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I found a schematic and I want to reproduce it, in this part it has a crystal oscillator to run the processor, I design my PCBs with easyEda and print with JLCPCB. I never used a crystal oscillator, I assumed the capacitors are simple ceramic capacitors but when I upload my BOM and Pick and place to JLCPCB they only allow me to select a 12 pF crystal resonator, not a ceramic capacitor, is the schematic correct with crystal resonators instead of ceramic capacitors? In this case, what is its function?

enter image description here

Thanks in advance

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    \$\begingroup\$ 12pF crystal resonator 12 pF means that it is a capacitor, not a (crystal) resonator. Capacitors, crystals and resonators are different devices. This circuit is generally used to provide a clock signal to keep track of time (Real Time Clock). \$\endgroup\$ Jun 1, 2021 at 15:23
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    \$\begingroup\$ "12pf crystal resonator" could be referring to something like this: lcsc.com/product-detail/_TKD-3225-40M-12PF-10PPM_C337678.html \$\endgroup\$
    – ErikR
    Jun 1, 2021 at 16:27
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    \$\begingroup\$ Which component in your schematic is JLCPCB giving you trouble with, the capacitors C32 and C33 or Y2? \$\endgroup\$
    – ErikR
    Jun 1, 2021 at 16:34
  • \$\begingroup\$ The capacitors C32 and C33, I don't know what type I shoud choose \$\endgroup\$
    – mourazo
    Jun 2, 2021 at 6:37

2 Answers 2

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You want a multilayer ceramic capacitor (MLCC) that has a dielectric type NP0 (also called C0G).

The size and manufacturer are up to you. The voltage rating of most parts like this will be more than adequate (usually 50V).

If I look at the basic parts available from JLCPCB there are a number of choices in stock.

enter image description here

In this case your main choice is between 0402, 0603 and 0805 size.

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Ceramic is used for millions of things from insulators capacitors to resonators with the right mix of materials and geometry yet all behave differently. Thus a ceramic FM IF resonator is different from a ceramic capacitor, although most ceramics (albeit one Np0/C0G) have a slight piezoelectric effect.

Some with PZT added , much more than others used for BBQ igniters like the one I just salvaged from recycling trying to fix. 8(

There are many types of resonators : MEMs, ceramic, tuning fork, RLC and crystal. Don’t confuse them even if they have an equivalent RLCC equivalent circuit.

In all cases they can oscillate in parallel resonance by putting 2 caps in series with ground thus the values are reduced like all caps in series.

  • generally the C values chosen are twice the rated load capacitance.
  • If you do not reduce the input C value by the few pF of that CMOS type, then it will run maybe 10 ppm faster than expected.

Answer

  • the caps are added to tune the resonator to the factory design and swamp any parasitic ~1pF connections to be more accurate. Like tuning the tension on a guitar string.

    • But over a tiny range.

MEMs resonators are the most common choice for this frequency.

If you stated 24 pF for each capacitor for a 12 pF resonator or 21pF, 24 pF then it would be (more) correct. Y is the correct ref Des. For a resonator. C for a capacitor. Y was originally used for crystals, before MEMs were invented, just like Y1. ;)

Perhaps the trend now is for MEMs to include a semiconductor to classify it as an Oscillator and discrete MEMs are becoming obsolete. The Op should TAKE NOTE that it is cheaper now to simply buy an oscillator and then you don‘t have to worry about picofarads.. https://www.digikey.ca/en/products/detail/sitime/SIT1533AI-H4-DCC-32-768E/13520060

https://www.digikey.ca/en/products/filter/oscillators/172?s=N4IgjCBcoExgrABiqAxlAZgQwDYGcBTAGhAHsoBtEAZhgDoB2ANgYAIBrACQC8QTbGTABwcefGvRFdeAXRIAHAC5QQAVQB2AS0UB5DAFkCWPAFcATgRABfKySYoQmgCYqAtGEQQFyyCHGKAT3lLX2N0GyA

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  • \$\begingroup\$ tuning fork crystals are still very common at 32.768 kHz. only Murata seems to have MEMs at that frequency \$\endgroup\$ Jun 1, 2021 at 20:06
  • \$\begingroup\$ @Jasen Why aren’t you seeing the hundreds of MEMs parts that I see? digikey.ca/en/products/filter/oscillators/… \$\endgroup\$ Jun 1, 2021 at 22:18
  • \$\begingroup\$ Because I searched for 32.768 kHz resonators. \$\endgroup\$ Jun 1, 2021 at 22:25
  • \$\begingroup\$ Resonators are getting passé, when you can ignore parasitics and get better accuracy in the complete package and even make them programmable. \$\endgroup\$ Jun 1, 2021 at 22:48
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    \$\begingroup\$ Thanks for your response, I suppose that the component I shoud choose are ceramic capacitors. \$\endgroup\$
    – mourazo
    Jun 2, 2021 at 6:38

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