32MHz crystal frequency calibration

[prabhakar kumar]

Dear HW engineer,

I have ordered a few custom boards with nRF52820. As recommended by the datasheet, I have used 12pF load capacitors for both HF (32MHz) and LF (32kHz) oscillators.
However, the boards developed in past with nRF52811 accept 12.5pF of capacitance which is very hard to find.
My question is how do we cope with the variation of the sub-pF capacitance in manufacturing?

Thanks  and regards

Prabhakar

[ketiljo]

If you're using a relatively accurate crystal, you should be fine by calculating the cap value as Ccap = CL *2 - Cpin, where Cpin = 4 pF.

The frequency tolerance for BLE is +/-40 ppm.