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Marcel Blindu
Marcel Blindu
Associate III
January 28, 2019
Question

Load Capacitors Crystals

How to prove if the selection of the load capacitors CL1 and CL2 for HSE and LSE Crystals is correct?

Maybe with oscilloscope?

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    1 reply

    Mon2
    Mon2
    Senior III
    January 28, 2019

    If your code runs then you are good to go. You can review the example caps used in the ref design and also contact the crystal manufacturer for their feedback on the recommended loading cap values. Often the caps are around 8pf - 25pf and not super critical on their value. Purchase a few different values to experiment and keep the values the same for both legs of the crystal. If really concerned then you can just skip and source a crystal oscillator which is guaranteed to always power up and oscillate. Be sure that pin # 1 (OE) is strapped HIGH to enable the oscillator. Review the datasheet from ST on how to mate an oscillator vs. crystal. With the oscillator, no loading caps are required.

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