External Crystal Oscillator for nRF51422 for custom PCB

[Ehsan]

Hi,

I am designing a custom PCB using the nRF51422. I want to include an external 16 MHz crystal oscillator to use as X1 according to the reference layout for custom PCBs. The crystal I have has a capacitance of 15pF instead of the 8pF crystal used in the reference layout. Would that make a difference?

Also, my crystal has an accuracy of +-50ppm compared to the 40ppm of the recommended design. Would my crystal be sufficient for bluetooth communication?

Regards, Ehsan

[Petter Myhre]

Firstly, you should check Chapter 8.1.2 in nRF51422 product specification.

There you can see that the maximum frequency tolerance for BLE is +-40 ppm, so +-50 ppm is not recommended.

Other than that you should choose a crystal that is less than the maximum values of C0, CL, ESR and drive level.

This tutorial may also be of interest.