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AM3354: USB interface without VBUS

David Park
Expert 6650 points
Part Number: AM3354

Hi,

Customer would like to use USB0 with device mode and USB1 with host mode.

There are 2 questions.

1. How can it connected when use USB0 without VBUS from PC?

it will use only D+, D- and GND.

could you check below connection?

VBUS is floating and there is no pull up on D+

2. USB1 for host mode

USB1 is connected to LTE module and LTE module USB_VBUS is 1.8V.

Is USB available with only D+, D- connection to LTE module without 4.4V for USB1_VBUS?

or for host mode, is 4.4V mandatory on USB1_VBUS?

Thanks.

  • 0
    TI__Guru**** 168181 points

    Hi David,

    David Park said:
    1. How can it connected when use USB0 without VBUS from PC?

    This doesn't comply with USB Specification. VBUS is mandatory. AM335x USB controller doesn't function without USBx_VBUS pin connected, in both host and device modes.

    David Park said:
    USB1 is connected to LTE module and LTE module USB_VBUS is 1.8V.

    You would have to convert the VBUS to 5V for USB1_VBUS pin.

    David Park said:
    Is USB available with only D+, D- connection to LTE module without 4.4V for USB1_VBUS?

    No. See my answer for your question #1 above.

    David Park said:
    or for host mode, is 4.4V mandatory on USB1_VBUS?

    Yes.

  • 0 in reply to Bin Liu
    Prodigy 190 points

    Dear Bin,

    I can't exactly understand the highlighted sentence in your TRM document.

    It means that if AM3354 is the device mode and USB is self-powered, I think voltage on AM3354 VBUS pin don't need to be sourced by host, right?

    please, check whether the below block diagram is possible to interface USB0(Device mode), USB1(Host mode)?

    - USB0_VBUS on AM3354 is sourced by DC/DC 5V on our board and VBUS is not used from usb connector(from PC)

    - USB1_VBUS on AM3354 is sourced by DC/DC 5V on our board and VBUS on LTE module is sourced by DCDC 1.8V on our board.

  • 0 in reply to Kwangbog Ham14
    TI__Guru**** 168181 points

    Hi Kwangbog,

    Are these follow-up questions to the same project as David Park mentioned in his first post?

  • 0 in reply to Bin Liu
    Prodigy 190 points

    Dear Bin,

    I am hardware engineer and it's same project.

    The main purpose what i want to know is that it's possible to communicate AM3354 with PC through USB0 interface(Only with D+,D- signal) without VBUS0_VBUS on AM3354.

    Q1. As the mentioned on your TRM, let me know what's the meaning of the below sentence?

    "Note that both USBs are self-powered and the device does not rely on the voltage on the VBUS line
    sourced by an external host for controller operation when assuming the role of a device."

    Q2. Please, check the second block diagram whether is it possible or not.

    - USB0_VBUS on AM3354 is sourced by DC/DC 5V on our board and VBUS is not used from usb connector(from PC)

    - USB1_VBUS on AM3354 is sourced by DC/DC 5V on our board and VBUS on LTE module is sourced by DCDC 1.8V on our board.

    Best and Regards,

    Kwangbog HAM