nRF52840 external oscillator

[Nicolas Brunner]

Is it possible to put an external oscillator (e.g. TCXO) instead of a crystal for generating the 32 MHz of the nRF52840 ?

[bjorn-spockeli]

Hi Nicolas, 

I am assuming that you plan on sharing the external oscillator signal with other ICs in your design. Is this the case? Clock sharing is not recommended for the nRF52 series. The receiver is  very sensitive to noise on the reference clock and any noise here will affect the sensitivity of the receiver. Hence, we strongly recommend using a dedicated 32MHz crystal to ensure the performance stated in our product specifications.

Best regards

Bjørn 

[Nicolas Brunner]

I don't want to share the external oscillator. I just want to have a more accurate clock for the nRF52840, this is why i want to put a TCXO instead of a crystal.

[Mickael]

Hi Bjorn, 

we are going to try and this might be interesting to more people here!

Could you please specifiy if we should feed XC1 or XC2 pin (as in which is the input?) when doing this? 

Thank you,

Mickael

[bjorn-spockeli]

HI Mickael, 

You feed XC1 and XC2 should then, depending on what kind of signal your feeding into XC1, be one of the below:

• If low-swing sine: XC2 pin shall be grounded.

• If rail-to-rail: XC2 can be left open or grounded. Voltage requirement from GND to VDD_NRF.

[Mickael]

very clear! Thank you Bjorn

[abkirchhoff]

Mickael,

How did your attempt go at using a TCXO to feed XC1 on the nRF52840? Did it work reliably? If so, would you be willing to share the part number for the TCXO you used?

Thanks, Austin

[Mickael]

Hi Austin, I am getting boards back next week so will be able to test and give you an answer then. 

Dont hesitate to ping me if I forget. 

[abkirchhoff]

Mickael,

How are your new boards working?

Austin

[Dmitry]

This topic is very interesting for me too. Mickael, please don't forget to share your results with us, thanks.