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what can the VBUS pin do?

YJ Liu
Expert 1675 points

host is MUSB on DM355.

when I connect a 4.8V to VBUS(should not lower than 4.9V), it report VBUS_ERR.

However, when I only use HOST mode , my device can operate in 4.8V, but I need a charge pump power IC to ensure the 5V supply(that will increase my device cost),so the VBUS_ERR will not appear.

So , can i disable the error? and not connect VBUS?

thanks.

  • 0
    TI__Expert 5475 points

    Hi,

    I think there is something wrong going on your system or board.

    The controller requires a 4.4V Voltage on the VBUS Line for the comparator to report a good operating voltage. However, due to voltage drop between source and target, it is best that you supply a minimum of 4.7V etc to account for the Loss, assuming that the target behaves properly and does not sink much current.

    Having said that, as a Host since there could be bus powered device connected to the host controller, the host is required to furnish the minimum amount of voltage and current on the VBUS line. For this reason, the controller insures that this resource is available. If this resource is not available after it attempts to furnish it by driving USB_DRVVBUS high, it will generate an error and close the session.

    I do not think a capability exists to override this feature. The only time we build this capability is when we do not bond out the VBUS pin. If VBUS pin is bonded out there is no valid reason to disable this capability.

    In summary, make sure you have designed your power source to source enough voltage and current as well as ensure that the target is a compliant device.

    Best regards, Zegeye