Programming external MCU with nRF5340 DK

RE: Programming external MCU with nRF5340 DK

Joao Colombari — Mon, 22 Jun 2026 19:49:56 GMT

Hi guys,

I have a few custom PCBs based on the nRF5340 and several peripheral ICs. One of these ICs has an absolute maximum supply voltage of 1.98 V. The boards do not include any external over-voltage protection.

For debugging, I have been using an nRF5340 DK as a J-Link probe, following the setup described here, with SB19 shorted so that the probe senses the target VDD level.

Several boards eventually developed a hard short between VDD and GND. After some investigation, I found that the failed component was the IC with the 1.98 V maximum supply rating. Once it was removed, SWD access to the nRF5340 was restored.

My question is: when using the DK as a debugger in this configuration, is there any possibility that the probe could briefly drive or expose the target to a higher voltage (e.g., 3.3 V) before it detects and adapts to the target VDD level?

I am trying to determine whether such a transient could explain the failures I observed.

Best regards,

João Colombari

RE: Programming external MCU with nRF5340 DK

boxerwitness — Wed, 20 Nov 2024 02:29:10 GMT

Yes, you can short SB19 on the nRF5340 DK to allow your external board's VDD (e.g., 1.8V) to supply VIO_REF for debugging, as long as the external board provides a stable VDD within the supported range (1.8V to 3.6V). This setup eliminates the need for level shifters for programming and debugging.

solar smash

RE: Programming external MCU with nRF5340 DK

Charlie — Mon, 14 Oct 2024 10:26:08 GMT

Hi,

The programming and debugging should work as long as the GPIO voltage is matched between JLink-OB chip and your target chip.

You can test and monitor with a multimeter when you are programing.

regards,

Charlie

RE: Programming external MCU with nRF5340 DK

mm784 — Wed, 09 Oct 2024 17:36:33 GMT

Hi Charlie,

Thank you for confirming.

I have 2 boards, one is battery powered, and the other one is USB powered. Can you also confirm the following.

1. On the board which is battery powered, the VDD_nRF can fluctuate depending on battery state, from 3V to 2.5V and lower. The information you shared indicates that for debugging this board, the SB 19 must be shorted so that the reference voltage of the debugger on the DK is always the same as the VDD of the SoC on my external board.

2. On the board that is USB powered, VDDH is 5V. The default output of the internal high voltage regulator VREGH is 1.8V. Does it mean that even for programming this external SoC that is powered by 5V on VDDH, the SB19 must still be shorted, because by default the VDD_nRF and its I/O voltage level will be 1.8V.

Thank you

RE: Programming external MCU with nRF5340 DK

Charlie — Wed, 09 Oct 2024 13:45:52 GMT

Hi,

Yes, you can, but make sure you nRF5340DK has same debug output circuit design as following.

RE: I can't program external board with nRF5340 2.0.2

You can find your nRF5340DK schematic here: www.nordicsemi.com/.../Download

Best regards,

Charlie