Trying to understand Sparkfun Pro Micro design

Kindly offer me some help here :slight_smile:

I am studying the sparkfun arduino pro micro (hate their naming confusion). This is an ATMEGA32U4 based board that eliminates the need for a USB TTL adapter. I like it. It’s simple enough that I might be able to replicate in my design. I do have a bunch of questions though:

  1. The EN pin on the MIC5219 chip. If USB UVCC is 5V, and RAW is say 12V, then RAW will pull EN high enough to output, right? If yes, then this 5V is connected to the USB UVCC, which is only nominally 5V. Then there will be some excessive current flowing back and forth between the USB port and the regulator, am I correct? Any problems with this? Arduino Micro (not designed by sparkfun) has a more complex voltage selector.

  2. What’s the use for 3 capacitors on the voltage regulator, 10uF, 1uF and 0.1uF? Is it to filter out high-freq ripple with smaller caps and stabilize output with larger caps? Arduino Micro only has 2uF and 0.1uF.

  3. What is the capacitor doing on UCAP on the 32U4? I might be able to answer that after reading the spec sheet.

  4. Did anyone design a board based on 32U4 and or this pro micro design? Any tricks and pitfalls?

Thank you!

Pro-Micro-v11-5V_B.pdf (65.2 KB)

I designed this with lots of forum input, especially fm.
Think I have 1 bare board left from a 50-lot. Never assembled one myself, but many others did.