Design goals for cold cathode fluorescent lamp (CCFL) converters for laptop or portable applications include small size, high efficiency, and low cost. The UCC3972/3 CCFL controller provides the circuit blocks necessary to achieve a high efficiency CCFL backlit power supply in a small footprint 8-pin TSSOP package.
BiCMOS controllers typically consume less than 1mA of operating current, improving overall system efficiency compared to bipolar controllers that require 5mA to 10mA of operating current. The number of external components is minimized and system costs are reduced with features such as integrated feedback controlled PWM drive stage, light on protection, startup delay and synchronization circuit between step-down stage and push-pull stage.
The UCC3972/3 includes an internal shunt regulator that allows the unit to operate at input voltages from 4.5V to 25V. The unit supports the operation of analog and externally generated low frequency dimming modes. UCC3973 adds a programmable voltage clamp at the BUCK pin. This function can be used to protect the transformer from overvoltage during startup or when the light is on. When overvoltage is detected, the transformer voltage is controlled by reducing the duty cycle.
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
● Synchronized to PWM Frequency External Resonant Tank
● 8 Pin TSSOP and SOIC Packages Available
● Internal Voltage Clamp Protects Transformer from Over-voltage (UCC3973)
Typical application circuit
Connection diagram
Block diagram
