I'm designing a tiny custom board that will use the same microprocessor and bootloader as the real Leonardo. On a UNO type board I made a while ago I used Digikey resonator part: h**p://www.digikey.ca/product-detail/en/CSTCE16M0V53-R0/490-1198-1-ND/584635 that works great. I've seen the Leonardo schematic that uses a crystal with two external capacitors. Any idea if a resonator with built in 15pf caps will work on the bootloader thats is in the Arduino software? I'm hoping to load it into the Atmel chip using the USBtinyISP programmer.
You might be able to get something onto the Atmega32u2 with a USBtiny (the USBtiny has a Crystal), but I doubt you will be able to use the Atmega32u2 with USB with the resonator as a clock source for the USB2TTL.
The key parameter is the frequency tolerance, which must be within +/- 500ppm of the USB specification. See http://www.cypress.com/?docID=26060 and http://www.ti.com/lit/an/slla122/slla122.pdf.
It will work with or without the added capacitors. The added capacitors will slow down the oscillator a little.
In general, you should try to use a crystal, for its better accuracy / stability. The price difference is minor and there are many smd crystals.
Just a quick update that the resonator on my Atmega32u4 is allowing me to upload sketches over USB. I wasn't expecting it to but it does. My 2nd rev has a crystal like all the others I've seen. I guess I just lucked out on this one.
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