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TMUX7234: TMUX7234 and THVD4431

Rob
Prodigy 110 points
Part Number: TMUX7234
Other Parts Discussed in Thread: THVD4431,

Tool/software:

Hello,

I am using a THVD4431 to get RS-232 or RS-485 or RS-422 signals. As the DB9 connector wiring is different (for my equipments) for each protocol. I would like to redirect the signals on the DB9 connector depending on the selected mode. I am thinking of using TMUX7234 between the THVD4431 and the DB9 connector.

1. Does this implementation seem correct to you?

Here is a schematic diagram:

Note: "Sx" (S1, S2, S3...) represents a TMUX7234.

2. In some configurations, the "Dx", "SxA" and "SxB" pins are floating. Will this be a problem?

Thanks in advance for your help.

  • 0
    Prodigy 110 points

    I will power the TMUX7234 with VDD = +15V and VSS = -15V.

  • +1 in reply to Rob
    TI__Genius 9805 points

    Hello Rob,

    How many signal paths are you are trying to mux between? 

    The implementation seems right, no issue with the pins floating. 

    Thanks,

    Nir 

  • 0 in reply to Nir Gilgur
    Prodigy 110 points

    Thank you for your answer.

    Being able to leave the TMUX7234 pins floating in certain conditions reassures me.

    I use several TMUX7234 in cascade and for each of the signals (RS-232, RS-485 and RS-422) because the pinout used in my equipments is different for each protocol. I want to use only one DB9 connector for these 3 protocols.
    8 wires are therefore connected from the THVD4431 to the DB9 connector in RS-232 mode. 2 wires are connected from the THVD4431 to the DB9 connector in RS-485 mode. 4 wires are connected from the THVD4431 to the DB9 connector in RS-422 mode.

    Here is an illustration:

    Do I need to make impedance adaptations between a THVD4431 and a TMUX7234, between two TMUX7234, between a TMUX7234 and a DB9 connector?

  • 0 in reply to Rob
    TI__Genius 9805 points

    Hello Rob,

    Yes, you will need impedance matching to remove undesired behavior and reflections on the signal path. 

    Each TMUX7234 has an internal resistance (Ron) that might cause impedance mismatch that needs to be accounted for.

    Thanks,

    Nir 

  • 0 in reply to Nir Gilgur
    Prodigy 110 points

    Ok, thanks. How can I match the impedance between ICs?

  • +1 in reply to Rob
    TI__Genius 9805 points

    Hello Rob,

    Impedance matching is achieved when the source resistance is equal to the load resistance. Since our analog muxes are passive devices, we do not have an input or output impedance of the Sx pins and Dx pins. For the TMUX7234, we do have an Ron, which is 3.5Ω(typ), which will be the effective resistance that you will see from S to D on your signal when the switch is on.

    Thanks,

    Nir 

  • 0 in reply to Nir Gilgur
    Prodigy 110 points

    Ok, thanks for your help.

  • 0 in reply to Nir Gilgur
    Prodigy 110 points

    Hello,

    Can I apply voltages if the TMUX7234 is powered off?

    I will have signals that will be applied to the source or drain pins after the power supply is turned off.

    I don't risk damaging the chip?

  • 0 in reply to Rob
    TI__Genius 9805 points

    Hello Rob,

    The TMUX7234 doesn't have powered off protection. Meaning applying a voltage on the source and drain pins with the supply turned off might damage the device. If this is an important part of your design and it can't be altered, I might be able to recommend a different device.

    What are some critical parameters you are looking for in a multiplexer for your application? It will help to narrow down the right device.

    Thanks,

    Nir