Power Stage Controllers drive transistors in applications like DC to DC converters, power factor correcting circuits, motor drivers, etc. Atmel describes the basics of their PSC equipped AVRs:
This application note is an introduction to the use of the Power Stage Controllers (PSC) available in some AVR microcontrollers. The object of this document is to give a general overview of the PSC, show their various modes of operation and explain how to configure them. The code examples will make this clearer and can be used as guide for other applications. The examples are developed and tested on AT90PWM3.