USB power up problem, OMAP 3530 (beagle board)

hi all

we are working on Beagle board.
we are customizing the board for some specific applications, we are
interfacing NAND flash,
LPDDR SDRAM, and CPLD to the OMAP 3530 Processor. For external power
supply we are using
USB OTG option.

My questions are

1) is it possible to power up the board using USB OTG port? according
to OMAP3530 datasheet,
OMAP3530 requires 1A current, but through USB we can derive 500mA.But
in beagle_SRM_C4.doc,
topic : 5.5 HS USB 2.0 OTG Port, says
The USB OTG port can be used as the primary power source and
communication link for the
BeagleBoard and derives power from the PC over the USB cable. It is
possible to take this
to 1A by using a Y cable if additional power is needed.


2) how to calculate the power consumption ? any refernce?

Thanks and regards
N Reddy

OTG port is typically 100mA. A PC host can deliver up to 500mA. So, if the OTG port is configured as a client port and not OTG, then it could have access to up to 500mA. The OTG port does not provide any facility in itself to power the board. Whether it can power your board or not dependss on how you designed your board an what all is on it. The OTG port in Beagle can be used to power the board, but not all of the USB Host ports. So, yes it boots and runs, but you will not get full entitlement to all of its features. If you use a Y cable as clearly mentioned in the SRM, you can get up to 1A from a pair of USB host ports.

To calculate the current you look at each data sheet in your BOM, write down the typical current and add it all up for a typical number that would be close to your current requirements. But, it depends on overall speed you are running at and how much time you spend doing each function and which ones are running at the same time.

As you are basing you design off of the BeagleBoard, I suggest you take a few moment sand study the design and learn it. You can take measurements from it to give you some idea as to what you may be looking at in your design. At the end of the day, it is your board and only you can answer the current question.