Issue with Unknown Device detection on nRF5340 – Flashing works, but Debugging/Recovery fails

RE: Issue with Unknown Device detection on nRF5340 – Flashing works, but Debugging/Recovery fails

Vidar Berg — Wed, 18 Mar 2026 06:09:07 GMT

Your overlay is correct, so if it is being applied it should not be an issue with the regulator settings. If you want to confirm that it is being applied, you can check the final DT configuration in the zephyr.dts file generated for your application in the build folder. You can also try to read the regulator registers with nrfutil (if it doesn't fail to connect).

Reading VREGMAIN.DCDCEN:

nrfutil device read --address 0x50004704 --direct

RE: Issue with Unknown Device detection on nRF5340 – Flashing works, but Debugging/Recovery fails

gwan0624 — Wed, 18 Mar 2026 01:51:27 GMT

I'm using LDO mode without an inductor and updated the overlay file accordingly.

Is it possible the power instability is because the nRF5340 is still stuck in DCDC mode? Since the device fails to boot, I suspect the internal regulator registers haven't actually changed to LDO mode.

RE: Issue with Unknown Device detection on nRF5340 – Flashing works, but Debugging/Recovery fails

Vidar Berg — Tue, 17 Mar 2026 13:20:46 GMT

Does your design include the optional DCDC inductors? If you build the FW for the nRF5340 DK, the DCDC regulators will be enabled by default, and if the inductors are not included, the regulator will fail to provide a stable supply voltage internally in the chip which commonly leads to issues such as being unable to re-program the chip.

Best regards,

Vidar

RE: Issue with Unknown Device detection on nRF5340 – Flashing works, but Debugging/Recovery fails

gwan0624 — Tue, 17 Mar 2026 08:11:58 GMT

Thank you for your response.

Unfortunately, the recovery was unsuccessful even after following the procedure. Given the unstable outputs on the VDD and RESET pins, it appears the MCU itself has been damaged.

Issue with failing VDD output – Is recovery possible? (nRF5340)

I will need to reorder the PCB and proceed with further testing

Best regards,
gwan0624

RE: Issue with Unknown Device detection on nRF5340 – Flashing works, but Debugging/Recovery fails

Vidar Berg — Tue, 10 Mar 2026 15:51:38 GMT

Hello,

Yes, as you say, nrfutil will not be able to correctly identify the chip when approtect is enabled. To unlock approtect on the nRF5340, you must perform the recovery procedure on the network core before you recover the application core. Please try this and see if the problem persists.

nrfutil device recover --core network
nrfutil device recover

Best regards,

Vidar