DS_FT2232D Datasheet, PDF (22/61 Pages) List of Unclassifed Manufacturers – Future Technology Devices International Ltd

Document No.: FT_000173
FT2232D DUAL USB TO SERIAL UART/FIFO IC Datasheet
Version 2.05
Clearance No.: FTDI# 127
6.1 USB Self Powered Configuration
Figure 6.2 Self Powered Configuration
Figure 6.2 illustrates the FT2232D in a typical USB self powered configuration. A USB Self
Powered device gets its power from its own POWER SUPPLY and does not draw current from the
USB bus. The basic rules for USB Self power devices are as follows –
a) A Self-Powered device should not force current down the USB bus when the USB
Host or Hub Controller is powered down.
b)A Self Powered Device can take as much current as it likes during normal operation
and USB suspend as it has its own POWER SUPPLY.
c)A Self Powered Device can be used with any USB Host and both Bus and Self
Powered USB Hubs.
The USB power descriptor option in the EEPROM should be programmed to a value of zero (self powered).
To meet requirement a) the 1.5 K pull-up resistors on USBDP is connected to RSTOUT# as per the bus-
power circuit. However, the USB Bus Power is used to control the RESET# Pin of the FT2232D device. When
the USB Host or Hub is powered up RSTOUT# will pull the 1.5K resistor on USBDP to 3.3V, thus identifying
the device as a full speed device to USB. When the USB Host or Hub power is off, RESET# will go low and
the device will be held in reset. As RESET# is low, RSTOUT# will also be low, so no current will be forced
down USBDP via the 1.5K pull-up resistor when the host or hub is powered down. Failure to do this may
cause some USB host or hub controllers to power up erratically. Note: When the FT2232D is in reset, the
I/O interface pins all go tri-state. These pins have internal 200K pull-up resistors to VCCIO, so they will
gently pull high unless driven by some external logic.
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