DLP Design USB-Parallel FIFO Module DLP-USB245R User Manual page 9

Figure 2.
Figure 2 illustrates a typical USB self-powered configuration. A USB self-powered device gets
its power from its own power supply and does not draw current from the USB bus. Basic rules
for USB self-powered devices are as follows:
1. A self-powered device should not force current down the USB bus when the USB host or hub
controller is powered down.
2. A self-powered device can take as much current as it likes during normal operation and
during USB Suspend as it has its own power supply.
3. A self-powered device can be used with any USB host and both bus- and self-powered USB
hubs.
Figure 3.
Figure 3 shows how to configure the DLP-USB245R to interface with a 3.3V logic device. In this
example, the target electronics provide the 3.3 volts via the VCCIO line (Pin 7) which, in turn,
will cause the FT245R interface I/O pins to drive out at the 3.3V level.
Rev. 1.0 (November 2008)
5.0V
7
8
9
Self-Powered
5V System
8 Data Lines
RXF#
3.3V
RD#
7
8
TXE#
9
WR
Bus-Powered
5V System with
3.3V Logic Interface
3.3V
Microcontroller
9 © DLP Design, Inc.