Unable to use LDO power on NRF52840

[harryle]

Hello,

I want to use only LDO (not DC/DC) regulation on my nRF52840 design. The documentation states that LDO is the default for both REG0 and REG1, and that DC/DC should only be enabled if the external LC filter is present. Based on this, I removed the LC filter from my hardware.

However, after removing the LC filter, behavior is unstable:

• Sometimes the chip fails to program,
• Sometimes it programs but does not run.

My questions:

1. What is the correct way to ensure the nRF52840 always uses LDO mode for both REG0 and REG1, both in hardware and firmware?
2. Are there specific devicetree or Kconfig settings required to guarantee LDO mode and prevent the firmware from enabling DC/DC by default?
3. Is it safe to remove the LC filter if LDO mode is always used, or could there be other issues?
4. What could cause programming or boot failures after removing the LC filter, even though LDO should be the default?

What I have tried:

• In the devicetree, I set:

  &reg1 { regulator-initial-mode = <NRF5X_REG_MODE_LDO>; };

Is there a checklist or best practice to ensure the nRF52840 is always in LDO mode and safe to run without the DC/DC LC filter? What else should I check if I still see programming or boot issues?

Thank you!

[Simonr]

Hi

The schematics look good. Both DCDCEN registers should be set to 0 (disabled). This should be disabled by default AFAIK, but you can set &reg0 { regulator-initial-mode = <NRF5X_REG_MODE_LDO>; }; to make sure as well. Note that if it has been run with DCDCEN0 enabled at all without the required components, it not certain that you'll be able to reflash the device.

Best regards,

Simon

[harryle]

Hi, thank you for your suggestion, I created a blank application and was able to successfully set both reg to disabled. It also worked on our PCB board.

But the firmware of the project I'm working on still failed even with the same setting as the blank one I created. Is there any chance that some component on zephyr can automatically override those config and make the chip use DCDC power instead of LDO?. I'm using UART, BLE, NFC on the project.

[harryle]

Hi Simonr,

It turns out that the MCU boot enable DCDC by default and try disabling it on the app takes no effect. I added this to also the mcuboot.overlay, not just the app overlay, and it worked:
&reg1 { regulator-initial-mode = <NRF5X_REG_MODE_LDO>; };

[Simonr]

Ah, that makes sense. I didn't realize you had MCUBoot as part of your project as well. Thank you for sharing the solution. Closing this case then. Feel free to reopen if you have any further issues.

Best regards,

Simon