Mixing a bus and self powered design is not recommended. VCCIO should be connected to either 5V or 3.3V in one of the following configurations:
| • | Entirely bus powered, that is from the USB port (VCC and VCCIO pins). In the case where 3.3V IO's are required a local 3.3V regulator is needed which can be supplied from the USB bus. Alternatively, in some cases, where only a small amount of current is required (< 5mA), it may be possible to use the in-built regulator of the FTDI device (where available) to supply the 3.3V to VCCIO without any other components being required. In this case, connect VCCIO to the 3V3OUT pin of the FTDI device. |
| • | Entirely self powered, that is from the local supply on your board. In the case where 3.3V IO's are required, you will need 5V and 3.3V to be available on your board. |