Datasheet
Copyright © 2010 Future Technology Devices International Limited 22
Document No.: FT_000052
FT245R USB FIFO IC Datasheet Version 2.12
Clearance No.: FTDI# 39
7 USB Power Configurations
The following sections illustrate possible USB power configurations for the FT245R. The illustrations have
omitted pin numbers for ease of understanding since the pins differ between the FT245RL and FT245RQ
package options.
All USB power configurations illustrated apply to both package options for the FT245R device. Please refer
to Section 3 for the package option pin-out and signal descriptions.
7.1 USB Bus Powered Configuration
FT245R
GND
GND
100nF
VCC
USBDM
USBDP
VCCIO
NC
RESET#
NC
OSCI
OSCO
3V3OUT
A
G
N
D
G
N
D
G
N
D
G
N
D
T
E
S
T
Vcc
1
2
3
4
GND
SHIELD
GND
VCC
100nF
4.7uF +
5
10nF
Ferrite
Bead
D0
D1
D2
D3
D4
D5
D6
D7
RXF#
TXE#
RD#
WR
PWREN#
Vcc
10K
Figure 7.1 Bus Powered Configuration
Figure 7.1 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 should draw no more current than 100mA.
ii) In USB Suspend mode the device should draw no more than 2.5mA.
iii) A bus powered high power USB device (one that draws more than 100mA) should use the
PWREN# to keep the current below 100mA on plug-in and 2.5mA on USB suspend.
iv) A device that consumes more than 100mA cannot be plugged into a USB bus powered hub.
v) No device can draw more than 500mA from the USB bus.
The power descriptors in the internal EEPROM of the FT245R should be programmed to match the current
drawn by the device.
A ferrite bead is connected in series with the USB power supply to reduce EMI noise from the FT245R and
associated circuitry being radiated down the USB cable to the USB host. The value of the Ferrite Bead
depends on the total current drawn by the application. A suitable range of Ferrite Beads is available from
Steward (www.steward.com), for example Steward Part # MI0805K400R-10.
Note: If using PWREN#, the pin should be pulled to VCCIO using a 10kΩ resistor.