32 Khz square wave in Lieu of Crystal

[WesC]

In one of the customers current design implementations, they use a 32.768 kHz square wave in lieu of a 32.768 kHz crystal. they reduce the peak-to-peak amplitude and capacitor couple it to the crystal input, allowing the on-board crystal drive circuit to establish the DC bias.

 

Would the nRF52 part support this design approach, or does the part require a crystal to be used?

[Vincent Belaïche]

Dear Jared ,

We are also considering to make a design where the nRF52840 would use for the LFCLK and external 32,768kHz square wave source from an external RTC.
We would like to know from which nRF5SDK and SoftDevice versions this combination is supported, and whether legacy BLE SDK function can be used, or migrating to the newer nrfx_… API is mandated (just in case some of the legacy functions are not fully wrapped).

One more point of interest to us is how to handle the case of an external RTC that does not provide the 32kHz clock at reset. We are considering to configure the SDK to use the internal RC oscillator by default, and then switch to the HFCLK, stop LFCLK, enable external 32kHz, and then reconfigure LFCLK to be based on external 32kHz. Do you have any opinion on this approach ?

[Jared]

Hi Vincent Belaïche 

 

Could you create a new ticket for this question?

regards

Jared

[Vincent Belaïche]

Sure. Here is the new ticket.