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Original question:

MUX508: MUX508 to replace ADG508F.

MUX509: What is the common mode voltage range for the input of MUX509

user3932123
Prodigy 110 points
Part Number: MUX509

Hi ,

I want a little confused about the usage of MUX509. When the input source is float like TC or ultrasonic transducers, can MUX509 work with just postive 12V power?

I see the input range is VSS to VDD. But for these signal source, they don't have dc voltage relative to the system ground. Maybe there is a bias voltage after the chip(On the D pin), But s pin is still float.

  • 0
    TI__Intellectual 2165 points

    Hi user3932123 , 

    If you want to use single supply of VDD=12V, the VSS should be connected to ground.

    As indicated in the datasheet recommended operating conditions, the source voltage can be within the range of VSS~VDD( 0~12V with a 12V power supply). 

    As long as the Vs voltage doesn't exceed the recommended operating condition range it's fine. 

    thanks,

    Helen

  • 0 in reply to Helen Sun
    Prodigy 110 points

    Hi, 

    I think maybe use don't get my point. Whey using +12V and 0V to the VDD and VSS I think it is OK for most of time. But for some inputs like TC(thermocouple), it is always differential and not referenced to the ground of this Mux. How keep the input voltage inside the range of this chip? Thanks.

  • 0 in reply to user3932123
    TI__Intellectual 2165 points

    HI user3932123, 

    The VDD/VSS range for input pin is specified referencing to the GND pin( same ground as the power supply). 

    If you have a differential input, the inputs still need to be within the power supply range referencing to the GND pin. 

    Thanks,

    Helen

  • 0 in reply to Helen Sun
    Prodigy 110 points

    Hi Helen,

    Thanks for your feedback. What is the typical method for using MUX509  to connect with thermocouple(TC temperature sensor)? Should I add the reference to all the thermocouple inputs? Can the reference dc bias voltage be added at the D pin of this chip?

    When power the MUX509 with positive and negative voltage, should the differential input still need to be dc biased? 

  • 0 in reply to user3932123
    TI__Mastermind 45340 points

    user3932123, 

    The MUX509 is a passive FET switch and doesn't need any bias voltage to operate.  This device can't source or sink current.  The only way signals pass through this device is based off external source and loads connect to the I/O pins. 

    You can add a DC bias to the D pin of the MUX509 as long as the voltage is within the recommended operating conditions of the device Vss to Vdd.  

    Do you have a diagram of how you want to connect the MUX509 to your thermocouple with the voltages labeled  so I can see if it helps me understand your question? 

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    Prodigy 110 points

    Hi, I want to use the TC input in float mode. So it means that to S1A and S1B there is no DC votage. It this method can work? MUX509 is single powered with 12V. 

    Does all TI Mux can votage in this mode? I mean how to judge a switch is passive? Thanks.

  • 0 in reply to user3932123
    TI__Mastermind 45340 points

    user3932123, 

    You can tell if a switch is passive or not by checking if there is a Voh (output voltage) or Ioh (output current) specification in the datasheet.  You will notice that almost all of the switches on the analog switches section of Ti.com are passive.

    I don't know what TC voltage ranges you have but with MUX509 supply voltage = 12 V you can support voltages from 0 V to 12 V on the S and D pins.

    Thank you,

    Adam