FT232BM datasheet(21/54 Pages) FTDI

21 / 54 page

DS2232C Version 1.2

Page 21 of 54

FT2232C Dual USB UART / FIFO I.C.

8.3 USB Bus Powered and Self Powered Configuration

Figure 8 - USB Bus Powered Configuration

Figure 8 illustrates the FT2232C in a typical USB bus powered configuration. A USB Bus Powered device gets its

power from the USB bus. Basic rules for USB Bus power devices are as follows –

a) On plug-in, the device must draw no more than 100mA

b) On USB Suspend the device must draw no more than 500μA.

c) A High Power USB Bus Powered Device (one that draws more than 100mA) should use the PWREN# pin to keep

the current below 100mA on plug-in and 500μA on USB suspend.

d) A device that consumes more than 100mA can not be plugged into a USB Bus Powered Hub

e) No device can draw more that 500mA from the USB Bus.

The power descriptor in the EEPROM should be programmed to match the current draw required by the device.

A Ferrite Bead is connected in series with USB power to prevent noise from the device and associated circuitry (EMI)

being radiated down the USB cable to the Host. The value of the Ferrite Bead depends on the total current required

by the circuit – a suitable range of Ferrite Beads is available from Steward (

www.steward.com) for example Steward

Part # MI0805K400R-00 also available from

DigiKey, Part # 240-1035-1.

0.1uF

VCC

27R

USB "B"

Connector

27R

USB DM

RSTOUT#

FT2232C

USB DP

Ferrite Bead

1.5K

33nF

3v3OUT

470R

18 25 34

10nF

VCC

RESET#

Decoupling Capacitors

10uF

VCC

0.1uF

TEST

EECS

EESK

EEDATA

10K

6MHz

27pF

XTIN

44 XTOUT

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