low frequency 32Khz XTAL

RE: low frequency 32Khz XTAL

Kaja — Thu, 01 Aug 2019 05:37:42 GMT

Please make a new case on DevZone, to get an engineer assigned to your question.

Best regards,
Kaja

RE: low frequency 32Khz XTAL

KariMa3 — Tue, 30 Jul 2019 10:25:03 GMT

Is it allowed to use nonsymmetric capacitors to get more accurate 32k ? With 2x10pF we run some 35ppm too fast and 2x12pF the clock is 10ppm slow. We could use non standard 11pF capacitors or use 10pF+12pF to get very accurate clock. Is there any recommendation on this ?

RE: low frequency 32Khz XTAL

Nguyen Hoan Hoang — Mon, 24 Sep 2018 16:32:17 GMT

try the caps in the range of 8pF instead. It is approx calculated as 2 * Cl - 4pF which is 8pF in your case.

RE: low frequency 32Khz XTAL

Kenneth — Thu, 20 Sep 2018 18:18:39 GMT

If you set LF accuracy to NRF_CLOCK_LF_ACCURACY_500_PPM when enable softdevice does it work then?

I think either the frequency is wrong or possible some hardware issues (e.g. soldering issue?).

RE: low frequency 32Khz XTAL

johananh — Thu, 20 Sep 2018 13:40:24 GMT

We use XTAL with 6 pf CL.

I tried C11 C12 10pF without results.

Thanks

Johanan

RE: low frequency 32Khz XTAL

Kenneth — Thu, 20 Sep 2018 13:24:06 GMT

Hello,

If you set LF accuracy to NRF_CLOCK_LF_ACCURACY_500_PPM when enable softdevice does it work then?

If yes, then likely the problem here is the series capacitors on the crystal, you may want to increase them yes. For instance if you are using a 32.768kHz crystal with CL=9pF, then the series capacitors (C11 and C12) should be 12pF:
http://infocenter.nordicsemi.com/topic/com.nordic.infocenter.nrf52810.ps/ref_circuitry.html?cp=2_2_0_6_2

What is the CL for the 32.768kHz crystal you are using?

Best regards,
Kenneth