The nRF5340 DK supports programming and debugging external boards with nRF51 Series , nRF52 Series, or nRF53 Series System on Chip (SoC)s. To debug an external board with SEGGER J-Link OB IF, connect to the Debug out connector (P19) with a 10-pin cable.
Figure 1. Debug output connector
When the external board is powered, the interface MCU detects the supply voltage of the board and program/debug the target chip on the external board instead of the onboard nRF5340 SoC.
Note: The voltage supported by external debugging/programming is VDD voltage. Normally, this is 3 V when running from USB. But if the onboard nRF5340 SoC is supplied from either USB or lithium-ion (Li-ion) and the nRF power source switch (SW9) is in either Li-Po or USB position, then the VDD can be set by the nRF5340 firmware. Make sure the voltage level of the external board matches the VDD of the nRF5340 DK.
You can also use P20 as a debug out connection to program shield-mounted targets. For both P19 and P20, the interface MCU detects the supply voltage on the mounted shield and programs or debugs the target.If the interface MCU detects target power on both P19 and P20, it programs or debugs the target connected to P19 by default.
If it is inconvenient to have a separate power supply on the external board, the nRF5340 DK can supply power through the Debug out connector (P19). To enable this, short solder bridge SB47. While SB47 is shorted, it is not possible to program the onboard nRF5340 SoC even if the external board is unplugged.