Zephyr: VBUS Detection

BME554L - Fall 2025

Dr. Mark Palmeri, M.D., Ph.D.

Duke University

August 25, 2025

What is VBUS?

nRF52833 Product Specification

VBUS Detection

Why is this important?

  • Safety! Shock risk
  • USB charging / power provides a physical connection to a power source.
  • IEC60601 has very different safety testing requirements for “wall” powered vs. battery-powered devices.

Firmware Implementation

#include <nrfx_power.h> // NOTE: This is not a Zephyr library!!  It is a Nordic NRFX library.

bool usbregstatus = nrf_power_usbregstatus_vbusdet_get(NRF_POWER);
if (usbregstatus) {
    // VBUS detected
} else {
    // VBUS not detected
}
  • If you have a battery-powered device that cannot be used while charging, could change to “charging” state that would block operation.

Drawbacks

  • Not ideal; this is now chip-specific code.
  • This breaks the Zephyr abstraction layer; now firmware code is hardware-specific. :(
  • But… Zephyr usbc_vbus API is not implemented for the nRF52833.

How to Test

You can use the second USB port (nRF USB) on the nRF52833 DK to test this. The second USB port is connected directly to the VBUS pin on the nRF52833.

Resources