Vinculum-II Embedded Dual USB Host Controller IC;
Vinculum-II IDE; FT232RL: www.ftdichip.com
projects. The TC1262-3.3 LDO is capable of supplying
loads up to 500 mA with a typical dropout voltage of 350
mV at full load. Designed for use in battery-powered
applications, this voltage regulator can operate reliably
with a pair of 1.0 µF ceramic capacitors attached to its
input and output pins. Recall my First Law of Embedded
Computing which states, “Nothing is free.” There is a
“price” to pay for the TC1262-3.3 LDO voltage regulator’s
feature set. In this case, the price is cheap as it only costs
us 80 µA of power supply current to use it in our designs.
The TC1262-3.3 LDO input must be able to accept
voltage from the USB portal and from an external source.
If we decide to run the Vinculum-II in host mode, we’ll
need to supply the VBUS voltage at the host USB
connector in the same manner your PC USB portals
supply VBUS power to downstream devices. Our voltage
regulator design is laid out in Schematic 2.
■ SCREENSHOT 5. Folks from the planet Krypton have an
advantage over us Earthlings as they can check the top
and bottom of their ExpressPCB layouts simultaneously.
included to keep those nasty little sparks that tend to
bridge electronic components and your fingertips from
doing some unwanted soldering inside of the Vinculum-II
IC. The ferrite beads FB1 and FB2 are in position to thwart
EMI that may try to creep into the 5 volt supply.
VINCULUM-II CORE DESIGN
HOST INTERFACE DESIGN
If you study Schematics 2 and 3, you will conclude
that any host USB interface has the ability to supply VBUS
power to the TC1262-3.3 LDO. However, it is not
politically correct to power a host USB portal externally.
For instance, you wouldn’t want to attempt to force VBUS
power from an external downstream USB device into the
USB portal of your thousand-dollar laptop. So, when
operating as a host, the presence of the HOST JMPR x
provides an electrical path to provide 5.0 volts to the
downstream USB device. Since the host provides VBUS
via its USB interface, 5.0 volts will probably be supplied
externally. That means we need to provide an electrical
path between the external 5.0 volt power supply
and the input of the voltage regulator. This is easily
accomplished by installing the 5V0 JMPR. Note that
the VBUS JMPR and 5V0 JMPR are mutually
exclusive as it pertains to having those jumpers
installed. Our embedded dual USB host controller
supports a pair of USB host portals which are
identified as P0 and P1. The USB portals drawn up
in Schematic 3 are standard fare for most FTDI
parts. ESD suppressors CR1, CR2, CR3, and CR4 are
Like many of today’s low voltage core microcontrollers,
the Vinculum-II needs supporting electrical components
for its internal voltage regulators. Pins 3 and 7 of the
Vinculum-II IC grinning in Photo 2 form the business
end of the Vinculum-II’s internal 1.8 volt power system.
The 1.8V VCC PLL IN (pin 3) acts as the +1.8 volt supply
to the internal clock multiplier. A 100 nF capacitor must
be attached between this pin and ground. The output of
the internal +1.8 volt regulator emanates from pin 7 of the
Vinculum-II. Schematic 3 shows a pair of filter capacitors
hanging from the +1.8 volt output pin. Take another look
at Schematic 3 and you’ll see a ferrite bead standing
guard on the internal clock multiplier +1.8 volt input pin.
■ PHOTO 1. Rising from concept to reality, the EDTP
Vinculum-II debug module.
■ SCHEMATIC 2.
If you’re a regular
Nuts & Volts
here either. The
is a solid and
part shown here
in a field tested
September 2010 63