UMFT240XE Datasheet, PDF (11/18 Pages) Future Technology Devices International Ltd. – UMFT240XE USB to 8-bit 245 FIFO Development Module

UMFT240XE
Version 1.0
Document Reference No.: FT_000653 Clearance No.: FTDI# 295
5.5 Variable IO Voltage Supply
Vcc = 1.8V – 3.3V
MCU
DATA0-7
RXF#
TXE#
RD#
WR#
GND
GND
VCCIO
3V3OUT
VCC
VBUS
Jumper JP1 - Open
Jumper JP2 - Closed
Figure 5.4 – USB Bus Powered 3.3V Logic Drive
The FT240X 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 FT240X 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 FT240X‟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 FT240X 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 uses
pull up resistors (47K) to VCCIO on the data lines, all of the UMFT2xxXE devices include an on-board
pull-up for these lines.
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