Capacitors needed with a crystal?

I understand 30pF capacitors are needed to connect a 11.05Mhz crystal to the MCU as per my text book.

But the nearest capacitors I have is 47pF or 10pF.

Why do we need capacitors with crystal (I assume for smoothing purposes) the MCU works fine without them?

Would I get away with using capacitor values other than 30pF?

Many thanks

AceOfHearts said:

I understand 30pF capacitors are needed to connect a 11.05Mhz crystal to the MCU as per my text book.

But the nearest capacitors I have is 47pF or 10pF.

Why do we need capacitors with crystal (I assume for smoothing purposes) the MCU works fine without them?

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No, they are an essential part of the oscillator circuit.

Would I get away with using capacitor values other than 30pF?

Click to expand...

Yes, it's in no way critical, either 10pF or 47pF should work fine - as it's a higher frequency crystal I'd probably go with 10pF myself given those choices.

Nigel Goodwin said:

No, they are an essential part of the oscillator circuit.



Yes, it's in no way critical, either 10pF or 47pF should work fine - as it's a higher frequency crystal I'd probably go with 10pF myself given those choices.

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Thanks Nigel for the very helpful reply.

Regards.

The value of the capacitors will affect the frequency, but probably not enough to be noticed unless you need very high accuracy.

If the frequency needs to be adjusted, a range of a few ppm can be achieved with a trimmer capacitor in parallel with one of the capacitors.