Crystal part number selection

RE: Crystal part number selection

kadam — Mon, 27 Jan 2020 22:31:03 GMT

Dear sir,

Thank you for your reply.

RE: Crystal part number selection

ketiljo — Thu, 23 Jan 2020 09:00:01 GMT

Its says MAX load is 12.5 pF, meaning both will work. But again, ECS part will be better.

Ccap = CL * 2 - Cpin - Ctrace. Round down to the nearest value.

For a 12 pF crystal, the load caps should be 18 pF

For a 7 pF crystal, the load caps should be 12 pF

RE: Crystal part number selection

kadam — Thu, 23 Jan 2020 01:40:30 GMT

Dear sir,

As per nRF52840 datasheet, maximum load capacitance require is 12.5pF. So we select crystal ABS07-32.768KHz-T. We have follow equation as per nRF52840 datasheet and done calculation. For Stray capacitance we have follow 0.8pF per centimeter as per TI document(http://www.ti.com/lit/an/slla051/slla051.pdf). I have attached calaculation. Kindly suggest we have follow correct method or not. And please guide us it is better to use 7pF or 12pF.devzone.nordicsemi.com/.../How-to-Choose-Load-Capacitor-values-for-oscillator.docx

RE: Crystal part number selection

Kenneth — Tue, 21 Jan 2020 14:29:54 GMT

You can find the crystal requirements here:
https://infocenter.nordicsemi.com/topic/ps_nrf52840/clock.html?cp=4_0_0_4_3_3_2#unique_1547564644

As Ketil writes, it typically preferred to use a crystral with lower CL value.

If you choose a crystal that is out of specifications you will have issues maintain a link, since they will not be able to maintain synchronization.

RE: Crystal part number selection

kadam — Mon, 20 Jan 2020 22:16:43 GMT

Dear sir,

Thank you for your reply.

Please guide us for how 32.768KHz crystal is important for ANT protocol. How we can select crystal part number?

RE: Crystal part number selection

ketiljo — Mon, 20 Jan 2020 09:07:36 GMT

The crystal with the lowest CL value will draw less current and start faster. The ECS part have lower CL value than the the ABS part.