FT234XD-T FTDI, FT234XD-T Datasheet - Page 21

• Manufacturer Part Number: FT234XD-T
• Description: USB Interface IC USB to Basic Serial UART IC
• Manufacturer: FTDI

Specifications of FT234XD-T

• Rohs: yes
• Product: USB 2.0
• Interface Type: UART, USB
• Operating Supply Voltage: 3.3 V to 5.25 V
• Operating Supply Current: 8 mA
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: DFN-12
• Minimum Operating Temperature: - 40 C

6.2 Self Powered Configuration
Figure 6.2 Self Powered Configuration
Figure 6.2 illustrates the FT234XD 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 –
The power descriptor in the internal MTP memory of the FT234XD 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 FT2234XD 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 FT234XD 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:
i)
ii) A self powered device can use as much current as it needs during normal operation and USB
iii) A self powered device can be used with any USB host, a bus powered USB hub or a self powered
1. When the FT234XD is in reset, the UART interface I/O pins are tri-stated. Input pins have internal
100nF
A self powered device should not force current down the USB bus when the USB host or hub
controller is powered down.
suspend as it has its own power supply.
USB hub.
75kΩ pull-up resistors to VCCIO, so they will gently pull high unless driven by some external
logic.
SHIELD
5
100nF
Copyright © 2013 Future Technology Devices International Limited
GND
1
2
3
4
VCC
+
GND
10k
4k7
4.7uF
GND
47pF
GND
VCC(3.3-5.25V)
47pF
GND
Document No.: FT_000753 Clearance No.: FTDI#324
27R
27R
FT234XD USB TO BASIC UART IC
100nF
USBDM
VBUS_SENSE
USBDP
VCC
VCCIO
RESET#
3V3OUT
FT234XD
Version 1.1
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