nRF Connect on custom nRF52840 board without ANT and VSS_PA will not boot (nRF Connect 2.0.0)

[yutingh]

Hello!

I'm running into an issue where zephyr initialization fails on a custom nRF52840 board. The nRF Desktop application fails to startup. When debugging the nrf sample CAF and App event manager, both consistently get stuck at when performing z_nrf_clock_control_lf_on(mode) (nrf_rtc_timer.c, line 639). However, the same custom board will start up with the nrF5 SDK (15.3.0). 

I was able to get both CAF, App event, and a custom nRF5 SDK project running on another custom board with a very similar layout. However, the only difference is the ANT and VSS_PA are not connected on the non-working board. The XC1 and XC2 clock are wired the same, and there is no clock wired to the XL1 and XL2.

My questions:

1. Does nRF Connect require ANT and VSS_PA to be wired up? 
2. Is there another issue that could be causing the custom nRF board to fail at initialization lfclock?

Any help would be appreciated, thanks!

[Kazi Afroza Sultana]

Hello,

1. What will happen to a custom board if nRF Connect is used, ANT and VSS_PA is not wired up, but the bluetooth module is enabled? Could this cause the silicon to be damaged?

ANT and VSS_PA pins are recommended to be grounded though capacitor according to our reference design for optimal RF performance. It also discards the harmonics. We recommend to follow exact copy of our reference layout: An exact copy of our reference layout means that both the component values and the distances and the geometries between the components should be copied.

2. Are there specific configurations in nRF Connect to ensure the internal RC oscillator starts up instead of the LF clock? The instructions are for nRF5 SDK, which is working on my custom board.

You can use the Kconfig to use the RC source for LFCLK. https://developer.nordicsemi.com/nRF_Connect_SDK/doc/2.0.0/kconfig/index.html#CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC 

Thanks.

Best Regards,

Kazi Afroza Sultana