DS_FT2232D Datasheet, PDF (51/61 Pages) List of Unclassifed Manufacturers – Future Technology Devices International Ltd

Document No.: FT_000173
FT2232D DUAL USB TO SERIAL UART/FIFO IC Datasheet
Version 2.05
Clearance No.: FTDI# 127
Figure 8.17 Fast Opto-Isolated Serial Interface Example
In the example shown in figure 8.18 two Agilent HCPL-2430 (see the semiconductor section at
www.agilent.com) high speed opto-couplers are used to optically isolate an external device which
interfaced to USB using the FT2232D. In this example VCC5V is the supply for the FT2232D (bus or self
powered), and VCCE is the supply to the external device.
Care must be taken with the voltage used to power the photoLED‟s. It should be the same supply that
the I/Os are driving to, or the LED‟s may be permanently on. Limiting resistors should be fitted in the
lines that drive the diodes. The outputs of the opto-couplers are open-collector and so need a pullup
resistor.
Testing
Fast serial mode has been tested using an Scenix (Ubicom), SX28 microcontroller (see
www.ubicom.com) which was configured in loopback mode. This was done both with, and without HP
HCPL-2430 opto-isolators in place. The isolators add a considerable delay to the turnaround time seen by
the micro. This was close to 100 nS with the high speed HCPL-2430 device. This is the combined delay of
the clock signal from the microcontroller going through an opto-coupler to the chip, and the data from
the FT2232D chip going through the other opto-coupler back to the microcontroller.
Copyright © 2010 Future Technology Devices International Limited
51