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OPA836: What is the possible gain range for this amplifier?

Part Number: OPA836
Other Parts Discussed in Thread: OPA838, , OPA847

Hello,

I would like to know the possible gain range for OPA836 & OPA838 amplifiers?

Regards,

Jadhav

  • Hello Jadhav,

    The OPA836 gain and attenuation settings can be found in tables 3 and 4 of the datasheet. You can see a picture of these below:

     The OPA838 is a decompensated amplifier, and needs a minimum gain of 6 V/V for proper functionality. You will see in tables 1 and 2 of this datasheet recommended resistor values that go up to gains of 20 V/V, however the amplifier gain can be still increased further. The limitations here will be a result of the input/output voltage ranges, resistor noise and device stability rather than a "max gain" of the device. I would recommend running simulations and seeing the device functionality at the gain you are trying to achieve. 

    Best,

    Hasan Babiker

  • The gain range for VFA op amps like these can be quite wide but that gain will interact with frequency response. Really can only answer in the context of desired signal processing needs in terms of Bandwidth, DC precision etc. The reply below with the internal fixed resistors is one package option for the OPA836. I think your question was assuming external R's. Also, there are external options to use a de-comp part like the OPA838 at low or even attenuating gains if need be. That is discussed in the OPA847 data sheet on page 12. Also, there will be an EDN re-issue of the original 1997 article on this shortly posting up.

    www.ti.com/.../opa847.pdf

    Assuming there is a bandwidth constraint, then the next step would be to find the max gain before you drop below that bandwidth. Oddly, while most folks work with the gain bandwidth product idea, that actually only applies for a 90deg phase margin. A recent post I put up on planet analog talks a little about the bandwidth extension you get at lower phase margins - or you can use the PDS plots vs gain to estimate max gain. Eventually, you should take your design into TINA to assess SSBW and then check for slew rate limits as well.

    www.planetanalog.com/author.asp