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Copyright © 2012 Future Technology Devices International Limited

UMFT231XE

Version 1.0

Document Reference No.: FT_000652

Clearance No.: FTDI#

294

5.5

Variable IO Voltage Supply

MCU

Vcc = 1.8V

– 3.3V

TXD

RXD

RTS#

CTS#

GND

TXD

RXD

RTS#

CTS#

Jumper JP2 - Closed

Jumper JP1 - Open

GND

VCCIO

3V3OUT

VBUS

VCC

Figure 5.4 – USB Bus Powered 3.3V Logic Drive

The FT231X can process signals at CMOS/TTL logic levels in the range of 1.8V to 3.3V. This section

describes how to utilise this feature.

Figure 5.4 shows a configuration where the FT231X is interfaced to a device with IOs operating in the

range of 1.8V - 3.3V. The IO ports of this module need to be powered with a voltage level that is equal to

the level of the signals it is processing. Since the FT231X‟s embedded voltage regulator only outputs 3V3

the IO ports will need to be powered from another power source when operating at voltage levels other

than 3.3V.

By default, a short is present between 3V3OUT (embedded voltage regulator) and VCCIO (IO port‟s

power input with the connection made by JP1. If an external power supply is used to power the IO ports

this jumper needs to be open.

The configuration described in this section can be implemented in either bus-powered mode or self-

powered mode.

Note 1: The CBUS and DBUS pins are 5V tolerant; however these signals cannot drive signals at 5V

TTL/CMOS. VCCIO is not 5V tolerant; applying 5V to VCCIO will damage the chip.

Note 2: If power is applied to VCCIO and no power is applied to VCC all IOs will be at an unknown state,

this however will not damage the chip. The FT231X also has protective circuitry to prevent the chip being

damaged by a voltage discrepancy between VCCIO and the level of the signal being processed.

Note 3: When using VCCIO less than 3V3 on a chip from FTDI‟s X-chip range, it is recommended to use

pull up resistors (47K) to VCCIO on the data lines, all of the UMFT2xxXE devices include an on-board

pull-up for these lines.