I was actually worried about the communication standards, and not about the voltage tolerence!
I think you are talking about the kind of device found on the following link, right?
http://www.ftdichip.com/Products/ICs/FT232BM.htm
It is actually a USB to RS232 converter. USB is one communication standard and RS232 is another one. RS232 is the standard that we use in serial port (DB9 connector) of computers. Whenever we try to interface such a serial port with mcu, we use max232, don’t we?
max232 converts RS232 serial data standard to ttl serial data standard.
I hope it is clear now!
And that is the knowledge I have, if I’m wrong readers please share your thoughts.