SparkFun-32u4 power

Are we talking about this product?

I just received this part and am trying to figure out the power wiring. The breakout pins called “VCC” and “5V” I think are tied together and map to what Atmel calls “VCC” and “AVCC”?

Correct, on the AVR chip “VCC” and “AVCC” are seperate pins, but are often connected together on the pcb.

The breakout pin called “3.3V” is the output of the onboard 3.3V regulator?

It’s connected to it, yes. It’s not really a breakout pad intended to connect wire to. But it is intended as an easy access voltage selection option. A solderjoint is easy to remove/reconfigure, yet also static and more resiliant than a switch or jumperpins which can be accidentally pulled/flipped.

The PDF schematic ( … ut-v11.pdf) shows an SJ1 “Power Select”. I don’t see that physically on this board. Where is this?

If your board looks different from the pictures on the product page, then I suggest you make a picture and show what’s on yours. On the product page I clearly see solderjumper pad in the forward corner showing the 5 volt side containing a solderbridge. If you would remove that, and solder the middle to the 3.3 volt side then the microcontroller would operate on 3.3 volt basis. It still gets the 5 volt from the USB connector though, or whatever you connected to the 5 volt input.

I just will provide 5V to the “5V” and “VCC” pins.

Thank you.

No need to additionally connect VCC, as the solderjumper is placed already.

The USB connector is followed by a PTC-fuse before it is labeled as 5 volt in the schematic. So you won’t have that protection if you power it at the 5 volt point with your own powersupply. Also, you loose the serial port connection if you don’t use the USB connection. Quite a drawback in the testing and developing phase.