UMFT240XE-01 FTDI, UMFT240XE-01 Datasheet - Page 10

• Manufacturer Part Number: UMFT240XE-01
• Description: Interface Development Tools USB to 8-Bit 245 FIFO Module
• Manufacturer: FTDI
• Type: USB to FIFOr
• Series: FT240Xr

Specifications of UMFT240XE-01

• Rohs: yes
• Product: Development Modules
• Tool Is For Evaluation Of: FT240XQ
• Interface Type: I2C, FIFO, USB
• Operating Supply Voltage: 3.3 V
• Description/function: USB to 8bit 245 FIFO evaluation module
• Dimensions: 29.02 mm x 19.24 mm x 9.2 mm
• Operating Supply Current: 1 A
• Factory Pack Quantity: 25
• For Use With: FT240XQ

5.4
Figure 5.3 – Bus Powered with Power Switching Configuration
USB bus powered mode is introduced in Section 5.2. This section describes how to use bus-powered
mode with a power switch.
USB bus powered circuits are required by USB compliance standards to consume less than 2.5mA (and
less than 100mA when not enumerated and not suspended) when connected to a host or hub when in
USB suspend mode. The PWREN# CBUS function can be used to remove power from external circuitry
whenever the FT240X is not enumerated. (Note: It is impossible to be in suspended mode when
enumerated.)(Note that Figure 5.3 is for illustration only and that the pins do not actually go all the way
through the PCB)
To implement a power switch using PWREN#, configure a P-Channel Power MOSFET to have a soft start
by fitting a 10K pull-up, a 1K series resistor and a 100nF cap as shown in Figure 5.3.
Connecting the source of the P-Channel MOSFET to 3V3OUT instead of VBUS can allow external logic to
source 3.3V power from the FT240X without breaking USB compliancy. In this setup it is important that
the VCCIO is not sourced from the drain of this MOSFET, this is because the power used to drive the gate
of this transistor is sourced from VCCIO. VCCIO should be connected directly to 3V3OUT for this setup to
function effectively. It is also important that the external logic must and IO core of the FT240X must not
draw more that 50mA, this is because the current limit of the internal 3.3V regulator is 50mA.
USB Bus Powered with Power Switching Configuration
MCU
VCC
5V
DATA0-7
RXF#
TXE#
Jumper JP1 - Closed
WR#
RD#
3.3V TTL Mode
GND
Self-Sorced
Copyright © 2012 Future Technology Devices International Limited
3V3OUT
VCCIO
Document Reference No.: FT_000653
VBUS
VCC
Jumper JP2 - Closed
CBUS5
PWREN#
Bus Powered
10K
Mode
P-Channel Power
1K
MOSFET
s
g
Clearance No.: FTDI#
d
10
Circuit
Start
Soft
UMFT240XE
0.1uF
Version 1.0
0.1uF
295