Crystal Oscillator in Teensy 2.0

M

MStankovich

New member
Hello all,

What is the exact model number (manufacturer and number) of the 16MHz oscillator used with the ATMega32U4 in the Teensy 2.0? I am trying to build an ATMega32U4-based board for my own project, but the datasheet is not very specific about stray capacitance which makes it difficult to choose the right oscillator and load capacitors to ensure that my circuit works properly. Because my project needs to be completed on a relatively short timescale, I would prefer to use a solution that is known to work (i.e. the Teensy 2.0 oscillator) than to try and select parts myself that might not be compatible with each other. Thanks in advance.

Michael Screen Shot 2022-10-27 at 1.12.29 PM.png
 
I've always used around 18pF crystals and 18pF or 22pF load caps on ATmega's without issue. I believe its not super critical. Note the load caps are effectively in series from the crystal's viewpoint, so two 18 or 22pF load caps provide 9--11pF of load and the chip input capacitance provides some more, and there's also stray capacitance of the traces. Keep the traces between chip and crystal short and away from noise sources (power traces), especially if using the low-power modes for the oscillator.

The 32U4 datasheet suggests load cap values in the range 12pF to 22pF. It also says I/O pins are 10pF, but doesn't specifically indicate the XTAL pins capacitance, but its likely to be similar as the XTAL pins can be configured as GPIO and will have a similar pad section on the chip.
 
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