RAK5010 XTAL frequency too high

Cellular Boards RAK5010
1

Issue: The expected frequency of XTAL crystal oscillator (connected to NRF52840) is 32768 Hz but we measure constantly ~32780 Hz.

Setup: RAK5010 with Zephyr v2.3.0

Details: We have configured NRF52840 in RAK5010 to use 32kHz external crystal oscillator as a LFCLK source:

CONFIG_CLOCK_CONTROL=y
CONFIG_CLOCK_CONTROL_NRF=y
CONFIG_CLOCK_CONTROL_NRF_K32SRC_XTAL=y

This config is working and we can confirm (with scope) that 32kHz oscillator is working. We also use this clock as source for RTC. But after few hours we can see that this clock is constantly going ahead. Deviation is about +30 seconds per 24 hours. This is too much. Even using RC as clock source is more precise.

We have tried multiple RAK5010 boards, but with very same results.

Could you please provide datasheet of crystal oscillator and load capacitors used in RAK5010?

2

Welcome to RAK forum @StanP ,

I have to check to our hardware team the datasheet of the crystal and loading caps. It is still Lunar New Year holiday so we might get the information after new year. I will also share to them your observation.

3

Hi @StanP ,

This is the datasheet of the Crystal.

crystal.pdf (428.5 KB)

4

Thank you @carlrowan! Could you please give us the capacitance of the used loading capacitors?