1 Features

1• Prebiased Start-up

• Synchronous Rectifier Control Outputs With

Programmable Delays (Including Zero Delay

Support)

• Voltage Mode Control With Input Voltage Feed-

Forward or Current Mode Control

• Primary or Secondary-Side Control

• 3.3-V, 1.5% Accurate Reference Output

• 1-MHz Capable Switching Frequency

• 1% Accurate Cycle-by-Cycle Overcurrent

Protection with Matched Duty Cycle Outputs

• Programmable Soft-Start and Hiccup Restart

Timer

• Thermally Enhanced 4-mm × 4-mm QFN-20

Package and 20-pin TSSOP Package

2 Applications

• Half-Bridge, Full-Bridge, Interleaved Forward, and

Push-Pull Isolated Converters

• Telecom and Data-com Power

• Wireless Base Station Power

• Server Power

• Industrial Power Systems

3 Description

The UCC28250 PWM controller is designed for high

power density applications that may have stringent

prebiased start-up requirements. The integrated

synchronous rectifier control outputs target highefficiency

and high-performance topologies such as

half-bridge, full-bridge, interleaved forward, and pushpull.

The UCC27200 half-bridge drivers and

UCC2732X MOSFET drivers used in conjunction with

the UCC28250 provide a complete power converter

solution.

Externally programmable soft-start, used in

conjunction with an internal prebiased start-up circuit,

allows the controller to gradually reach a steady-state

operating point under all output conditions. The

UCC28250 can be configured for primary or

secondary-side control and either voltage or current

mode control can be implemented.

The oscillator operates at frequencies up to 2 MHz,

and can be synchronized to an external clock. Input

voltage feedforward, cycle-by-cycle current limit, and

a programmable hiccup timer allow the system to

stay within a safe operation range. Input voltage,

output voltage and temperature protection can be

implemented. Dead time between primary-side switch

and secondary-side synchronous rectifiers can be

independently programmed.