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diva-eng / diva-card

Raspberry Pi 2040 based development board/card
MIT License
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Choice of 100 ohm resistor for crystal oscillator #1

Closed DLehenbauer closed 2 months ago

DLehenbauer commented 3 months ago

I was wondering how you chose the value of 100 ohms for the resistor (R10)?

I am working on a design using the same parts (RP2040 and X322512MSB4SI oscillator). However, I kept the 1K resistor from the reference design.

My prototype works but requires a firmware workaround to increase the startup delay to 16ms or more.

# On tested sample, 8ms was intermittent and 16ms was reliable.
# 64ms provides a large tolerance.
add_compile_definitions(PICO_XOSC_STARTUP_DELAY_MULTIPLIER=64)

I thought maybe you ran into the same issue and reduced the value of R10 to compensate?

r1cebank commented 2 months ago

The reference design was using a different capacitor I recall and since we chose a different oscillator the feed resistor has also been adjusted to that oscillator. I do not recall what was the actual calculation done but it was based on the oscillator ESR https://www.lcsc.com/datasheet/lcsc_datasheet_2403291504_YXC-Crystal-Oscillators-X322512MSB4SI_C9002.pdf and existing designs using the same part. Hope this helps

DLehenbauer commented 2 months ago

I appreciate the response. Sounds like you got it right on the first try. Thanks!