Been bitten by the CH340/341 of the cinese arduino nano clones myself in these day .
Found the right one right away after a short search on the internet it' here .
After experimenting with the nano clone have to add a few caveat...
0) old CH340/341 Drivers can PANIC the Mac OS X Kernel
1) DO NOT use 3.3 Volt for anything than a few mA as it's generated by the CH340 chip so is not capable of more than few mA
2) DO NOT short o put a too strong load (say less than 500mA) on the power out(5V) pin of the arduino nano when USB powered as the diode put in series with the USB power can blow up ( it's a SCHOTTKY) .
3) TRY to let the CH340/341 alone undisturbed when connected to the Mac via USB.
That all for today. If i come up with something else will report here.