Belkin XM Commander Especificações descarregar pdf (Página 49)

REF: BB_SRM_xM BeagleBoard-xM System

Reference Manual

Revision A2

Page 49 of 164

in the OTG or Host modes. As this is limited to 100mA, a powered hub must be used to

support peripherals on the OTG port.

It is possible to provide 5V via the expansion connectors as would be the case from a

daughter card to prevent you from having to have two DC supplies. You should be

careful in doing this. If you plan to use the USB OTG port, you will need to place an

unconnected connector into the DC power jack to insure that the DC from the OTG port

is not shorted to the 5V supplied via the expansion connector. There is a signal called

nUSB_POWER which if Hi (5V) indicates that there is 5V supplied by the USB OTG

port, it is plugged in, and the DC dummy jack is installed. This condition could be used

on the daughtercard to know that it is OK to supply power onto the expansion bus to

power the board. If this signal is low, then that indicates that there is no DC power

connected and there is no USB OTG port connected. For this reason, is recommended

however, that a large pullup be provided on the daughtercard to make the signal HI (5V)

to detect the true state of the DC jack. It is always possible that at any point a USBOTG

cable could be installed. This means that in order to power the board from the expansion

headers, the DC dummy jack must be installed and there is a method to verify that

condition.

8.3.4 AUX 3.3V Supply

The TPS2141 has an integrated 3.3V LDO which is being used to supply the 3.3V as

required on the BeagleBoard for the DVI-D interface and the UART. The input to the

LDO is supplied by the main DC_5V. This insures that the power to the LDO can be

supplied by either the USB or the DC wall supply and that the current measurement

includes the 3.3V supply. The 3.3V supply can be turned off by activating GPIO1 on the

TPS65950 to a 1. By default the voltage is on. You will also see that the 3.3V supply

powers the power LED, D5. If during a low power mode, the user chooses to turn of the

power LED, this GPIO pin can be used to turn off the power LED. It should also be

noted, that the 3.3V rail controls the serial port power, so this will be powered down as

well. Figure 22 is the AUX 3.3V Supply design.

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Belkin XM Commander Especificações Página 49