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USB interface

GeoD
Intellectual 325 points
Other Parts Discussed in Thread: AM3358, TPS2041, TPS2041B

Hello,

In the EVM AM3358 baseboard schematics the USB0_DRVNBUS is used to control VBUS of the processor and this processor VBUS connects to the VBUS pin of the USB connector.

I want to use the processor in USB host self powered mode and in additon to use a 4 port hub device. I am using the downstream ports of the hub device to detect an overload condition (hub provides an overload pin and will report it to the host when occurs and this pin connects to a TI TPS2041 device. The output of this device (controlled from hub) enables the power to the external device (based on the OVR condition). So, in this case the hub device provides the power for the VBUS pin for the USB connector.

In this hub case I described above how the USB0_DRVNBUS signals and VBUS power signals of the processor are used and connect so I have a USB self powered host?

Thanks,

Yu-Li

  • 0
    TI__Guru**** 393215 points
    Hi Yu-Li,
     
    Please check AM335X Technical Reference Manual sections 16.3.1 and 16.3.7. My conclusion from reading these two sections is that in your case both USB0_DRVVBUS and USB0_VBUS can be left not connected, and you have the option of selecting host mode either by tying USB0_ID to GND or leaving it unconnected and selecting host mode through software.
  • 0 in reply to Biser Gatchev-XID
    TI__Mastermind 27890 points

    It is important to understand that while in host mode, AM335x must control VBUS power delivery to downstream ports via the relevant DRVVBUS pin. After asserting DRVVBUS, the controller will expect to see a valid VBUS on USBn_VBUS within 100ms or it will assume that an OC condition exists and will disable the interface.

    Both DRVVBUS and USBn_VBUS must be connected if host functionality is desired.

  • 0 in reply to -DK-
    Intellectual 325 points

    Hello,

    I am a bit confused  after this response. All I want to do is having the processor in a host self powered mode and have a USB 4 port hub. My hub is the CY7C65632-48AXCT device. In the downstream side I am using the _OVR# and _PWR pins of this hub (PWR pin connects to the Enable pin of a TPS2041B device) and the OUT pin of the TPS2041B is the power I am using for the VBUS pin of the USB connector.

    I am still unsure how to use the processor's DRVVBUS and USBn_VBUS with my USB hub.

    Can you please help?

    Thank you,

    Yu-Li

  • 0 in reply to GeoD
    TI__Mastermind 27890 points

    Yu-Li,

    For your application  you will need to a switching mechanism (a simple FET switch would do) of some sort for VBUS of the AM335x port that is to be connected to the upstream port of your hub. I understand that the hub is not a removable device in your design, but because the USB controller in AM335x was designed as an OTG controller, it must control VBUS via DRVVBUS for its downstream ports.