Digilent 410-302P-KIT - Manual (Page 4)

WiFire Reference Manual
The header connector J4 provides access to the other serial handshaking signals provided by the FT232RQ.
Connector J4 is not loaded at the factory and can be installed by the user to access these signals.
3 Power Supply
The WiFire is designed to be powered via USB (J1), from an external power supply (J14 or J15), or from the USB
OTG receptacle (J11). Jumper block J16 is used to select which power supply is used. The power supply voltage
selected by J16 is applied to the unregulated power bus, VU.
In order to operate the WiFire as a USB device powered from the USB serial interface (connector J1), place a
shorting block in the UART position of jumper block J16. To operate the WiFire from an external power supply,
attach the power supply to either J14 or J15 and place a shorting block in the EXT position of J16. Be sure to
observe correct polarity when connecting a power supply to J14, as a reversed connection could damage the
board. To operate the WiFire as a USB powered device from the USB OTG connector (J11), place a shorting block
on the USB position of J16. This will normally only be done when running a sketch on the board that programs it to
operate as a USB device. The power supply section in the WiFire provides two voltage regulators, a 3.3V regulator
and a 5V regulator. All systems on the WiFire board itself operate at 3.3V and are powered by the 3.3V regulator.
The 5V regulator is used to provide power for external circuits, such as shields, that require 5V for operation and to
supply USB 5.0V when the WiFire is used as a USB Host. The 5V regulator can be completely disabled if it is not
needed for a given application.
When a shield is used, connector J5 provides power to the shield. Connector J5 pin 8 provides VIN as applied by
the external power source J14 or J15. If no power is provided to J14 or J15, VIN will not be powered. For most
shields, pin 5 on connector J5 would provide 5.0V to the shield; however, the WiFire is not 5v tolerant and it would
be very easy for a shield to destroy an input if 5.0V were applied to the PIC32MZ. For this reason, JP9 was added to
control the voltage supplied to the shield’s 5V source. By default, JP9 is loaded to supply only 3.3V on the 5.0V pin
so that the shield does not get 5V and thus cannot inadvertently apply 5.0V to any input to the WiFire. If the shield
requires 5.0V to operate, the shield will not work when 3.3V is applied; JP9 must be selected to provide 5.0V for
the shield to work. However, extreme caution should be used when selecting 5.0V on JP9 to ensure that the shield
will observe IOREF and not supply 5.0V to any input to the WiFire; as this will damage the input to the PIC32MZ on
the WiFire.
The WiFire board is designed for low power operation and efficient use of battery power; a switching mode
voltage regulator is used for the 3.3V power supply. This switching mode regulator is made up of a Microchip
MCP16301 and associated circuitry, which can operate on input voltages from 4V to 30V with up to 96% efficiency,
and is rated for 600mA total current output. The MCP16301 has internal short circuit protection and thermal
protection. The 3.3V regulator takes its input from the unregulated power bus, VU, and produces its output on the
VCC3V3 power bus. The VCC3V3 bus provides power to all on-board systems and is available at the shield power
connector (J5) to provide 3.3V power to external circuitry, such as shields.
The 5V regulator section provides a low dropout linear regulator. The 5.0 regulator is provided for powering
external circuitry that needs a 5V power supply, such as providing for USB 5.0V when the WiFire is used as a USB
host, or to provide 5.0V to the shield on J5 with JP9 selected to 5.0v. This voltage regulator uses an On
Semiconductor NCP1117LP. The NCP1117LP is rated for an output current of 1A. The dropout voltage of the
NCP1117LP is a maximum of 1.4V at 1A output current. The maximum input voltage of the NCP1117LP is 18V. The
recommended maximum operating voltage is 15V. However, if the 5.0V regulator is completely disable by
removing all jumpers on J17, the external input voltage applied to J14 or J15 may be as high as the 30V as limited
by the switching mode 3.3V regulator.
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