FT232RL-REEL FTDI, FT232RL-REEL Datasheet - Page 25

• Manufacturer Part Number: FT232RL-REEL
• Description: USB Interface IC USB to Serial UART Enhanced IC SSOP-28
• Manufacturer: FTDI
• Type: USB to UARTr

Specifications of FT232RL-REEL

• Maximum Operating Temperature: 85 C
• Minimum Operating Temperature: -40 C
• Mounting Style: SMD/SMT
• Supply Current: 15 mA
• Operating Supply Voltage: 3.3 V to 5.25 V
• Package / Case: SSOP 5.3mm x 10.28mm
• Description/function: USB to Serial UART Enhanced IC SSOP-28
• Operating Temperature Range: - 40 C to + 85 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

6.3 USB Bus Powered with Power Switching Configuration
Figure 6.3 Bus Powered with Power Switching Configuration
A requirement of USB bus powered applications, is when in USB suspend mode, the application draws a
total current of less than 2.5mA. This requirement includes external logic. Some external logic has the
ability to power itself down into a low current state by monitoring the PWREN# signal. For external logic
that cannot power itself down in this way, the FT232R provides a simple but effective method of turning
off power during the USB suspend mode.
Figure 6.3 shows an example of using a discrete P-Channel MOSFET to control the power to external
logic. A suitable device to do this is an International Rectifier (www.irf.com) IRLML6402, or equivalent. It
is recommended that a “soft start” circuit consisting of a 1kΩ series resistor and a 0.1μF capacitor is used
to limit the current surge when the MOSFET turns on. Without the soft start circuit it is possible that the
transient power surge, caused when the MOSFET switches on, will reset the FT232R or the USB host/hub
controller. The soft start circuit example shown in Figure 6.3 powers up with a slew rate of
approximaely12.5V/ms. Thus supply voltage to external logic transitions from GND to +5V in
approximately 400 microseconds.
As an alternative to the MOSFET, a dedicated power switch IC with inbuilt “soft-start” can be used. A
suitable power switch IC for such an application is the Micrel (www.micrel.com) MIC2025-2BM or
equivalent.
With power switching controlled designs the following should be noted:
i)
ii) Set the Pull-down on Suspend option in the internal FT232R EEPROM.
iii) One of the CBUS Pins should be configured as PWREN# in the internal FT232R EEPROM, and used
iv) For USB high-power bus powered applications (one that consumes greater than 100mA, and up
v) PWREN# gets its VCC from VCCIO. For designs using 3V3 logic, ensure VCCIO is not powered
SHIELD
The external logic to which the power is being switched should have its own reset circuitry to
automatically reset the logic when power is re-applied when moving out of suspend mode.
to switch the power supply to the external circuitry. This should be pulled high through a 10 kΩ
resistor.
to 500mA of current from the USB bus), the power consumption of the application must be set in
the Max Power field in the internal FT232R EEPROM. A high-power bus powered application uses
the descriptor in the internal FT232R EEPROM to inform the system of its power requirements.
down using the external logic. In this case use the +3V3OUT.
5
100nF
1
2
3
4
10nF
Copyright © 2010 Future Technology Devices International Limited
GND
+
4.7uF
Ferrite Bead
GND
5V VCC
+
P-Channel Power
5V VCC
MOSFET
s
g
d
0.1uF
1K
Soft Start
100nF
GND
Circuit
0.1uF
OSCI
OSCO
USBDM
USBDP
VCCIO
RESET#
NC
3V3OUT
VCC
NC
FT232R USB UART IC Datasheet Version 2.07
A
G
N
D
G
N
D
FT232R
G
N
D
GND
G
N
D
Switched 5V Power
T
E
S
T
To External Logic
CBUS0
CBUS1
CBUS2
CBUS3
CBUS4
DTR#
DSR#
DCD#
RTS#
CTS#
RXD
TXD
RI#
PWREN#
Document No.: FT_000053
Clearance No.: FTDI# 38
5V VCC
10K
25