PPK II Source Mode + nRF52 DK v3.0.0

[ct0]

I am trying to measure current on a nRF52 DK v3.0.0 using PPK II in source mode.

I cut SB9 and soldered SB12 as described in this guide: https://docs.nordicsemi.com/bundle/ug_nrf52832_dk/page/UG/dk/prepare_board.html

The problem is my firmware won't boot unless the DK is connected via USB.

What I am concerned about is the guide above explicitly says:

Note: While SB12 is shorted, the DK must not be powered from the USB if there is an external supply connected because the protection diode has been bypassed.

So is powering from PPK considered to be external power or not?

The PPK guide includes a diagram where the DK is connected via USB:

https://docs.nordicsemi.com/bundle/ug_ppk2/page/UG/ppk/measure_current_source_meter.html

But its for nrf9160 DK. Will it be the same for nRF52 DK?

Also the nrf52 guide says:

It is not recommended to use a USB connector to power the Development Kit (DK) during current measurements due to potential noise from the USB power supply. It is recommended to power the DK from a coin cell battery or external power supply on connector P21 (1.7 V to 3.6 V).

Which adds confusion. Is it even possible to measure without powering the DK, and just powering the chip via PPK in source mode? If not, what's the correct way to do the measurements?

[SwRa]

Hello,

So is powering from PPK considered to be external power or not?

The PPK2 acting as a source meter is effectively an external supply connected to P22 (VDD_nRF). But that should not be an issue in your case. Soldering SB12 is optional. You can power the DK using USB and carry out power measurements. The USB powers the interface MCU (needed for your firmware to boot/debug), while the PPK2 via P22 powers only the SoC. This is safe because P22 and the USB/P21 supply rail are on separate domains after cutting SB9.

Best Regards,

Swathy

[ct0]

Thanks for the reply.

So powering the chip alone is not enough then, and the DK must always be powered as well.

That makes sense, but I think the documentation could use some clarification regarding that.