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USB powered DM365?

Kevin Claycomb
Intellectual 420 points

I am a bit of a newb when it comes to USB enabled applications so hopefully someone can straighten me out.

I have done two custom DM365 designs, but neither utilized the USB controller.  In my new design I would like to power the entire board from the USB port.  That means that when I plug this new board into the USB port, the port must supply enough current to boot the DM365 part.  In my experience this process will take more (to boot all the way into linux) than the 100ma @5V that the USB spec says can be drawn out of the port before enumeration and switching to high power mode.  

It would seem like there has to be a way around this as many devices must draw more than 100ma on power up? 

Do I really have to enumerate before I can draw more than 100ma?  

Does the DM365 have any features designed to support this mode of operation?

I guess one spot it could be done would be in u-boot, right after reset before everything is spun up and you need lots of power.  Is that the right approach? 

I will have some sort of soft start on the power input to avoid large inrush currents.

Thanks for any guidance you can provide, I am hoping I am missing something fundamental that will make this problem a little easier.

Kevin

  • 0
    TI__Expert 7435 points

    Kevin,

    100ma@5V is as per USB spec.  Typically today's pc's do not restrict power (by default you get 500ms at 5V) (or the support for Green mode is not enabled in the BIOS).  In the future assume this mode to be supproted by default as PC's become more greener or customers start using the tablets instead of PC's.

    Coming to your question do you need USB just to power up the DM365 based product or would you also be using the USB port for other application purposes?

    If you need the USB port for power purpose alone then I would suggest you to write a configure the U-Boot with usb based serial support and enumerate for 500ma. In this way the PC will honor the enumeration during startup of your product and once Linux boots up your your device will enumerate as a serial device and full power will be kept on.

    On the other hand if you use the USB port for you application needs then you would have to write a custom usb app in both u-boot (minimal one) and linux (full app) environments.  You would have to creat a similar PC based host app to communicte with your DM365 based device.

    As I understand there are no default examples that are available as part of the DM365 package that demonstrate the sequence that you are looking for.  You would have to create your own.

    regards

    swami