Capacitor selection

Derek Prost · Guest

Could someone tell me what is the best capacitor type to use for the
xtal oscillator pins i.e. OSC1 and OSC2

Guest · Posted: Fri Jan 23, 2004 2:54 am

Hello Derek Prost,

Please google for e.g. 'PIC18FXX2 datasheet' or go to Microchip website directly and download the wanted datasheet.
After that, you have to look at the datasheet under 'Oscillator Configuration'. There you can see what capacitor your PIC need.

Hope to help you
73 Sven

wedilo · Joined: 16 Sep 2003 Posts: 71 Location: Moers, Germany

Hello Derek Prost,

Please google for e.g. 'PIC18FXX2 datasheet' or go to Microchip website directly and download the wanted datasheet.
After that, you have to look at the datasheet under 'Oscillator Configuration'. There you can see what capacitor your PIC need.

Hope to help you
73 Sven

wedilo · Joined: 16 Sep 2003 Posts: 71 Location: Moers, Germany

Ooops now it's twice. Sorry Embarassed

Can't delete the first one with guest status.

73 Sven

Derek Prost · Guest

I am not talking about the value of the capacitor. I want to know what
type ie. ceramic etc. Thanks.

rwyoung · Joined: 12 Nov 2003 Posts: 563 Location: Lawrence, KS USA

I wouldn't use anything lower "quality" than X7R. COG or NPO should give you the best results with reguard to stability vs. temperature.

If this is just a one-off design and will live on your benchtop only, then just about any ceramic will work OK. But don't expect much better than 20% accuracy under ideal conditions with Y5V or Z5U type capacitors.

And just to cover the bases, if you need better than 1% accuracy you should be looking at ceramic resonators and crystals. Generally the oscillator accuracy/stability increases in this order:

Internal, External RC, Ceramic Resonator, Crystal, External Oscillator (assuming you buy a high-end unit)

But depending on how you configure things and which exact part you are using, the "Internal" oscillator option may be more stable than the "External RC" option.
_________________
Rob Young
The Screw-Up Fairy may just visit you but he has crashed on my couch for the last month!

snoopy · Guest

Hi

Look at this PDF file from Calchip, the beginning pages will help
you to understand which cap are the best.

In your case NPO or COG is better.

http://www.calchip.com/pdf/gmc.pdf