nRF5340 with internal load caps for 32M XTAL

Hello,

The target MCU on nRF5340 DK seems to use internal load caps for the high frequency 32MHz XTAL because the board does not have external load caps. 

The nRF5340 specification sheet mentions that the internal caps must be configured before enabling them. 

Does it mean that every sample application configures this on the nRF5340?

When I load the "blinky" example, I see the following in the Output .config

1. In what config file is this configured and what are the default values?

2. What is the default startup clock of the SoC? Since the internal caps for the crystal must be configured first, I imagine the SoC must use another clock source before the external XTAL is enabled. 

  • Hi Einar,

    Coincidentally, even though this configuration worked for advertising (with the synthesized LFCLK), I started experiencing disconnections when I ran another sample code for establishing a connection to the phone through the nRF Connect app. 

    "Reason 8" being Connection Timeout, I started investigating connection timing parameters and in my searches I stumbled upon this ticket. 

     nRF5340 Peripheral BLE connections always fail with reason 0x3e (62) 

    In here, it was mentioned that the RC oscillator configurations should be done on BOTH the App and Network cores. After doing so, I was able to start the radio using RC oscillators, and to establish a stable BLE connection without disconnections.

    So in summary, I am no longer using HFXO to generate LFCLK. I enabled RC oscillators in both application MCU and network MCU (hci_ipc) in their respective prj.conf files.  

    #Internal 32kHz RC Oscillator
    CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=y
    CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC_CALIBRATION=y
    CONFIG_CLOCK_CONTROL_NRF_K32SRC_500PPM=y
    Question: Is there any explicit documentation from Nordic which mentions that this configuration must be enabled in both app/network if an external 32kHz XTAL is not used? I could not find any. 
    Mikael
  • Hi,

    I am glad to see you found the issue. This is a good point, I do not believe it is documented anywhere that you must configure the clock source on both the application and network core (and if you have several images like a bootloaders they also need the same clock configuration). I will forward this internally.

    PS: As this is needed on all applications it makes sense to add it to your board files.

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