JULY 2000

LCD Backlight Lamp Driver with Contrast

1

GENERAL DESCRIPTION

The ML4876 is an ideal solution for driving small cold

cathode fluorescent tubes (CCFL) used in liquid crystal

display (LCD) backlight applications. It provides the

dimming ballast control and the contrast control for the

LCD display.

By utilizing differential drive the ML4876 can deliver the

same light output with significantly less input power

compared to existing single ended drive schemes.

Improvements as high as 30% can be realized when using

low power lamps and advanced LCD screen housings. This

increased light output is achieved because the differential

drive configuration is much less sensitive, and therefore

less power is wasted in the capacitive parasitics that exist

in the backlight housing. An additional benefit of this

configuration is an even distribution of light.

The ML4876 is optimized for portable applications where

high efficiency is critical to maximize battery life. The

high efficiency is achieved by a resonant scheme with

zero voltage switching.

BLOCK DIAGRAM

FEATURES

s

Backlight lamp driver with differential drive

s

Up to 30% lower power for same light output

s

Low standby current (< 10µA)

s

Improved efficiency (

»95%)

s

Allows all N-channel MOSFET drive

s

Low switching losses

s

Resonant threshold detection

s

Buck regulator uses synchronous rectification

LINEAR

REGULATOR

MASTER

BIAS

&

UVLO

VDD

VDD

GND

+

–

16V

B ON

B OFF

B SYNC OUT

DR3

DR1

DR1

ONE

SHOT

S

RQ

Q

NEG

EDGE

DELAY

Q

QR

S

Q

QR

S

+

–

0.1V

–

+

–

+

OSCILLATOR

CLK

RESONANT

THRESHOLD

DETECTOR

–

+

–

+

–

+

0.2V

0.5V

T

Q

Q

DR2

DR2

L RTD

L GATE 1

L GATE 2

LEA–

LEA OUT

FEA OUT

FEA+

FEA–

F ILIM

F GATE

LON

VREF

ON/OFF

HVDD

1

9

8

7

16

14

10

3

2

20

12

4

5

6

15

13

17

18

19

11

FEATURING

Extended Commercial

Temperature

Range

-20˚C to 70˚C

for Portable

Handheld Equipment

* THIS PART IS END OF LIFE AS OF JULY 1, 2000