FT232BQ USB UART ( USB - Serial) I.C.
Figure 15
Self Powered Circuit with 3.3V logic drive / supply voltage
VCC3V
VCC5V
470R
USB "B"
Connector
1
27R
0.1uF
3
26
13
30
2
3
4
V
C
C
V
C
C
V
C
C
I
A
V
C
C
27R
6
O
3v3OUT
33nF
FT232BM
FT232BQ
4K7
8
7
USB DM
USB DP
VCC3V
10K
1K5
14
PWRCTL
5
4
RSTOUT#
RESET#
VCC5V
A
G
N
D
G
N
D
G
N
D
+
9
17
29
0.1uF
0.1uF
10uF
Decoupling Capacitors
Figure 15 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 FT232BQ to supply the 3.3V without any other components being
required. In this case, connect VCCIO to the 3v3OUT pin of the FT232BQ.
Note that in this case PWRCTL is pulled up to VCCIO, not VCC.
DS232BQ Version 1.8
© Future Technology Devices Intl. Ltd. 2005
Page 23 of 25
FTDI [ FUTURE TECHNOLOGY DEVICES INTERNATIONAL LTD. ]
