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OPA2381 gain setting

Other Parts Discussed in Thread: OPA2381Hello,

I have been into at least a half dozen TI portals for tech support, FAE contact, etc., etc. to no avail. Maybe you can help.

I am using TI s OPA2381 specified for 135dB gain. Max info in data sheets is for Rf = 10 Meg ohm.

Can I increase gain, say to 160dB with Rf = 100 Megohm?

Please know that in the engineering climate today, it is important to have quick information from experts. Please don t make me drop TI from my clients component supply options for lack of technical support.

Len Cardillo
Vision1
Consulting
  • Hi Len,
    I have moved your thread to a better place.

    You are referring to 135dB gain, this sounds like the Aol gain to me. Which can't be changed.
    In the datasheet page 6, there are different gain figures for different Rf. Here the gain has been measured at 140dB with Rf=10MOhms.

    I'm not supporting this part particularly, but I think the TI support teams will be missing some key info to help you with consistency.
    For example:
    What does the signal at the input looks like?
    Which transient response behavior are you expecting?

    If you are not allowed to provide those information, then I suggest to try to simulate in your environment. OPA2381 model can be found on the product web page.

    Regards,
    -nico
  • Len,

    The short answer to your question is that you may NOT increase the gain of the OPA2381 above 140dB shown in the datasheet simply because at such high gain you hit against the AOL limitation (loop-gain) and the input noise becomes a dominant. In other words, any higher feedback resistor will result in the output being totally controlled by the input noise of the device instead of input current you are trying to measure.