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Analog switch for thermocouple

Martin Dusek11
Prodigy 180 points
Other Parts Discussed in Thread: TS3A4741

Hi, can you please recommend analog switch ic suitable for switching on and off 2 wires of thermocouple without distorting thermocouple's signal? The switch can have 2, 4, 8 or 16 channels and low rdson.

  • 0
    TI__Mastermind 45370 points

    Martin,

    If you have 2 wires to turn on and off I think you are looking for a 2-channel, 1:1 SPST switch.  I went to TI.com and used the signal switch selection tool to help narrow my search.  I used the filters on the left hand side to select 2 channel 1:1 SPST.  Then I clicked on the Ron parameter to sort the devices from lowest Ron to highest.  It looks like the TS3A4741 is the lowest Rdson switch we have in a 2-channel, 1:1 SPST configuration. 

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    Prodigy 180 points
    Hi Adam,
    thanks for your answer. Actually I have multichannel thermocouple device, so even 4, 8 or 16 are suitable for me.

    I searched TI's analog switches. As I'm not very experienced in this field and as e.g. TS3A4741 doesn't have sensor application or any relative application mentioned in Applications part of the datasheet I have doubts whether the switch won't distort thermocouples low signal somehow (e.g. by adding even small voltage offset). Can you confirm that these devices are suitable for switching analog signal of (quite precise) measurement device? The signal will go from thermocouple through the switch to A/D converter.

    Thanks
  • 0 in reply to Martin Dusek11
    TI__Mastermind 45370 points

    Martin,

    Our signal switches are simple bi-directional passive FET switches.  They do not have any internal buffers on the signal path and will simply pass what ever signal is places on the drain to the source with little effect to the signal.  Ideally these switches would be modeled with 0 ohm wires but of course there are some paracitics to be mindful of in practice. 

    The main parameters to pay attention to for signal integrity are the Rdson, Ron flatness, input capacitance, charge injection, THD, etc.  You may filter our products by all of these parameters in the signal switch search tool on ti.com by selecting the parameter from the left hand side filters.  

    The first 4 pages of the analog switch guide are helpful explaining how the parameters effect your signal.  Also the application note Understanding and interpreting standard liner and logic datasheet has a lot of good information as well. 

    I hope this helps explain that most of our passive FET switches will be suitable for your application and shows you how to evaluate the differences between the performance of our product.

    Let me know if you have additional questions,

    Adam