nRF52840 PDK debugging with 1.8V periphery

[Reto]

Hi,

I have a nRF52840 Preview Development Kit. I studied your manual, but I didn't quite understand if this is possible or not?

• I would like to debug (therefore I need the interface MCU). So far so good.
• My periphery of the nRF52 is 1.8V (does not work with >1.9V, I2C on P0.26 and P0.27)
• Is there a way that I can debug (USB plugged in in J2 connector for debugging and as power supply for the interface MCU) and I have the nRF (Vdd) supplied with an external 1.8V supply e.g. on P21?
• Which SW has to be set in which position?

Thank you for any help! Reto

[Sigurd]

Hi,

Yes, this is possible. You will need to put the VEXT->nRF switch in the ON position.

In this position you can power the nRF52840 SoC directly from the external supply connector (P21) without powering the rest of the board from the same source. I.e. the interface MCU will be powered from the J2 USB connector, while the nRF52840 is powered from the P21 connector.

See this infocenter page for more information.

[Reto]

Thank you Sigurd. It works very well. By the way, I do work with Eclipse. Fantastic tutorial you have here. You all do a great job at Nordic Semiconductor!

Reto

[Reto]

Even though debugging works fine. I still have a problem:

VDD=3.0V I2C-pull-up-resistors (R52, R53) for SCL and SCK are pulled up to VDD=3.0V.

This would destroy my sensor which runs only on 1.8V. How can I set VDD to 1.8V (Vext)?

Thank you very much! Reto

[Sigurd]

The VDD_nRF pins should have the same voltage as VEXT(when VEXT->nRF switch is in the ON position). Depending on how much current you sensor need, you could also configure a GPIO to output-mode (and high drive), and supply the sensor from the GPIO pin.

[Reto]

Thank you Sigurd. It all works very well now.