UCC28C45P

Introduction

UCC28C45P is a current-mode pulse width modulation (PWM) controller specifically designed to operate in low power applications, such as automotive, consumer, industrial and communications systems. The UCC28C45P has been designed with a set of features to limit the losses, reduce design time and cost. Such features include low operating current (8uA), fast startup time, load well tolerances, a synchronizing signal, an active current limiting protection, an adjustable current limit and a selectable frequency mode. This document will describe the application field and working principle of the UCC28C45P.

Application Field

UCC28C45P is mainly used in automotive, consumer, industrial and communication systems for providing efficient, low-power and stable supplies for loads. It is designed for applications such as off-line AC-to-DC or DC-to-DC high-efficiency converters, with an adjustable switching frequency from 100kHz to 500kHz, and with a current peak mode which can achieve high power levels with minimum ripple. It is mainly used for battery chargers, switch mode power supplies (SMPS), DC-DC converters or any other current-mode PWM applications.

Working Principle

UCC28C45P mainly uses PWM technique to regulate the output voltage. UCC28C45P operates in fixed/variable/off frequency modes. In fixed/variable frequency modes, the output frequency is determined by the maximum and then by the minimum Duty cycle, while in the off Frequency mode, the output frequency is dependent on the load conditions. The adjustable current limit feature is implemented with a current-mode control loop. This loop compares the voltage drop (VDS) across the current sense resistor with an embedded reference. A comparator is used for this purpose, when the voltage surpasses the reference, it indicates an overtemperature condition or an overload from the output and then the controller will immediately shut down the power switch.

UCC28C45P includes a couple of protection features. The Automatic Shut Down prevents the part from operating while out of the synchronizing range, while the automatic protection circuit will reduce the current limits if thermal shut down occurs as a fault protection. These can help to avoid short circuit and overheating of components and also reduce power supply design requirements.

Conclusion

UCC28C45P is a current-mode PWM controller specifically designed to operate in low power applications. It is ideal for off-line AC-to-DC or DC-to-DC power supplies, battery chargers, SMPS, DC-DC converters and other current-mode PWM applications. It has adjustable frequency, current peak mode with minimum ripple and adjustable current limit features, as well as a set of other protection features ensuring a stable, reliable and efficient power supply.