FT240X USB 8-BIT FIFO IC Datasheet
Version 1.3
Document No.: FT_000626 Clearance No.: FTDI# 259
6 USB Power Configurations
The following sections illustrate possible USB power configurations for the FT240X. The illustrations have
omitted pin numbers for ease of understanding since the pins differ between the FT240XS and FT240XQ
package options.
All USB power configurations illustrated apply to both package options for the FT240X device. Please refer
to Section 0 for the package option pin-out and signal descriptions.
6.1 USB Bus Powered Configuration
VCC
Ferrite
Bead
1
VCC
27R
2
USBDM
27R
3
4
USBDP
47pF
FT240X
5
47pF
RESET#
VCCIO
SHIELD
10nF
GND
3V3OUT
D
N
D
GND
N
G
A
G
VCC
100nF
+
4.7uF
100nF
GND
GND
Figure 6.1 Bus Powered Configuration
Figure 6.1 illustrates the FT240X 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)
ii)
iii)
On plug-in to USB, the device should draw no more current than 100mA.
In USB Suspend mode the device should draw no more than 2.5mA.
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.
A device that consumes more than 100mA cannot be plugged into a USB bus powered hub.
No device can draw more than 500mA from the USB bus.
iv)
v)
The power descriptors in the internal MTP memory of the FT240X 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 FT240X 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 # MI0805K601R-10.
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