLDOWN DURING UVLO

s

s

s

s

s PRECISION 2.5V REFERENCE (±2% max.)

p CURRENT SENSE DELAY TO OUTPUT

(150ns typ.)

p AUTOMATIC FEED FORWARD

COMPENSATION

p PULSE-BY-PULSE CURRENT LIMITING

p ENHANCED LOAD RESPONSE

CHARACTERISTICS

p UNDER-VOLTAGE LOCKOUT WITH

HYSTERESIS

p DOUBLE PULSE SUPPRESSION

p HIGH CURRENT TOTEM POLE OUTPUT

(±1Amp peak)

p 500kHz OPERATION

The LX155X family of ultra-low start-up

current (250µA max.), current mode

control IC's offer new levels of energy

efficiency for offline converter applica-

tions. They are ideally optimized for

personal computer and CRT power

supplies although they can be used in

any number of off-line applications

where energy efficiency is critical.

Coupled with the fact that the LX155X

series requires a minimal set of external

components, the series offers an

excellent value for cost conscious

consumer applications.

Optimizing energy efficiency, the

LX155X series demonstrates a signifi-

cant power reduction as compared with

other similar off-line controllers. Table 1

compares the SG384X, UC384XA and

the LX155X start-up resistor power

dissipation. The LX155X offers an

overall 4X reduction in power dissipa-

tion. Additionally, the precise oscillator

discharge current gives the power

supply designer considerable flexibility

in optimizing system duty cycle

consistency.

The current mode architecture

demonstrates improved load regulation,

pulse by pulse current limiting and

inherent protection of the power supply

output switch. The LX155X includes a

bandgap reference trimmed to 1%, an

error amplifier, a current sense com-

parator internally clamped to 1V, a high

current totem pole output stage for fast

switching of power mosfet's, and an

externally programmable oscillator to

set operating frequency and maximum

duty cycle. The undervoltage lock-out

circuitry is designed to operate with as

little as 250µA of supply current

permitting very efficient bootstrap

designs.

PRODUCT HIGHLIGHT

P ACKAGE ORDER INFORM A TION

T

Plastic DIP

8-pin

0 to 70

LX155xCM

LX155xCDM

LX155xCD

—

LX155xCPW

-40 to 85

LX155xIM

LX155xIDM

LX155xID

—

—

-55 to 125

—

—

—

LX155xMY

—

M

Plastic SOIC

8-pin

DM

Plastic SOIC

14-pin

D

Ceramic DIP

8-pin

Y

TSSOP

20-pin

PW

Max. Start-up Current

Specification (I

Typical Start-Up

Resistor Value (R

Max. Start-Up Resistor

Power Dissipation (P

Design Using

SG384x UC384xA LX155x

62K

Ω

Ω

Ω

Ω

Ω 124KΩ

Ω

Ω

Ω

Ω

Ω

Ω

Ω

Note: Calculation is done for universal AC input speci-

fication of V

following equation: (Resistor curr ent is selected to be

2 * I

R

, P

V

AC MIN

√2 * I

ST

2V

AC

2

MAX

R

ST

APPLIC A TIONS

s

s

s

s

s ECONOMY OFF-LINE FLYBACK OR

FORWARD CONVERTERS

s DC-DC BUCK OR BOOST CONVERTERS

s LOW COST DC MOTOR CONTROL

Part #

Start-Up Hysteresis Max. Duty

Voltage

Cycle

LX1552

16V

6V

<100%

LX1553

8.4V

0.8V

<100%

LX1554

16V

6V

<50%

LX1555

8.4V

0.8V

<50%

V

CC

AC

INPUT

LX1552

or

LX1554

Note: All surface-mount packages are available in Tape & Reel. Append the letter "T" to part number. (i.e. LX1552CDMT)