AVRPi-328 Schematics and datasheets
Here are the schematics of the AVRPi-328 board and datasheets for those components on the board that may matter to you.
AVRPi-328 schematics: AVRPi-328 schematics
ATmega328p datasheet: ATmega328p datasheet (summary)
Power
The AVRPi-328 can be powered from the 3V3 line on the Raspberry Pi GPIO pins.
In this Adafruit article, the RT8020 1V8/3V3 buck converter is mentioned for the Raspberry Pi. While it's likely that component, it's unofficial information.
3V3 Power from Pi A+/B+/2: RT8020