[layout] 32KHz crystal opposite side of the nrf (via)

RE: [layout] 32KHz crystal opposite side of the nrf (via)

butch — Fri, 27 Oct 2017 16:07:53 GMT

RK: you mean use a frequency counter while running, and swap out various capacitances ?

Tizana: move your vias to the left to shorten the traces. I don't think there is anything inherently wrong with using vias. Using vias and the back side xtal, you could make your traces shorter than a front side design.

Doesn't the stray or parasitic capacitance depend on the length of traces and distance to ground? I think standard advice is to keep the area around the crystal free of ground plane. You don't show your ground connections or ground plane, which could be important.

Unless you are intending to keep real time (same as someone else's clock) it is not critical. If your design only works with itself, then the fact that all your boards are identical means their RTC clocks will have the same error.

RE: [layout] 32KHz crystal opposite side of the nrf (via)

RK — Thu, 15 Jun 2017 03:39:29 GMT

trial and error after you've built one.

RE: [layout] 32KHz crystal opposite side of the nrf (via)

Tizana — Thu, 15 Jun 2017 03:38:33 GMT

adding the load capacitance mean the Cstray will increase ? is that what you mean ?

so i have to adjust the cap C9 and C8 ? how can i determine the Cstray ?

RE: [layout] 32KHz crystal opposite side of the nrf (via)

RK — Thu, 15 Jun 2017 03:35:28 GMT

The vias will add extra load capacitance, so you'll have to experiment to adjust the load caps (probably downwards) to get the right frequency. But as long as the traces are short and the vias large enough, it shouldn't be that bad.