nRF52840 System on Chip (SoC) can be powered directly from an external 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. Set the VEXT→nRF switch SW10 to the ON position and the nRF power source switch SW9 to the VDD position. The allowed voltage range is 1.7 V to 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 supplied to the DK. For more information, see 5 V power sources.
The voltage follower can be disconnected from the external supply by cutting SB58. To prevent leakage due to voltage differences, set the DK to the nRF only mode. For more information, see Modes of operation.