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USB Question

Ali Movahedi
Intellectual 840 points
Other Parts Discussed in Thread: AM3517, MSP430F5528, TS3USB30, TS3USB221

Hello,

Due to the nature of my design I am interfacing the MSP430F5528 to the AM3517.  Can I connect both USB lineof MSP430F5528 and the AM3517 OTG (USB0_VBUS, USB0_DP, USB0_DM and USB0_ID) together and having  it externally available as a one set DP, DM, GND and the VBUS.  When the PC is interfaced through USB with the unit by software to decide which processor to communicate to the host (MSP430F5528 or AM3517).   My thought was that to enable one USB port at a time and disable the other.  This is possible for the MSP430F5528 since its USB data lines are multiplex with the I/O lines but I am not sure if this is true in regard to AM3517.

 

Thank you,

Ali.

 

  • 0
    TI__Guru 63145 points

    USB devices are connected with controlled impedance transmission lines which are required to prevent signal integrity issues.  Connecting two devices together on the same USB port will result in major signal integrity issues caused by transmission line stubs.  This is not recommended.

     

    Regards,

    Paul

  • 0 in reply to peaves
    Intellectual 840 points

    Hi Paul,

     Thank you for your prompt response.  Let me elaborete a bit more if I may.

    According to Ajay in reference to ,

    http://e2e.ti.com/support/dsp/sitara_arm174_microprocessors/f/416/t/91317.aspx

    one can disable the USB port on the AM3517. If so then PC can communicate with MSP430F5528 freely. This is true also when the USB on the MSP430F5528 is disable and PC can communicate with the AM3517 freely as well.

    If this is still an issue then how one would go about it. I only can have one port available outside of my unit but I need to communicate to both USB ports independently .

     

    High Regards,

    Ali

  • 0 in reply to Ali Movahedi
    TI__Genius 14545 points

    Ali,

      You might be interested in TS3USB30 to complete this job. USB (High Speed) is very sensitive to stubs / transmission line reflections.

    If you have only one external USB interface, a switch like the above or one of these would allow you to talk to both devices independently while eliminating any signal corruption between the two interfaces.

  • 0 in reply to dabuan
    TI__Guru 63145 points

    Some high speed PHYs may not operate as expected with the additional parasitic capacitance and resistance of the TS3USB30 device.

     

    For example, I have been told one of our internal USB PHYs may have problems operating with the USB specified limits if more than 3 ohms of series resistance were added to the USB signals.  The TS3USB30 has a maximum on resistance of 10 ohms.

     

    The TS3USB30 also has 7pf of shunt capacitance which may also cause a problem.

     

    I still stick to my original comment. This is not recommended.

     

     

    Regards,

    Paul

  • 0 in reply to peaves
    Intellectual 840 points

    Hi Paul,

    Please let me know what you think about the TS3USB221.  This switch has lower Ron than TS3USB30.  Here are the feature ofTS3USB221,

    Features

     

    • VCC Operation at 2.5 V and 3.3 V
    • VI/O Accepts Signals up to 5.5 V
    • 1.8-V Compatible Control-Pin Inputs
    • Low-Power Mode When OE Is Disabled (1 µA)
    • rON = 6 Maximum
    • rON = 0.2 Typical
    • Cio(on) = 6 pF Maximum
    • Low Power Consumption (30 µA Maximum)
    • ESD > 2000-V Human-Body Model (HBM)
    • High Bandwidth (1.1 GHz Typical)
    • APPLICATIONS
      • Routes Signals for USB 1.0, 1.1, and 2.0
      • Mobile Industry Processor Interface (MIPI) Signal Routing

     

    If this part is not the suitable for this application then what would be the use of the TS3USB221 please?
     
    High Regards,
    Ali.
  • 0 in reply to Ali Movahedi
    TI__Intellectual 2470 points

    Ali,

    I wanted to know what mode you are planning to use USB on AM35xx? Is it Full Speed, High Speed or Low Speed?

  • 0 in reply to Ali Movahedi
    TI__Intellectual 1465 points

    Hi, Ali,

    If Ron and Con are of a concern, I do recommend TS3USB221 over TS3USB30. The 221 has about 3.5ohms Ron typical and 5pf Con typical and this is as low as you could find on the market right now.

    We have a lot of mobile device customers using this device to do similar application as yours. (interfacing between standard USB host and USB OTG).

    Thanks,
    David 

  • 0 in reply to Varun Shah
    Intellectual 840 points

     

    Hi Varun,

     

    May be in case of AM3517 in high speed and in case of MSP430F5528 if not possible to run in high speed then run it in  full Speed mode.  What I understand the the TS3USB221 can run up to 480mbps then it should not be an issue running it in high speed.

    Thanks,

    Ali.