Crystal loading capacitors
This is a split off the KISS Board Eval thread, but is definitely its own topic.
I have had plenty of designs using 10ppm crystals get 150ppm out because the loading capacitors aren't quite right. This really becomes an issue when you have a ground plane (which is a very good idea) because the loading caps then parallel/add to the ground-plane caps, so the frequency can wind up very wrong.
I don't have much choice there because the loading caps are internal to the P2.
What are the internal loading caps when you select 15pf? The correct loading caps for a crystal often vary somewhat depending on what else is on the board, trace thickness, distance to ground plane, etc. Crystals being 150ppm off because of loading caps that don't account for board geometry is a problem on another product I'm working on now.
If somebody decides to use a smartpin counter, along with some software, as an RTC for example, and they choose a high-precision crystal for it, how would they go about tuning caps for the end board design within DVT?