I've developed a custom board with nRF5340-QKAA (see schematic sheet attached).
nRF5340's VDD pins are not tied to VDDH pin, then I assume the nRF5340 automatically starts in High Voltage mode.
In my design I use
Q2: How to increase VDD_nRF to 3.3 V ? Is there some special configuration switch in Zephyr ?