Document No.: FT_000329
FT232BL/BQ USB UART IC Datasheet Version 2.2
Clearance No.: FTDI# 171
6.3.2 Self Powered Circuit with 3.3V logic drive / supply
Figure 6.4 Self Powered Circuit with 3.3V logic drive / supply
Figure 6.4 is an example of a USB self powered design with 3.3V interface. In this case VCCIO is supplied
by an external 3.3V supply in order to make the device IO pins drive out at 3.3V logic level, thus allowing
it to be connected to a 3.3V MCU or other external logic. A USB self powered design uses its own power
supplies, and does not draw any of its power from the USB bus. In such cases, no special care need be
taken to meet the USB suspend current (0.5 mA) as the device does not get its power from the USB port.
As with bus powered 3.3V interface designs, 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 FT232B to supply the 3.3V without
any other components being required. In this case, connect VCCIO to the 3v3OUT pin of the FT232B.
Note that in this case PWRCTL is pulled up to VCCIO, not VCC.
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