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USB Hardware Connection to TMS320F28069

Albert Jansen
Prodigy 130 points
Other Parts Discussed in Thread: TMS320F28069

Hello,

I am in the process of designing a board that incorporates the USB functionality of the TMS320F28069. I am looking over the hardware specs and seeing that I need a pull up resistor on the device side to specify speed. I am wondering if the levels that USB uses for D+ and D- will be harmful to the controller? Should I use a level converter? Or just an isolator?

I am fairly sure that the levels will not be harmful, but I want to be 100% sure.

Thanks,

Albert

  • 0
    TI__Expert 8950 points
    Albert,

    The USB module on the F28069U has an internal pull-up. You don't need an external resistor.
  • 0 in reply to Adam Haun
    Prodigy 130 points

    Hi Adam,

    Thanks for the response. I am assuming this is true for all F28069F and M models as well? I am assuming I can configure the internal pullup in the software?

    Also, do you know if I need level translation on the D+ and D- lines?

    Thanks again,

    Albert

  • 0 in reply to Albert Jansen
    TI__Expert 8950 points
    Albert,

    Yes, the 2806xF and 2806xM also have USB. For a list of peripherals available on each part number, please see the Device Comparison table in the datasheet.

    You don't need level translation on the USB data lines. USB data is a 3.3V differential signal. The F2806x TRM has information on connecting the 5V VBUS line to the MCU.
  • 0 in reply to Adam Haun
    Prodigy 130 points
    Thanks a lot for your help. I was pretty sure, but didn't want to get the controller on the board and blow it up right away.
  • 0 in reply to Adam Haun
    Prodigy 40 points

    Hi，Adam-

    I've a similar question with the TMS320F28069U which was used as a self-powered full-speed device.

    USB 2.0 Spec require a 1.5kOhm resistor to pull-up the D+ to VCC 3.3V for full-speed device, while the TMS320F28069U datasheet and reference manual did not indicator if there's a internal pull up inside the MCU, as some other USB/Hub controller would specified in the datasheet, e.g. Cypress CY7C68013A or microchip USB2422.

    TMS320F280x Datasheet also didnot spefify the value of internal pull/up resistor (it give a current of around -140uA) , some reference explain that the pull-up is an active circuit but not passive resistor, processors.wiki.ti.com/.../General_Purpose_IO_(GPIO)_FAQ_for_C2000

    So the question is if I can use the internal pullup as the USB device insert detection and speed indentification for the Host, and disable it if neccessay because my device is self-powered?

     //Disable USB PHY
     GpioCtrlRegs.GPACTRL2.bit.USB0IOEN = 0;

     //Disable Pull-up of D+
     GpioCtrlRegs.GPAPUD.bit.GPIO26 = 1;

    Thanks and Best Regards

  • 0 in reply to Yeshan Ma
    TI__Expert 8950 points

    The 1.5k pull-up resistor is built into the internal USB PHY and is activated when the USB library sets the soft connect bit in the USB registers. The application software should monitor VBUS and make the appropriate call to the library when VBUS changes state.  There's no need to use the GPIO pull-up.

  • 0 in reply to Adam Haun
    Prodigy 40 points

    Hi, Adam-

    That's great that we don't have to made HW modification to add a resistor and transistor. The VBUS was already connected to a GPIO via resistor divider.

    And I've also noticed the SOFTCONN Bit in Chapter: 17.3.1.1.8 Connect/Disconnect.

    The datasheet and techinical reference manual were not quite friendly to new users.  :)

    Thanks for your information...

    Regards

    YS

  • 0 in reply to Yeshan Ma
    TI__Expert 8950 points
    Yeah, the documentation could be better. I'll put in a request to add some information.