Sharing a 32kHz crystal between 2x nRF52840

[Eggz]

We plan to use 2x nRF52840 in our new product design, and want to know if they can share a common 32kHz crystal. From the following discussion it appears to be possible, but we want to be sure before moving on:

https://devzone.nordicsemi.com/f/nordic-q-a/41280/nrf52840-output-the-32-768khz-clock-on-any-gpio-in-spi-communication/160524#160524

Is it simply a matter of setting up the LFCLKSRC register correctly? Any guidelines are appreciated. Thanks!

[Simonr]

Hi Egil

Please check out our whitepaper on Sharing crystal with an MCU.

Best regards,

Simon

[Eggz]

Hi Simon,

Thanks - very informative whitepaper.

In our case we have 2x nRF52840, so one of them will have to control the crystal. Does nRF52840 have power up as input pin? The whitepaper covers nRF24L01 which didn't have this option.

Best regards,

[Simonr]

Hi Egil

Sorry, but can you please explain what you mean with "power up as input pin". If you mean an enable pin like on the nRF9160, then no.

Best regards,

Simon

[Eggz]

Hi Simon,

Thanks! I'm afraid I'm not familiar with the nRF9160. I was referring to the last sentence in the conclusion in the whitepaper, where nRF24L01 is said to have this limitation. The whitepaper recommends us to control the LF crystal with the external MCU & to feed the nRF24L01. In our case we have 2x nRF52840 and no external MCU, so the crystal must be controlled by one of them, which may lead to increased power consumption.

Best regards,

[Simonr]

Hi Egil

One of the nRF52840s will have to stay in power on mode but should be able to run the crystal from the Low-power mode. So yes, there will be an increased power consumption on one of them, but not by too much I think.

Best regards,

Simon