Hi, I know there have been several topics created about this, but I was unable to find a clear answer. I often hear that 500ma is the maximum that can be drawn (due to the fuse on the USB VCC line), but looking at the at the datasheet for the Atmega16U2, 200ma is the absolute maximum rating for it…

Maximum Current Draw from Arduino Mega 2560

CrossRoads February 15, 2013, 2:27am 11

UVCC powers the on-chip 3.3V regulator. VCC and Avcc connect to +5V and power the rest of the chip.
See page 3 of the datasheet

More docs here

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