I am designing a custom ATmega32U4 PCB with the following specifications:
- Should run at 3.3V @8MHz.
- Can be powered by the USB or external battery.
- Relies on the inbuilt bootloader for programming via Atmel's FLIP.
Going through the already available proto-boards in the market, I found the following products as a reference for my design:
On further analysis, I decided that the Adafruit Feather 32u4 Basic Proto is closest to my design idea, so I kept the schematic as a reference.
I have the following questions:
- The VBUS pin is not used as a supply source for the µC and is only for a reference voltage. Correct?
- For a 3.3V supply, the 5V from the USB can be regulated to 3.3 and the UVCC pin can be left unconnected. Correct?
- According to the ATmega32U4 datasheet, the UCAP pin must be connected to a 1µF capacitor. But if you look at the Adafruit schematic, it is connected to the 3.3V source and decoupled using a 10µF cap. Can anyone explain why?
Thanks in advance!