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TS3USB3000 Signal Termination

Jared Becker
Genius 11845 points
Other Parts Discussed in Thread: TS3USB3000

Hi Team,

When the TS3USB3000 switches from one channel to the other, I would like to understand the behavior of the path that is no longer connected to the output. My main concern is signal reflection..

Lets say that I am driving a signal into the USB +/- pins with the output at the D+/- pins, then I flip my switch so that I am driving a signal into the MHL+/- pins with the output at the D+/- pins. The signal that is being driven into the USB+/- pins is still being driven into the pins but is no longer connected to the output (D+/- pins), thus I am not sure what will happen to the signal at that point.. Is there some sort of internal termination, or will I get signal reflection?

For instance, the DS10CP152Q is a switch that contains output termination to minimize insertion and return losses, does the TS3USB3000 have something similar?

Thank you,

Jared

  • 0
    TI__Mastermind 45575 points

    Jared,

    When a TS3USB3000 signal path is not conducting (switched off) the device goes into a high impedance state Hi-Z.  You can see this parameter characterized in the datasheet by the off state leakage current (DC) and the off isolation (AC).  You can look at this thread below for more information on how to calculate the Hi-Z of a switch in its off state.

     

    This post has some S-parameter models of this device when it is conducting but not when the switch is off.  What is it in your system that you are worried about reflections from the TS3USB3000 when the switch is off? 

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    TI__Genius 11845 points
    Hi Adam,

    I am worried about EMI that gets produced from the non-terminated transmission line.

    If I understand correctly, there is no termination within the device, thus I can expect signal reflections when using the switch with two inputs on the USB/MHL side. If there is only one input on the D+/- side, then this is not a concern.

    Please let me know if I am misunderstand anything.

    Thank you,
    Jared
  • 0 in reply to Jared Becker
    TI__Mastermind 45575 points
    Jared,

    Yes, if you are driving a signal into the signal path that is not selected you will have reflections due to the hi-Z state when the switch is off or not selected.

    Thank you,
    Adam