Datasheet

chipKIT™ Wi-FIRE™ Board Reference Manual

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Page 5 of 24

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 Wi-FIRE 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 Wi-FIRE. 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 Wi-FIRE; as this will damage the input to the

PIC32MZ on the Wi-FIRE.

The Wi-FIRE 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 Wi-FIRE 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.

The input voltage to the 5V regulator is taken from the VU bus, and the output is placed on the VCC5V0 power bus.

There is a reverse polarity protection diode in the external power supply circuit. Considering the diode drop plus

the forward drop across the regulator, the minimum input voltage to the regulator should be 7V to produce a

reliable 5V output.

For input voltages above 9V, the regulator will get extremely hot when drawing high currents. The NCP1117LP has

output short circuit protection as well as internal thermal protection and will shut down automatically to prevent

damage.

The 5V regulator selection on JP17 provides four 5V power configurations:

1) 5V regulator completely disabled and no 5V power available;

2) 5V regulator bypassed and 5V provided from an external 5V power supply, such as USB;

3) on-board 5V regulator used to provide 5V power;

4) External 5V regulator used to regulate VU and provide 5V power.

Jumper block J17 is used to select these various options and the following diagrams describe the use of J16. This

diagram shows the arrangement of the signals on J17:

LDO OutLDO In

VU 5V0

GNDEN Ext