LX1745

Microsemi

Integrated Products Division

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

Page 1

Triple Output Boost – LED Driver / LCD Bias

Copyright

© 2000

Rev. 1.2, 2006-02-27

TM

®

DESCRIPTION

The LX1745 is a compact high

efficiency step-up boost regulator for

driving white or color LEDs in LCD

lighting applications while supplying the

necessary LCD bias voltages with an

additional two integrated boost converters.

Designed for maximum efficiency and

featuring

a

psuedo-hysteretic

PFM

topology (that decreases output voltage

ripple), the LX1745 minimizes system cost

and condenses layout area making it ideal

for PDA, smart-phone, and digital camera

applications.

While the LCD Bias generation is

implemented using an internal N-Channel

MOSFET for LCD Bias generation, the

LED driver utilizes an external N-Channel

MOSFET in order to maintain maximum

efficiency along with flexible power

requirements..

The LX1745’s control circuitry is

optimized for portable systems with a

shutdown current of less than 1µA. The

input voltage range of 1.6V to 6.0 allows

for a wide selection of system battery

voltages

and

start-up

is

sustained operation as low as 1.1V.

The maximum LED drive current is

easily programmed using one external

current sense resistor in series with the

LEDs. In this configuration, LED current

provides a feedback signal to the FB pin,

maintaining constant current regardless of

varying

LED

forward

voltage

Depending on the MOSFET selected, the

LX1745 is capable of achieving an LED

drive in excess of 1.0W.

The LX1745 provides simple dynamic

adjustment of the LED drive current (0% to

100% full range dimming) and the LCD

Bias output voltages (up to

±15% typ)

through separate IC interfaces.

Each

interface has an internal RC filter allowing

designers to make these adjustments via a

direct PWM input signal or an analog

reference signal.

Further, any PWM

amplitude is easily accommodated using a

single external resistor.

The LX1745 is available in the low-

profile 20-Pin TSSOP.

IMPORTANT:

KEY FEATUR ES

> 90% Maximum Efficiency

Low Quiescent Supply Current

Externally Programmable Peak

Inductor Current Limit For

Maximum Efficiency

Logic Controlled Shutdown

< 1µA Shutdown Current

Dynamic Output LED Current

and Two LCD Bias Voltage

Adjustments Via Analog

Reference Or Direct PWM

Input

20-Pin TSSOP Package

APPLI C ATION S

Pagers

Smart Phones

PDAs

Handheld Computers

General LCD Bias Applications

LED Driver

PRODUCT H I GHLIGHT

C

1

4.7μF

L

1

47

μH

1206 Case Size

LX1745

LFB

CS

DRV

IN

SRC

R

SET

15Ω

V

I

OVP

SW1

V

FB1

- V

LCD

BRT

LSHDN

ON OFF

SW2

FB2

V

REF

ADJ1

SHDN1

ON OFF

GND

ADJ2

SHDN2

ON OFF

LX1745 Evaluation Board

PACKAGE ORDER INFO

PW

Plastic TSSOP

20-Pin

RoHS Compliant / Pb-free

Transition DC: 0442

-40 to 85

LX1745CPW

Note: Available in Tape & Reel. Append the letters “TR”

to the part number. (i.e. LX1745CPW-TR)