UM232R FTDI, UM232R Datasheet - Page 15

• 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

Figure 6 - 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 logic 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 6 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 1kΩ series 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 –
i)
ii) Set the Pull-down on Suspend option in the internal EEPROM.
iii) One of the CBUS Pins should be configured as PWE# in the internal EEPROM, and should be used to switch the
iv) For USB high-power bus powered device (one that consumes greater than 100mA, and up to 500mA of current
v) For 3.3V power controlled circuits the FT232R’s VCCIO pin must not be powered down with the external circuitry
UM232R USB-Serial UART Development Module Datasheet Version 1.02
The logic to be controlled must have its own reset circuitry so that it will automatically reset itself when power is re-
applied on coming out of suspend.
power supply to the external circuitry.
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.
(the PWREN# signal gets its VCC supply from VCCIO). Either connect the power switch between the output of the
3.3V regulator and the external 3.3V logic or power VCCIO from the 3V3OUT pin of the FT232R.
6.3 USB Bus Powered with Power Switching Configuration
MCU
Switched 5V Power
to External Logic
RTS#
CTS#
TXD
RXD
CTS# 10
RTS# 3
GND 7
RXD 5
TXD 1
12
J1
J2
© Future Technology Devices International Ltd. 2005
(PWREN#)
13
14 USB
24
18 CB3
P-Channel Power
MOSFET
s
g
1k
d
Circuit
Start
Soft
0.1 uF 0.1 uF