RTC crystal calculation

[Kim_JE]

Hi,

We are in the process of changing the 32.768 kHz RTC crystal in an existing product and require additional data to verify the electrical properties of the crystal.

For the oscillator calculations, I need the following parameters:

• Minimum gain margin

• Maximum critical gain margin

I have reviewed the datasheet but was unable to locate this information. Could you please provide the relevant specifications or application guidance?

Best regards,

Kim

[Kenneth]

Hello,

There is no need for you to know these details, as we have specific in the datasheet the specification of the external crystal oscillator must meet to work reliably with the nRF52840. The parameters for the 32kHz crystal is listed here:
https://docs.nordicsemi.com/bundle/ps_nrf52840/page/clock.html#ariaid-title39 

So make sure to choose a crystal part number that meet those criteria.

Kenneth

[Kim_JE]

Hi Kenneth,

Thank you for your reply.

For our other products, we rely on detailed calculations to ensure that the circuits function as intended, and I believe the same approach would be beneficial for the RTC oscillator. However, since this information is not readily available, I will follow your recommendation and proceed by reviewing the specification you provided and comparing it with the crystal I consider suitable.

Thank you again for your assistance.

Best regards.

Kim