Datasheet

chipKIT™ Wi-FIRE™ Board Reference Manual

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Page 10 of 24

The Wi-FIRE can be operated as a self-powered device or as a bus powered device from either the USB serial

connector (J1) or the USB OTG/device connector (J11).

For operation as a self-powered device, place a shorting block on the EXT position of J16 and connect a suitable

external power supply to either J14 or J15.

To operate the Wi-FIRE as a bus powered device powered from the USB serial connector (J1), place a shorting

block in the UART position of J16. To operate as a bus powered device powered from the OTG/device connector

(J11), place a shorting block in the USB position of J16.

Note that there are two completely independent USB interfaces on the Wi-FIRE board, and it is possible for the Wi-

FIRE to appear as two different USB devices at the same time. These two devices can be connected to two

different USB ports on the same host, or to USB ports on two different hosts. If the Wi-FIRE board is connected to

two different USB hosts simultaneously, there will be a common ground connection between these two hosts

through the Wi-FIRE board. In this case, it is possible for ground current to flow through the Wi-FIRE board,

possibly damaging one or the other USB host if they do not share a common earth ground connection.

When the Wi-FIRE is operating as a bus powered device using USB connector J1, it will appear as a self-powered

device from the perspective of a USB host connected to J11. Similarly, when operating as a bus powered device

from connector J11, it will appear as a self-powered device from the perspective of connector J1.

A USB host is expected to be able to provide bus power to USB devices connected to it. Therefore, when operating

as a USB host, the Wi-FIRE should normally be externally powered. Connect a power supply to the external power

connector, J17. It is possible to operate the Wi-FIRE as a USB host powered from USB connector J1; however, in

this case the host USB port will be providing power for the Wi-FIRE as well as the USB device connected to the Wi-

FIRE. In this case, ensure that the total load does not exceed the 500mA maximum load that a USB device is

allowed to present to the host.

The USB host provides regulated 5V power to the connected USB device. The internal 5V LDO regulator can be

used to provide the USB power when operating from an external power supply. Place shorting blocks on jumper

block J17, as described above in the power supply section.

If the external power supply being used is a regulated 5V supply, place a shorting block between pins VU and 5V0

on connector J17, as described above in the power supply section to bypass the on board 5.0V regulator.

The power supply used must be able to supply enough current to power both the Wi-FIRE and the attached USB

device, since the Wi-FIRE provides power to the attached USB device when operating as a host. The USB 2.0

specification requires that the host provide at least 100mA to the device.

Jumper JP6 is used to provide the required USB host capacitance to the host connector being used. Place the

shorting block in the “A” position when using the standard USB type A (host) Connector (J12). Place the shorting

block in the “AB” position for use with the USB micro-AB (OTG) connector (J11).

With JP8 shorted, chipKIT pin 25 drives the enable input of a TPS2051B Current-Limited Power Distribution Switch

to supply 5V USB power to the host connector. This switch has over-current detection capability and provides an

over-current fault indication by pulling the signal USBOC low. The over-current output pin can be monitored via

the chipKIT pin 8 (RA14/INT3) when JP7 is shorted. Details about the operation of the TPS2051B can be obtained

from the datasheet available at www.ti.com.

When using the Wi-FIRE outside the MPIDE environment, the Microchip Harmony Library provides USB stack code

that can be used with the board. There are reference designs available on the Microchip website demonstrating