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. Does nRF Connect require ANT and VSS_PA to be wired up? 

The ANT and VSS_PA pins need to be set ( grounded through capacitor) as in the reference circuitry (https://infocenter.nordicsemi.com/topic/ps_nrf52840/ref_circuitry.html?cp=4_0_0_6_2) for the antenna to work correctly. 

...

2. Is there another issue that could be causing the custom nRF board to fail at initialization lfclock?

Since there is no wire mounted on XL1 and XL2 pin, you need to configure the application to use the internal 32.768 KHZ RC oscillator instead for the LF clock to start up.

In the nRF5 SDK you need to set the following defines to these values in the sdk_config.h file:

#define NRF_SDH_CLOCK_LF_SRC 0

#define NRF_SDH_CLOCK_LF_RC_CTIV 16

#define NRF_SDH_CLOCK_LF_RC_TEMP_CTIV 2

#define NRF_SDH_CLOCK_LF_ACCURACY 1

However it is recommended that you follow the reference circuitry to ensure normal/optimal antenna performance, so please follow the reference and do a new revision of your custom board. 

Thanks.

Best Regards,

Kazi Afroza Sultana

[yutingh]

Hi, 

Thanks for the response. A few follow up questions.

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?

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.

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