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Bus-Switch Characteristics

AP
Intellectual 370 points

Hello,
Bus-Switch Application: Save bidirectional FPGA I/O pins from too high or too low negative voltages coming from the I/O interface.
The Digital Bus Switch Decision Tree in the Digital Bus Switch Selection Guide claims that all listed bus-switch families will clamp undershoots at -0.5V when the switch is on. Is this really true? I thouhgt only the CBTS family has such a feature? Or will the CBTS family already start clamping at -0.3V and all others at -0.5V?
Mind: I don't care about undershoot things when the switch is Off. In the application, the switch will always be On. Thanks

  • 0
    TI__Mastermind 46480 points

    All of the switches will have a clamp diode to gnd. The problem with switches is that if you go much below gnd the switch will turn on. (Connect input to output)

     We have switches with a C-rev at the end that can prevent turn on. 

      Buffers would be best for cleaning up overshoot and undershoot.

  • 0 in reply to Chris Cockrill
    Intellectual 370 points

    regarding buffers: I would need auto-direction mode, and it seems that these ones are not able to drive some mA and so they don't seem suitable for an I/O interface (card edge). That's why I'm looking at the bus-switches. I think I will spend some extra TVS devices against undershoots along with a bus-switch.