User Manual

8.6 Cape Power
This section describes the power rails for the capes and their usage.
8.6.1 Main Board Power
The Table 20 describes the voltages from the main board that are available on the
expansion connectors and their ratings. All voltages are supplied by connector P9 . The
current ratings listed are per pin.
Table 20
Expansion Voltages
Current Name P9 Name Current
GND
1 2
GND
250mA VDD_3V3B
3 4
VDD_3V3B 250mA
1000mA
VDD_5V
5 6
VDD_5V
1000mA
250mA SYS_5V 7 8 SYS_5V 250mA
: :
GND
43
44
GND
GND
45 46
GND
The VDD_3V3B rail is supplied by the LDO on the element14 BeagleBone Black and is
the primary power rail for expansion boards. If the power requirement for the capes
exceeds the current rating, then locally generated voltage rail can be used. It is
recommended that this rail be used to power any buffers or level translators that may be
used.
VDD_5V is the main power supply from the DC input jack. This voltage is not present
when the board is powered via USB. The amount of current supplied by this rail is
dependent upon the amount of current available. Based on the board design, this rail is
limited to 1A per pin from the main board.
The SYS_5V rail is the main rail for the regulators on the main board. When powered from
a DC supply or USB, this rail will be 5V. The available current from this rail depends on
the current available from the USB and DC external supplies.
8.6.2 Expansion Board External Power
A cape can have a jack or terminals to bring in whatever voltages may be needed by that
board. Care should be taken not to let this voltage feedback into any of the expansion
header pins.
It is possible to provide 5V to the main board from an expansion board. By supplying a