FT245R USB UART I.C. Datasheet Version 1.05

© Future Technology Devices International Ltd. 2005

Page 19

7. Device Configurations

Please note that pin numbers on the FT245R chip in this section have deliberately been left out as they vary between

the FT245RL and FT245RQ versions of the device. All of these configurations apply to both package options for the

FT245R device. Please refer to Section 4 for the package option pin-out and signal descriptions.

7.1 Bus Powered Configuration

Figure 13 - Bus Powered Configuration

Figure 13 illustrates the FT245R in a typical USB bus powered design configuration. A USB Bus Powered device gets

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

i) On plug-in to USB, the device must draw no more than 100mA.

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

iii) A Bus Powered High Power USB 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.

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

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

The power descriptor in the internal EEPROM should be programmed to match the current draw of 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.

FT245R

A

G

N

D

G

N

D

G

N

D

G

N

D

T

E

S

T

100nF

3V3OUT

VCCIO

NC

RESET#

NC

+

100nF

10nF

Vcc

D0

D1

D2

D3

D4

D5

D6

D7

RXF#

WR#

RD#

TXE#

USBDP

USBDM

VCC

1

2

3

4

5

OSCI

OSCO

PWREN#

Ferrite

Bead

+

4.7uF

SHIELD

GND

GND

GND

GND

Vcc