UCC1973 datasheet(5/26 Pages) TI2

5 / 26 page

UCC1972/3

UCC2972/3

UCC3972/3

UDG-98154

*MODE

Output

Open Lamp

Detection

Error Amplifier Output

<1V

OFF

DISABLED

OPEN

DISCONNECTED FROM COMP

OPEN

1V< MODE< 3V

DISABLED

OPEN

CONNECTED TO COMP

CLOSED

>3V

ENABLED

CLOSED

CONNECTED TO COMP

CLOSED

VDD

20µA

–

1.5V

ERROR

AMPLIFIER

–

1.0V

7.0V

SYNC

OUT

RAMP

0.2V

OSCILLATOR

*MODE

SELECT

UVLO

4.0V/3.8V

3V REF

VREF

UVLO=1

3BIT

UP-DOWN

COUNTER

FROM MODE SELECT

OPEN LAMP DETECT

COMPARATOR

ZERO DETECT

COMPARATOR

UVLO

PWM

UVLO

OUTPUT OFF

(FROM MODE SELECT)

VDD

MODE

COMP

GND

OUT

BUCK

VDD

VBAT

18V

–

TO S3

OVER-VOLTAGE

CLAMP COMPARATOR

(ALWAYS OPEN ON UCC3972)

FROM

CLAMP

COMP

ICLAMP

9.0V

BLOCK DIAGRAM

Introduction

Cold Cathode Fluorescent Lamps (CCFL) are frequently

used as the backlight source for Liquid Crystal Displays

(LCDs). These displays are found in numerous applica-

tions such as notebook computers, portable instrumenta-

tion,

automotive

displays,

and

retail

terminals.

Fluorescent lamps provide superior light output effi-

ciency, making their use ideal for power sensitive porta-

ble applications where the backlight circuit can consume

a significant portion of the battery’s capacity. The

backlight converter must produce the high voltage

needed to strike and operate the lamp. Although CCFLs

can be operated with a DC voltage, a symmetrical AC

operating voltage is recommended to maintain the rated

life of the lamp. Sinusiodal voltage and current lamp

waveforms are also recommended to achieve optimal

electrical to light conversion and to reduce high voltage

electromagnetic interference (EMI). A topology that pro-

vides these requirements while maintaining efficient op-

eration is presented below.

APPLICATION INFORMATION

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