DS_FT231X Datasheet, PDF (23/44 Pages) List of Unclassifed Manufacturers – Future Technology Devices International Ltd FT231X

FT231X USB TO FULL HANDSHAKE UART IC
Datasheet
Version 1.2
Document No.: FT_000565 Clearance No.: FTDI# 261
6.2 Self Powered Configuration
1
2
3
4
4k7
5
SHIELD
GND
10k
VCC(3.3-5.25V)
47pF
27R
27R
47pF
GND
VCC
USBDM
USBDP
FT231X
VBUS_SENSE
VCCIO
RESET#
3V3OUT
100nF
VCC
GND
100nF
+
4.7uF
100nF
GND
GND
Figure 6.2 Self Powered Configuration
Figure 6.2 illustrates the FT231X in a typical USB self powered configuration. A USB self powered device
gets its power from its own power supply, VCC, and does not draw current from the USB bus. The basic
rules for USB self powered devices are as follows –
i)
A self powered device should not force current down the USB bus when the USB host or hub
controller is powered down.
ii)
A self powered device can use as much current as it needs during normal operation and USB
suspend as it has its own power supply.
iii)
A self powered device can be used with any USB host, a bus powered USB hub or a self
powered USB hub.
The power descriptor in the internal MTP memory of the FT231X should be programmed to a value of
zero (self powered).
In order to comply with the first requirement above, the USB bus power (pin 1) is used to control the
VBUS_Sense pin of the FT220X device. When the USB host or hub is powered up an internal 1.5kΩ
resistor on USBDP is pulled up to +3.3V, thus identifying the device as a full speed device to the USB
host or hub. When the USB host or hub is powered off, VBUS_Sense pin will be low and the FT220X is
held in a suspend state. In this state the internal 1.5kΩ resistor is not pulled up to any power supply
(hub or host is powered down), so no current flows down USBDP via the 1.5kΩ pull-up resistor. Failure to
do this may cause some USB host or hub controllers to power up erratically.
Figure 6.2 illustrates a self powered design which has a +3.3V to +5.25V supply.
Note:
1. When the FT231X is in reset, the UART interface I/O pins are tri-stated. Input pins have internal
200kΩ pull-up resistors to VCCIO, so they will gently pull high unless driven by some external
logic.
Copyright © 2013 Future Technology Devices International Limited
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