FT8U2XXAM
High Speed USB Controllers for serial and FIFO applications
Future Technology Devices Intl. AN232-08 Rev 1.00 Page
1
Bus Powered / Self Powered Interface Circuits
This document gives a few examples of ways to connect the FT8U232 or FT8U245 chip
for different power and reset schemes.
BUS POWERED OPTIONS
1 . The standard bus powered schematic
In this circuit, the reset is driven by a transistor which is biased so that the device is held in
reset until VCC > 3.6 volts. This ensures a reliable reset. A 10nF capacitor provides an
additional RC time delay of around 2ms.
This circuit will work for both 6 or 48 MHz operation.
Important points to note about the standard configuration –
A. The reset time is under 10mS so no special care is needed regarding USB trying to
enumerate the device whilst it is still in reset ( see below )
B. The component values are chosen such that RESET# will go inactive before RCCLK (
see below )
0.01uF
100K
2N3906
RESET#
vcc
GND
100K
470K
0.1uF
100K
RCCLK
1.5K
USBDP (D+)
3v3OUT
Connections for RESET#, RCCLK and USBDP in bus powered mode
