This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

OPA211: Inverting application of OPA211 failure

Part Number: OPA211
Other Parts Discussed in Thread: OPA365

The output of OPA211 is wrong when simulation with Pspice.

While replace it with OPA365,the result is right.

  • Hi Eric,

    You missed the input Vcm requirements for OPA211. The V+ node is 0.227V and V4 generator needs DC biased at 2.5V. Please try the following. 

    I configured 2.5V at V+ with 200||2kohm, and DC biased the generator at 2.5V with 100mV riding on top of it. I think that you are doing square wave at 50kHz, see the attached simulation.

    /cfs-file/__key/communityserver-discussions-components-files/14/OPA211-12182020.TSC

    If you have additional questions, please let us know. 

    Best,

    Raymond

  • Thanks, Raymond

    Your reply resolved my issue.I have another questions.

    1, My circuit is used in current measure of the inverter's low-side phase leg.

    The accuracy of current sampling is very high (0.1% or higher).

    Whta is the best topology?

    I want use OPA365 to replace OPA211.

    2, I want to know  the difference between two discret Op amps and integrated Op amp.

    For example,two OPA211 and one OPA2211,regardless of prices.

  • Hi Eric,

    1, My circuit is used in current measure of the inverter's low-side phase leg. The accuracy of current sampling is very high (0.1% or higher). What is the best topology?

    Please take a look at the following threads. 

    https://e2e.ti.com/support/amplifiers/f/14/t/704915

    https://www.ti.com/lit/ug/tidu474/tidu474.pdf?ts=1608163465227&ref_url=https%253A%252F%252Fwww.ti.com%252Ftool%252FTIDM-3PHMETER-ROGOWSKI

    https://e2e.ti.com/support/amplifiers/f/14/t/891120

    https://e2e.ti.com/support/amplifiers/f/14/t/818894

    From the diagram you presented, it will be the best to one of the techniques above. For AC application, AC current transformer is used, but if you want to have the better than 0.1% accuracy, may be current sensing method should be used. If you want a very high precision, then instrumentation amplifier may be used. Here are the issues.

    If the application is high AC voltage 3-phase current measurement, then the current transformer will be likely the best options for the current measurement. You can make or buy current transformer on the market,  if you do not want to use Rogowski coil method (It is same working principle, but different package types). 

    You have location 2 and 3 in Rshunt resistance, it is likely that the resistances are very low. In order to measure the current accurately, you will consider differential input measurement. Since this is AC current measurement, you probably want to maintain the measurement accuracy in the entire current ranges (low to high that is < 0.1% errors). In addition, Rshunt values are likely small, your output current circuit will require some gains. 

     If location 2 is connected to neutral and tied to ground (depending on application), you may use an op amp circuit you are working with. If max. current per each phase is operating at 1Arms, <0.1% will be <1mArms. It may be difficult to achieve the accuracy, since the ground noise will be higher than that. If each phase is operated at 10Arms, then it may be doable. But the differential sensing method is still superior than single ended current measurements. 

    2. I want to know  the difference between two discrete Op amps and integrated Op amp.  two OPA211 and one OPA2211

    There should not be big differences between dual or single package op amp, e.g. OPA211 vs. OPA2211 (it is same circuit design). Please pay attention to thermal information of different package types in thermal resistance presented in section 6.4 and 6.5 of the datasheet. You may want to select lower degreeC/W package for your application.

    If you have other questions, please let us know. 

    Best,

    Raymond