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nrf52840(DK) External Voltage, VDD and VLogic

Gmrck

Dear Nordic team,

I have a complex question. In my project I use components which operate at 2.25V as well as they expect 2.25V logic levels.

My idea is to use nrf52840 chip and run it natively with 2.25V, so the logic level of the chip is also 2.25V, which will let me get rid of the logic level shifters components.

I was able to connect the PPK2 in source mode to the External power supply of my nrf52840DK, supply 2.25V via the power profiler application and see, that the code executing on the nrf52840DK indeed sends out 2.25V as a logic HIGH to the GPIOS. However, as soon as I've connected the nrf52840DK to the computer with the USB cable, the logic level changed to 3.3V. I assume the USB took over. Therefore, my first question:
- Is it possible to supply nrf52840DK with the external power and stick to that external voltage as the logic level, but at the same time still being able to utilise USB for debugging purposes in nrf Connect SDK. I've read there's a way to write to registers, but I am wondering if there's a hardware way to do this, without any programming of the chip.

The next question is related to the stage of programming the final device with the nrf52840 chip on it. If I am able to run the whole system with 2.25V and the same logic level, once I decide to program my external nrf52840 chip via SWD using nrf52840DK as a programming board, will the DK be able to do it with 2.25V logic? Or will it switch to 3.3V and then the whole custom device will maintain the 3.3V while the programmer runs? This is critical, since 3.3V will damage the other components in the project which need no more than 2.25V to  operate.

  • 0 in reply to Asbjørn

    Hi, Asbjorn.

    Sorry for the confusion. The components accept 2.25V-2.5V, this is where I've confused you by accident. So, 2.4V on nrf52840DK should work fine for the application and the rest of the components.

    While developing, I've configured 52840DK in High Voltage mode and have changed the REGOUT0 for 2.4V. This works as expected, with J3 USB delivering the high voltage (SW9 in USB position) and J2 USB delivering the debug/console capabilities. Still curious whether it is possible to have just J2 or J3 USB for both High Voltage and debugging, to not have 2 USB ports occupied at the same moment.

    When I switch to the final setup with the external voltage, I won't need the High Voltage mode and will just supply the external voltage of 2.4V, so the nrf52840 chip picks it up as VDD and VLogic.

    However, do I read correctly, that if I use nrf52840DK as a programmer board to program my external nrf52840 SOC, the SWD will deliver 3.3V as the VDD and VLogic to that chip? And there's no possibilities for SWD programmeron the DK to be in that nrf52840DK High Voltage mode with the VDD/VLogic being 2.4V? Otherwise I will need either a level shifter as you suggested or I will need to program the chip separately, before "inserting" it in the final board.

  • 0 in reply to Gmrck
    Gmrck said:
    However, do I read correctly, that if I use nrf52840DK as a programmer board to program my external nrf52840 SOC, the SWD will deliver 3.3V as the VDD and VLogic to that chip? And there's no possibilities for SWD programmeron the DK to be in that nrf52840DK High Voltage mode with the VDD/VLogic being 2.4V? Otherwise I will need either a level shifter as you suggested or I will need to program the chip separately, before "inserting" it in the final board.

    This is correct, it's a limitation on the DK for some, but for a majority of customers developing it is fine. Some require other voltages and then external debugger with level shifters are required. It's a trade off for us with regard to functionality and cost of the DK. We do have level shifters on the nRF54L15 DK: https://docs.nordicsemi.com/bundle/ug_nrf54l15_dk/page/UG/nRF54L15_DK/program_debug/debug_out_ext_board.html

    So you could get one of those to program your nRF52840 board at 2.25V.

    Best regards

    Asbjørn

  • 0 in reply to Asbjørn

    Hi, Asbjorn,

    Thanks for your suggestion on nrf54 DK. And thanks for making all your Dev Boards and Kits (like PPK) affordable to everybody.

  • 0 in reply to Asbjørn

    Asbjorn, still on the NOTE from the 52840DK documentation:

    https://docs.nordicsemi.com/bundle/ug_nrf52840_dk/page/UG/dk/hw_debug_out.html


    Note: The voltage supported by external debugging/programming is VDD voltage. Normally, this is 3 V when running from USB. But if the onboard nRF52840 SoC is supplied from either USB or lithium-ion (Li-ion) and the nRF power source switch (SW9) is in either Li-Po or USB position, then the VDD can be set by the nRF52840 firmware. Make sure the voltage level of the external board matches the VDD of the nRF52840 DK.


    I read it like the following:
    If I run nrf52840DK in the HIGH VOLTAGE mode, then the SWD voltage will follow my VDD voltage. Which means, if I run in HV Mode and set my REGOUT0 to 2.4V, my VDD is 2.4V and hence my SWD Voltage from nrf52840DK is also 2.4V. 

    Am I reading it incorrectly? Because if this is correct, I am pretty much good with my set up. I can always run my DK in High Voltage mode with VDD 2.4V anytime I need to program an external board which is the part of the 2.4V-tolerant circuit.

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