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USB power supply problem for OMAP3530

babu reddy
Intellectual 580 points
Other Parts Discussed in Thread: OMAP3530

hi all
 
we are working on devkit8000, OMAP3530.
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.

PLEASE CLARIFY THIS DOUBT?
WETHER WE NEED TO USE Y-CABLE FOR USB POWER SUPPLY OR NORMAL SINGLE CABLE IS ENOUGH?

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

Thanks and regards
N Reddy

  • 0
    TI__Guru 62975 points

    I am not familiar with the devkit8000.  So I’m not able to answer your specific questions related to it.

    I will try to answer your question about using two USB ports to get a 1A power source.

    The USB specification requires a standard high-powered USB host port to provide a minimum of 500mA at 4.75 – 5.25 volts.  The port may source more than 500mA but must not source more than 5.0A.  So you should not plan on it sourcing more than 500mA.

    There is no requirement for a USB host to use the same voltage supply to source power to multiple USB ports.  So the voltage sourced to each USB port may be different.  This may cause a problem if you connect two voltage supplies together with the Y-cable.  Even if the two ports are sourced from the same power supply a small difference in resistance of the two current paths may prevent equal current sharing between the two ports.

    This may work, but is not a good design practice.  There is some risk of damaging the USB host or other components if the two ports are not sourced from the same voltage supply.

     

    Regards,
    Paul