You can power the System on Chip (SoC) directly from a source without powering the rest of the Development Kit (DK) from the same source.
The external source can be connected to the external supply connector (P21) and the VEXT→nRF switch (SW10) put in the ON position. The nRF power source switch (SW9) must be in the VDD position, and the allowed voltage range is 1.7–3.6 V.
Since only the nRF52840 SoC is supplied from the source, it is recommended to supply the VDD domain from a different source to prevent the SoC from being connected to a device without power.
To avoid voltage differences on the DK, the External supply is also connected to the input of the voltage follower when SW10 is in the ON position. The voltage follower circuit requires 5 V to be present on the DK. See 5 V power sources for more information.
The voltage follower can be disconnected from the External supply by cutting SB58. To prevent leakage due to voltage differences, the DK should be set to the nRF only mode. See Operating modes for more information.