Designing Hardware for QuickUSB
Designing Hardware for QuickUSB
Connecting QuickUSB to your hardware is simple. First, decide on the type of
connection you need. If you need to transfer large amounts of data very quickly,
then you should use the High Speed Parallel Port. If you only need to turn some
I/O pins on and off, you can just use the general-purpose I/O pins.
The Cypress EZ USB FX2
QuickUSB is based on the Cypress EZ-USB FX2LP microcontroller. The FX2LP is
a powerful, single-chip USB microcontroller that offers an unparalleled capability
to interface subsystems to a PC with a high-speed USB 2.0 connection.
QuickUSB unleashes the power of the FX2LP to high-level hardware and
software designers by abstracting its capabilities as library of dataflow oriented
function calls. In addition, chip-specific capabilities are supported via ‘Settings’
that allow the user to customize the behavior of the FX2LP to suit the target
application.
Power and Ground
QuickUSB supplies unreg5V at up to 400 mA max on the VBUS pins to
power your circuitry. For modules Rev A1 and above, an FET on the QuickUSB
module controls power. Power is off by default and then turned on once the
host configures the module. This behavior is required by the USB specification.
The QuickUSB module incorporates a current limiting circuit that will shut down
the VBUS pins on an over-current condition. In addition the entire module may
be powered down by the host or a USB hub if it draws more than the 500 mA
allotted by the USB.
If your circuit draws less than 400 mA, you may power it from the unregulated
5V provided on the VBUS pins. However, if your circuit will draw more than 50
mA, you should design your circuit with either a downstream power switch (such
as the TPS2051A) or an active high enable logic switched voltage regulator.
Connect the enable signal to SW_PG (pin 76). This signal will enable your
circuit’s voltage regulator once the VBUS switch is turned on and the output
voltage has stabilized to >= 93% of the voltage supplied by the USB. For more
information about the QuickUSB VBUS switch, consult the datasheet for the
Texas Instruments TPS2150.
If your circuit draws more than 400 mA, do not power it from VBUS. It should be
powered with an external power supply and connect the digital ground of your
circuit to GND. In this case, you might want to connect an unused I/O pin to the
external power supply through a current limiting resistor (10K) so you can read
the pin to determine the state of the external power supply.
The Cypress EZ USB FX2
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