Are you trying to run this system with the Nano plugged into the computer's USB and the main supply being fed by something else?
As you have a CH340 you have not got a real Nano and it looks like the clone makers have screwed up on the design if this is getting hot. In this case then don't power the board externally at all and just use the USB power. Note you will need to switch in external power if you want to run it without the USB connected.