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LME49990

Gerhard Kreuzer
Expert 2600 points
Other Parts Discussed in Thread: LME49990, THS4131, OPA827

Hi,

can anybody tell me the imput impedanz of the LME49990, want to use it as elektrometer/non inverting amp. Thanks a lot.

 

With best regards

 

Gerhard

  • 0
    TI__Expert 3840 points

    Hi Gerhard,

    I am looking into this for you and will provide information as soon as I have it.

    Thanks and Best Regards,

    JD

  • 0 in reply to John De Celles
    TI__Expert 3840 points

    Hi Gerhard,

    The common-mode impedance is in the hundreds of Mohms while the differential mode is around 10 Mohms. 

    Best Regards,

    JD

  • 0 in reply to John De Celles
    Expert 2600 points

    Hi John,

     

    thanks.

    One more question. I need a differential circuit, so I take two LMP49990, because noise is an issue. I found out by simulation, that I need a relatively small resistor from + input to fround. Why? I use the amplifiers as non inverting amps with gain 100. The outputs go to an THS4131 for further processing, filtering and ends up in a sigma delta ADC (24 Bit) which also offers true differential signal path.

    This resistor bring down my input impedanz which should be about 1M ....

    Now I tried OPA827, which is recommended for high impedanz sources, because its current noise is low.

     

    Did you have another idea to do the job?

     

    With best regards

     

    Gerhard