UCC1972/3

UCC2972/3

UCC3972/3

DESCRIPTION

Design goals for a Cold Cathode Fluorescent Lamp (CCFL) converter used

in a notebook computer or portable application include small size, high effi-

ciency, and low cost. The UCC3972/3 CCFL controllers provide the neces-

sary circuit blocks to implement a highly efficient CCFL backlight power

supply in a small footprint 8 pin TSSOP package. The BiCMOS controllers

typically consume less than 1mA of operating current, improving overall

system efficiency when compared to bipolar controllers requiring 5mA to

10mA of operating current.

External parts count is minimized and system cost is reduced by integrat-

ing such features as a feedback controlled PWM driver stage, open lamp

protection, startup delay and synchronization circuitry between the buck

and push-pull stages. The UCC3972/3 include an internal shunt regulator,

allowing the part to operate with input voltages from 4.5V up to 25V. The

part supports both analog and externally generated low frequency dimming

modes of operation.

The UCC3973 adds a programmable voltage clamp at the BUCK pin. This

feature can be used to protect the transformer from overvoltage during

startup or when an open lamp occurs. Transformer voltage is controlled by

reducing duty cycle when an over-voltage is detected.

BiCMOS Cold Cathode Fluorescent Lamp Driver Controller

FEATURES

• 1mA Typical Supply Current

• Accurate Lamp Current Control

• Analog or Low Frequency Dimming

Capability

• Open Lamp Protection

• Programmable Startup Delay

• 4.5V to 25V Operation

• PWM Frequency Synchronized to

External Resonant Tank

• 8 Pin TSSOP and SOIC Packages

Available

• Internal Voltage Clamp Protects

Transformer from Over-voltage

(UCC3973)

SLUS252A - JANUARY 2000

3

8

6

5

VBAT

4

2

1

7

VDD

GND

MODE

COMP

BUCK

OUT

FB

C7

0.1

µF

D1

R10

R11

Q3

C5 0.1

µF

L1

68

µH

R6 75

Ω

Q2

R2 1k

T1

C6 27pF

LAMP

HV

LAMP

LV

R3 68k

D2

R5 10k

R4 750

ANALOG

DIMMING

D

LFD

R

0V-5V LOW FREQUENCY CONTROL SIGNAL

C4 33nF

LOW FREQUENCY DIMMING

C2

1

µF

R1

1k

Ω

C1

6.8

µF

SYSTEM VOLTAGE

(4.5V TO 25V)

C3

1

µF

UCC3972

UCC3973

NO INTERNAL VOLTAGE CLAMP

INTERNAL VOLTAGE CLAMP LIMITS TRANSFORMER

VOLTAGE AT START-UP OR DURING FAULT

UCC3972/3

TYPICAL APPLICATION CIRCUIT

UDG-99154