FT51A Advanced MCU with 8051 Compatible Core IC Datasheet
Version 1.5
Document No.: FT_000877
Clearance No.: FTDI#420
5 USB Power Configurations
The following sections illustrate a possible USB power configuration for the FT51A. The illustrations have
omitted pin numbers for ease of understanding since the pins differ between the various package options.
5.1 USB Bus Powered Configuration
VCC
Ferrite
Bead
1
VCC5V
27R
2
USBDM
3
4
27R
USBDP
47pF
47pF
FT51A
5
SHIELD
10nF
GND
VCC
VCC3V3
GND
100nF
+
4.7uF
100nF
GND
GND
Figure 5-1 Bus Powered Configuration
Figure 5-1 illustrates the FT51A 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 powered devices are as follows –
i)
On plug-in to USB, the device should draw no more current than 50mA.
In USB Suspend mode the device should draw no more than 500uA.
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.
ii)
iii)
iv)
The power descriptors in the internal MTP memory of the FT51A should be programmed to match the
current drawn by the device.
A ferrite bead is connectedin series with the USB power supply to reduce EMI noise from the FT51A and
associated circuitry being radiated down the USB cable to the USB host. The value of the Ferrite Bead
depends on the total current drawnby the application. A suitable range of Ferrite Beads is available from
Laird Technologies (http://www.lairdtech.com) for example Laird Technologies Part # MI0805K601R-10.
Copyright © Future Technology Devices International Limited
26
FTDI [ FUTURE TECHNOLOGY DEVICES INTERNATIONAL LTD. ]
