The nRF5340 DK has a power source switch (SW9) for selecting between VDD (default), Li-Po, and USB power supplies for the nRF5340 SoC.
The nRF5340 SoC has a high voltage buck regulator that can support up to 5 V input. In the VDD position, the SoC is powered from the onboard buck regulator, coin cell battery, or external supply (P21). In the Li-Po position, the high voltage regulator of the SoC is supplied directly from the Lithium-polymer (Li-Poly) battery connectors (J6 or P27). In the USB position, the Universal Serial Bus (USB) high voltage regulator is powered by thenRF5340 USB connector (J3).
When the high voltage regulator is used, the VDD_nRF voltage can be set by SoC firmware. To make sure the rest of the Development Kit (DK) has the same voltage level, the VDD of the DK is sourced by a regulator following the VDD_nRF voltage when the high voltage regulator is used.
To make sure that the nRF5340 SoC is not powered when the nRF power switch (SW8) is OFF, two load switches are used, one for the high voltage regulator (U15) and one for the USB supply (U20). These switches are controlled by VDD.