FT2232D datasheet(28/56 Pages) FTDI

28 / 56 page

DS2232D Version 0.91

FT2232D Dual USB UART / FIFO I.C.

Figure 13 is a FT2232D design example which effectively combines the circuits shown in Figures 13 and 14 to give a

USB bus powered design with power switching and 3.3V logic drive level on both channels. Once again a P-Channel

Power MOSFET and soft start circuit are used to control the power to external logic devices. A 3.3V LDO regulator

which is supplied by the USB bus is used to provide the 3.3V supply for the VCCIO pins, as well as the external logic.

If the SI/WU pins are not being used they should be pulled up to 3.3V.

Alternatively, a dedicated power switch I.C. with inbuilt “soft-start” can be used instead of a MOSFET. A suitable

power switch I.C. for such an application would be a Micrel (

www.micrel.com) MIC2025-2BM or equivalent.

Please note the following points in connection with power controlled designs –

a) The logic to be controlled must have its own reset circuitry so that it will automatically reset itself when power is re-

The logic to be controlled must have its own reset circuitry so that it will automatically reset itself when power is re-

applied on coming out of suspend.

b) Set the Pull-down on Suspend option in the FT2232D’s EEPROM.

Set the Pull-down on Suspend option in the FT2232D’s EEPROM.

c) For USB high-power bus powered device (one that consumes greater than 100 mA, and up to 500 mA of current

from the USB bus), the power consumption of the device should be set in the max power field in the EEPROM.

A high-power bus powered device must use this descriptor in the EEPROM to inform the system of its power

requirements.

d) For 3.3V power controlled circuits the VCCIO pins must not be powered down with the external circuitry. Either

For 3.3V power controlled circuits the VCCIO pins must not be powered down with the external circuitry. Either

connect the power switch between the output of the 3.3V regulator and the external 3.3V logic, or if appropriate

power the VCCIO pin from the 3V3OUT pin of the FT2232D.

Figure 13 - Bus Powered Circuit with Power Control and 3.3V Logic Drive / IO Supply

Voltage

USB "B"

Connector

Ferrite

Bead

470R

0.1uF

VCC5V

27R

USB DM

FT2232

USB DP

33nF

3V3OUT

10nF

PWREN#

0.1uF

Switched 3.3V Power

to External Logic

P-Channel Power

MOSFET

0.1uF

Soft Start

Circuit

RSTOUT#

1.5K

RESET#

VCC5V

Decoupling Capacitors

10uF

VCC5V

0.1uF

3.3V LDO

Regulator

OUT

GND

0.1uF

SI/WUB

SI/WUA

VCC3V3

FT2232D

FT2232D Datasheet(PDF) 28 Page - Future Technology Devices International Ltd.

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