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Original question:

RE: ADS114S08: Thermocouple and RTD signal transmitter Design Question

TS5A26542: Effect on uV analog signal

Mahmoud Zannerni62
Intellectual 655 points
Part Number: TS5A26542
Other Parts Discussed in Thread: ADS114S08, TMUX1119, TMUX1108, TMUX1109

Hello,

I am designing an instrumentation circuit with ADS114s08, and I am planning to use TS5A26542 switch for the following purposes:

1. Routing thermocouple signal through the switch, it is in uV.

2. Routing RTD excitation current through the switch to use the same current source for many RTDs.

3. Using the switch to connect a different value of the bias resistor in RTD measurement.

 

Will this downgrade my measurement accuracy? and will it behave exactly as a mechanical relay if I assume the relay has the same on resistance?

 

Regards,

Mahmoud

  • 0
    TI__Expert 3900 points

    Hi Mahmoud,

    The TS5A26542 can work in your system for these applications. The switch will behave similar to a relay but has parasitics  associated with the construction of the CMOS switch.

    One particular parameter to pay attention to in this case is the on/off state leakage currents. The TS5A26542 has decent leakage performance but is around 100nA in the 85°C range. The leakage current can cause an error based on the level of the input impedance in your system coming from one of your temperature sensing devices.  Here is a LINK to a TI precision labs training on this topic.

    If you are trying to resolve a uV level signal I would recommend looking into TI's precision mux's that have ultra-low leakage currents. This is the TMUX11xx family for low voltage muxs. Such as the TMUX1108, TMUX1109, or TMUX1119.