Crystal selection for Xmega

Go To Last Post
5 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi all,

I've done several designs using standard AVRs but it's time to do my first with the ATxmega128A1.

Regarding crystal selection, what is suitable crystasl load capacitance (CL) for a 16 MHz together with the ATxmega128A1? Standard values for crystal CL is 8pF, 9pF and 10pF.

In previous designs I've also used external caps to add extra CL, 22 pF is standard value there.

So, what should I choose as crystal CL for a ATxmega128A1?

Kind regards
Bjorn

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

You do not really need a high speed crystal for the xmega, especially if you use a 32768Hz watch crystal for the RTC.

Otherwise, you are just going to use similar CL values as with the mega.

David.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Nothing has been significantly changed since then. See Table 7-5. Oscillator frequency range selection in the XMega A Manual for suggested cap values vs crystal frequency.

Warning: Grumpy Old Chuff. Reading this post may severely damage your mental health.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thanks for your replies!

I notice that in table 7-5 C1/C2 is recommended to be 10 pF, which in somewhat lower then previous 22 pF.

I guess for the internal CL for the crystal it is not much difference between 8, 9 or 10 pF so anyone would do.

/Bjorn

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I'm running at 32MHz, I'm revisiting the crystal selection in my design. Is it better to use a lower speed crystal and high PLL muiltipler (example: 2Mhz with PLL at 16) or a high speed crystal and low PLL multiplier (example: 16MHz with PLL at 2)?