UMFT231XE
Version 1.0
Document Reference No.: FT_000652 Clearance No.: FTDI# 294
5.6 3.3V Voltage Supply
Vcc = 3.3V
Vcc = 3.3V
TXD
RXD
TXD
RTS#
CTS#
RXD
RTS#
CTS#
GND
MCU
VCCIO
VCC
3V3OUT
VBUS
GND
Jumper JP2 - Open
Jumper JP1 - Closed
Figure 5.5 – USB Self Powered 3.3V Logic Drive
The FT231X can be powered from a single 3.3V supply. This feature is an alternative to having the
FT231X powered at 5V in standard self-powered configuration.
The 3.3V Self Powered configuration is illustrated in Figure 5.5. Note that the 3.3V input is connected to
VCC, VCCIO and 3V3OUT.
5.7 Configuring the MTP ROM
The FT231X contains an embedded MTP ROM. This can be used to configure the functions of each CBUS
pin, the current drive on each signal pin, current limit for the USB bus and the other descriptors of the
device. For details on using the MTP ROM/EEPROM programming utility FT_PROG, please see the
FT_PROG User Guide.
When programming the MTP ROM please note:
i) One of the CBUS Pins can be configured as PWREN# in the internal MTP ROM. This can be used to
switch the power supply to the external circuitry.
ii) The Max Bus Power setting of the MTP ROM should specify the maximum current to be drawn from
the USB host/hub when enumerated. For high-powered USB devices the current limit when
enumerated is between 100mA and 500mA, for low-powered USB devices the current limit is
100mA.
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