Arduino Due: ATSAM3X8E 12MHz Oszillator

Hey,

I noticed that the ATSAM3x8E used for the arduino due uses an 12MHz crystal with a load capacitance of 20pF and two 22pF external capacitors.
The datasheet specifies an allowed crystal capacitance load of 12.5 to 17.5 pF and external caps < 10pF (Datasheet p.1397). I’m about to do a custom version of the due and wanted to ask why this might be and if it could cause problems to stick with the Arduino schematic.

Any thoughts?

Thanks & Greetings

Im curious on this too...having a hard time finding a suitable crystal.

The SAM3X datasheet says max ESR of 80ohms. Its tricky to find a crystal with 80 ohm ESR, and rated for -40* operating temperature.

What would go wrong if I used a 12mhz crystal with an ESR of 100ohms?

The load capacitance is a little confusing too....I was always under the impression that load capacitance of the crystal didnt really matter with respect to the microcontroller itself....just as long as you used the appropriate capacitors on the board according to the crystal's data sheet...

http://www.mouser.com/ProductDetail/AVX/CX3225GB12000H0KPSC1/?qs=sGAEpiMZZMsBj6bBr9Q9afyHw99U5mruupNyPHlUYsp%2FdTfACl1k9g%3D%3D

http://www.mouser.com/ProductDetail/ABRACON/ABM8AIG-12000MHZ-12-2Z-T3/?qs=sGAEpiMZZMsBj6bBr9Q9ad1mSHUxq96eTV7Z6lGhvGjHlr2zeyhjCg%3D%3D

Either of those look ok?

Digikey lists 10 PAGES of 12MHz crystals with ESR <80 and -40 operation…

Also, since the sam3x has fancy clock circuitry, you don’t necessarily need a 12MHz crystal to get a 12MHz clock…

westfw:
Digikey lists 10 PAGES of 12MHz crystals with ESR <80 and -40 operation…

Also, since the sam3x has fancy clock circuitry, you don’t necessarily need a 12MHz crystal to get a 12MHz clock…

Ah I should have been more clear…

I need a smaller package crystal. Something in a 3.2mm x 2.5mm package.

I only found those two I listed above. One has an ESR of 150 ohms, and the other has an ESR of 100 ohms, and a load capacitance of 12 pF.

What are the “dangers” of using a crystal slightly outside the range on both ESR and load capacitance?

I would think I definitely want to use the external clock, because im doing some timing critical stuff like RS232, CANbus, and SPI…?

I guess I can redesign the board to use a larger footprint crystal, but it would be nice if I could get away with using one of those smaller crystals (that are slightly outside of the ESR and load capacitance range).

Yes it is very tricky to find a crystal with such characteristics. I have been searching for more than an hour in farnell, digikey, mouser, and Rs and cant seem to find it.

Any links to the buy?

ty

I have found this although its 18pF.

https://www.pericom.com/assets/Datasheets/FL.pdf

How important really are those specs?