UM232R FTDI, UM232R Datasheet - Page 20
![Interface Modules & Development Tools USB to Serial UART Dev Mod for FT232R](/photos/15/89/158917/um232r_sml.jpg)
UM232R
Manufacturer Part Number
UM232R
Description
Interface Modules & Development Tools USB to Serial UART Dev Mod for FT232R
Manufacturer
FTDI
Type
Development Moduler
Specifications of UM232R
Interface Type
USB, Serial, UART
Data Bus Width
Serial
Operating Supply Voltage
1.8 V to 5.25 V
Product
Interface Modules
Supported Devices
FT232R
Svhc
No SVHC (18-Jun-2010)
Development Tool Type
Development Kit
Kit Features
Single Chip USB To Asynchronous Serial Data Transfer Interface, Auto Transmit Buffer
Rohs Compliant
Yes
Supported Families
FT232RL
Features
Single Chip USB To Asynchronous Serial Data Transfer Interface, Auto Transmit Buffer Control
Tool / Board Applications
USB To
For Use With/related Products
FT232R
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
7.3 USB Bus Powered with Power Switching Confiduration
Figure 7.3 Bus Powered with Power Switching Configuration
USB Bus Powered circuits need to be able to power down in USB suspend mode in order to meet the
<=500μA total USB suspend current requirement (including external logic). Some external can 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 way of turning off power to external circuitry
during USB suspend.
Figure 7.3 shows how to use a discrete P-Channel Logic Level MOSFET to control the power to external logic
circuits. A suitable device would be an International Rectifier (www.irf.com) IRLML6402, or equivalent. It is
recommended that a “soft start” circuit consisting of a 1kΩseries resistor and a 0.1μF capacitor are used to
limit the current surge when the MOSFET turns on. Without the soft start circuit there is a danger that the
transient power surge of the MOSFET turning on will reset the FT232R, or the USB host / hub controller.
The values used here allow attached circuitry to power up with a slew rate of ~12.5V per millisecond, in
other words the output voltage will transition from GND to 5V in approximately 400 microseconds.
Alternatively, a dedicated power switch I.C. with inbuilt “soft-start” can be used instead of a MOSFET. A
suitable power switch I.C. for such an application would be a Micrel (www.micrel.com) MIC2025-2BM or
equivalent.
Please note the following points in connection with power controlled designs:
© Copyright 2009 Future Technology Devices International Ltd
iv) For USB high-power bus powered device (one that consumes greater than 100mA, and up to 500mA
iii) One of the CBUS Pins should be configured as PWE# in the internal EEPROM, and should be used to
ii) Set the Pull-down on Suspend option in the internal EEPROM.
i) The logic to be controlled must have its own reset circuitry so that it will automatically reset itself
when power is applied on coming out of suspend.
switch the power supply to the external circuitry.
of current from the USB bus), the power consumption of the device should be set in the max power
field in the internal EEPROM. A high-power bus powered device must use this descriptor in the
internal EEPROM to inform the system of its power requirements.
MCU
TXD
RXD
RTS#
CTS#
UM232R USB - Serial UART Development Module Incorporating Clock Generator
CTS#
GND
TXD
RTS# 3
RXD
10
12
7
1
5
J1
UM232R
1
J2
©
2
FTDI 2008
2
3
1
Document Reference No.: FT_000051
(PWREN#)
14
13
24
18
USB
CB3
Clearance No.: FTDI# 125
P-Channel Power
Datasheet Version 1.04
MOSFET
s
g
1K
d
Circuit
Start
Soft
0.1uF
0.1uF
19