■ PHOTO 2. There is nothing new and exciting here. It looks to be just another
500 mA LDO voltage regulator with shutdown, surrounded by the normal
complement of filter capacitors.
tying the A-side enable pin logically
high. If a USB power fault occurs, the
LED attached to the B-side error flag
pin is illuminated. Otherwise, the
VBUS power LED glows bright green.
The business end of this
evaluation kit can be seen in the
aerial reconnaissance shot
represented by Photo 4. If I had to
guess, I would say that the FT311D is
a chunk of Vinculum specifically
programmed to perform the
USB/Android bridge function. The
reason I think this way is swayed by
the presence of the 12 MHz crystal.
If you examine the USB host
portal hardware, it smells heavily of
the FT232R USB-to-RS-232
converters. The FT311D’s internal
identification EEPROM can also be
modified in a similar fashion to that
of the FT232R.
There is a programming port (J7)
that is used to load the FT311D’s
operational ROM. The FT311D’s
similarity to the FT232R takes much
of the pain out of the hardware
■ PHOTO 3. The AIC1526 dual USB high-side power switch is a better choice
here than a no-frills P-channel MOSFET.
for use in USB power systems. The
AIC1526 can switch 500 mA
continuously on each of its two
channels, and both channels include
safeguards such as current limiting,
short-circuit protection, thermal
62 April 2013
shutdown, and undervoltage lockout.
The USB host evaluation kit
utilizes the B portion of the AIC1526.
The B-side MOSFET is permanently
activated by grounding the B-side
enable pin. The A-side is disabled by
Take another look at Photo 1.
Note that there aren’t any
superfluous LEDs or pushbuttons.
Everything on the kit main board
means business. The resident LEDs
are used to display power and
operational status. The jumper blocks
are used to select the desired I/O
mode. It’s easy to see that the
FT311D’s I/O pins are feeding the
female headers, as well as the double
row of male headers just above the