An USB isolator helps do away with ground loops and lessens electromagnetic interference (EMI) in between the pc and also the linked device.1x GND 3V3 (P2 with two pins 2.54mm) connector may be used to power externally the WCH CH569 MCU (it is suggested to eliminate the P4/SHUNT in that situation It's not necessarily mandatory since the 3V3 LDO IC1