Electronics > Beginners
Crystal load capacitance
TheHolyHorse:
Hi!
I'm working on a project which has a MCU(STM32F373) and I'm looking at crystals when I suddenly came across a crystal that didn't specify load capacitance it just said series. So I started doing some research but I still can't wrap my head around it.
This article https://ecsxtal.com/news-resources/video-learning/126-everything-you-need-to-know-about-quartz-crystal-resonators/133-understanding-load-capacitance says I can just ignore load capacitance when dealing with series resonance crystals.
So what can I just drop it in there and be done with it, no caps no nothing, it's just gonna work?? Sounds to good to be true.
Can someone fill me in?!
T3sl4co1l:
ST's appnote on crystal oscillators will be more beneficial:
https://www.st.com/content/ccc/resource/technical/document/application_note/c6/eb/5e/11/e3/69/43/eb/CD00221665.pdf/files/CD00221665.pdf/jcr:content/translations/en.CD00221665.pdf
It's a parallel oscillator; the specs of a series crystal will be slightly different (may not be the desired C and ESR leading to poor startup or an error of some kHz).
More importantly, ST's oscillators tend to be weak (low transconductance), so need a relatively high ESR / low C crystal. Shop for this. :)
Tim
TheHolyHorse:
Tanks for the link and reply, I'll absolutely follow your advice.
TheHolyHorse:
--- Quote from: T3sl4co1l on August 30, 2019, 12:23:32 pm ---More importantly, ST's oscillators tend to be weak (low transconductance), so need a relatively high ESR / low C crystal. Shop for this. :)
--- End quote ---
On a side note, would would be considered low load capacitance?
T3sl4co1l:
Your average crystal is something like, say, 8MHz, 100 ohms ESR, and 20pF specified loading. Or something around there. ST oscillators are more stable with like 200 ohms / 10pF.
Tim
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