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)

DESCRIPTION

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

a notebook computer or portable application include small size, high efficiency,

and low cost. The UCC3972/3 CCFL controllers provide the necessary

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 integrating

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.