FT232R Future Technology Devices Intl Ltd., FT232R Datasheet - Page 21

• Manufacturer Part Number: FT232R
• Manufacturer: Future Technology Devices Intl Ltd.

Figure 12 - Bus Powered with 3.3V / 5V Supply and Logic Drive
Figure 12 shows a configuration where a jumper switch is used to allow the FT232R to be interfaced with a 3.3V or
5V logic devices. The VCCIO pin is either supplied with 5V from the USB bus, or with 3.3V from the 3V3OUT pin. The
supply to VCCIO is also used to supply external logic.
Please note the following in relation to bus powered designs of this type -
i)
ii) The maximum current source from USB Bus during normal operation should not exceed 100mA, otherwise a bus
Another possible configuration would be to use a discrete low dropout regulator which is supplied by the 5V on the
USB bus to supply 2.8V - 1.8V to the VCCIO pin and to the external logic. VCC would be supplied with the 5V from
the USB bus. With VCCIO connected to the output of the low dropout regulator, would in turn will cause the FT232R
I/O pins to drive out at 2.8V - 1.8V logic levels.
For USB bus powered circuits some considerations have to be taken into account when selecting the regulator –
iii) The regulator must be capable of sustaining its output voltage with an input voltage of 4.35V. A Low Drop Out
iv) The quiescent current of the regulator must be low in order to meet the USB suspend total current requirement of
An example of a regulator family that meets these requirements is the MicroChip / Telcom TC55 Series of devices
(www.microchip.com). These devices can supply up to 250mA current and have a quiescent current of under 1μA.
FT232R USB UART I.C. Datasheet Version 1.02
PWREN# or SLEEP# signals should be used to power down external logic during USB suspend mode, in order to
comply with the limit of 500μA. If this is not possible, use the configuration shown in
powered design with power switching
(L.D.O.) regulator must be selected.
<= 500μA during USB suspend.
SHIELD
5
7.4 USB Bus Powered with 3.3V / 5V Supply and Logic Drive / IO Supply Voltage
1
2
3
4
10nF
100nF
GND
+
Ferrite
Bead
4.7uF
GND
Jumper
Vcc
+
1
2
3
(Section
Vcc
7.3) should be used.
GND
100nF
VCC
USBDM
USBDP
3V3OUT
VCCIO
RESET#
OSCI
OSCO
NC
NC
G
A
N
D
© Future Technology Devices International Ltd. 2005
FT232R
G
N
D
G
N
D
GND
G
N
D
Section
T
E
S
T
CBUS0
CBUS1
CBUS2
CBUS3
CBUS4
DCD#
DSR#
RTS#
CTS#
DTR#
RXD
TXD
RI#
7.3.
3.3V or 5V Supply
to External Logic
PWREN#
SLEEP#
100nF