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DM357 USB Overcurrent handling

Matt C
Prodigy 180 points


The DM357 Eval kit from Spectrum has USB OTG and a USB power distribution switch, but it looks like the overcurrent pin on the power distribution switch goes to CPLD input pin 84, and then is sent out via CPLD output pin 98 to header JP1 and unused.  I.e., the DM357 eval board does not do anything with the overcurrent signal.

We are using Monta Vista Linux on the DM357.

Question...  How can overcurrent conditions supported by the DM357?

In software?  If so, does the driver support this?  What pin should the overcurrent signal be connected to?

In hardware (CPLD)?

 

Thanks

  • 0
    TI__Mastermind 41665 points

    Matt C said:
    Question...  How can overcurrent conditions supported by the DM357?

    As you suggest it looks like the overcurrent pin from the power supply is not being used, so the DM357 does not inherently detect an overcurrent condition from the power supply directly, however it will detect if the 5v VBUS signal on the USB interface goes below spec, the USB hardware on the DM357 has a voltage sensing input for this purpose.

    Matt C said:
    In software?  If so, does the driver support this?

    I do not believe the drivers as is support using the overcurrent signal from the power supply, they will however detect a drop in the VBUS voltage (you tend to get VBUS errors on your terminal from the driver if you try to plug a device that is drawing too much current into the USB connector).

    Matt C said:
    What pin should the overcurrent signal be connected to?

    If you wanted to use the power supply signal for overcurrent you would connect it to an interrupt line on the processor, most any available interrupt line would do though you would have to configure the software to handle that particular interrupt.