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AM335x USB

shekhar SAINI97194
Intellectual 550 points

AM335x as USB Device

The usb 5V is connected to PMIC, which will generated the power for AM335x but before that USB data and VBUS of AM3335x is already powered as they are connected directly to host.

What would happen if we connect external USB host to AM335x and the system (AM335x) is not powered.

  • 0
    TI__Guru 62945 points

    The USB host will source 5 volts to the VBUS signal before the USB device is attached, but it should not be sourcing the DP/DM signals.

    The VBUS inputs would have a potential applied before the PMIC powers up the AM335x power supplies, but this does not cause a problem because the two VBUS inputs are fail-safe.  Fail-safe inputs allow a voltage potential to be applied before power is applied to their respective power supply terminals. 

    The USB host will have 15K ohm pull-down resistors on both DP and DM signals waiting for the attached USB device to turn on a 1.5K ohm pull-up connected to the DM signal to indicate it is a low speed device or turns on a 1.5K ohm pull-up connected the DP signal to indicate it is a full/high speed device.

    Regards,
    Paul