View Full Version : Crystal Requirements

11-11-2006, 04:42 AM
·Are there any caveats to choosing an external·crystal for the Q-44 package...? We attempted to use a 5MHz / 20pF but the smd package of the prop did not seem to be agreeable whereas the 40 pin DIP package had no problems.....?

thanks in advance.....

11-11-2006, 04:59 AM
We've not noticed any such problems, and by design they shouldn't exist. Usually, a sagging power supply or lack of an external capacitor between VSS and VDD cause problems that look like that. Do you have adequate decoupling (1uF) on the -Q44 board, and is the power supply a stable 3.3V? Just checking.

BTW, the crystal oscillator provides much more capacitive loading to the crystal than package-related parasitics introduce, so I'm thinking there was some other problem.


Chip Gracey
Parallax, Inc.

Post Edited (Chip Gracey (Parallax)) : 11/10/2006 10:13:03 PM GMT

Phil Pilgrim (PhiPi)
11-11-2006, 07:56 AM
Also, if you're prototyping the Q44 circuit with a non-soldermasked PCB, make sure the crystal can doesn't touch any traces. Even with soldermask, I recommend a crystal insulator.