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OPA1656: OPA1656

Farzaneh Faridi
Intellectual 595 points
Part Number: OPA1656
Other Parts Discussed in Thread: OPA192, , OPA551, OPA547, OPA593

Dear members:

For a measuring circuit I need an operational with output current of 100mA and differencial supply voltage of 15V.  I want to make a Howland current pump at the first stage and then another stage for measuring. First I made the circuit with OPA192 as you can see below:

I need to have 75mA on the load resister here (40R). I made a DC sweep simulation and you can see that it works perfectly. 

the problem is that, OPA192 MAC output current is 65mA and it doesn't work for a current value above it. I was searching for another chip and I found OPA1656. Looking at the datasheet it should be working for my purpose. I downloaded the pspice model but it doesn't work as I expected. keeping the circuit as it was and change the operational to OPA1656 this is the simulation result:


Any suggestion would be greatly appreciated.

Farzaneh

  • 0
    TI__Guru* 93105 points

    Hello Farzaneh,

    A 100 mA output current requirement is best handled by a power operational amplifier, rated for high output current and having a package designed for higher power dissipation. Here are some precision power op amps to consider for the Improved Howland Current Pump application:

    OPA551 - https://www.ti.com/product/OPA551

    OPA547 - https://www.ti.com/product/OPA547

    OPA593 - https://www.ti.com/product/OPA593

    Let me know if you have any questions.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    Intellectual 595 points

    Hi Thomas,

    Thanks for your kind response. I checked the OPA551 basically because it's cheaper than the other ones. I downloaded the pspice model, but it seems that it's not working.

    Any suggestion?

    Farzaneh

  • 0 in reply to Farzaneh Faridi
    TI__Guru* 93105 points

    Hello Farzaneh,

    I'm having problems too attempting to apply the OPA551 model in TI's PSpice for TI simulator. The Model development team has been working on the power op amp models and may have inadvertently created a problem with the OPA551 model. I'm going to ask our local modeling engineer to test the OPA551 model and see if he too has problems with it. Please give us a little time to look into the issue.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • +1 in reply to Thomas Kuehl
    TI__Guru* 93105 points

    Hello Farzaneh,

    I spent time reviewing the OPA551 PSpice model using Pspice for TI. I had set up a basic non-inverting amplifier circuit from scratch and it wouldn't initially run. Pspice for TI was telling me I had a connection error. We found the problem was the way I was making connection to Flag pin. I had come in from the side of the pin with a resistor to ground. It didn't like that orientation. The connection problem was solved by making the resistor connection downward from the pin to ground as can be seen in the image below. The error ceased and I was able to run different simulations with the OPA551 model.

    The Model engineer showed me an OPA551 model test circuit that can be accessed from within Pspice for TI. That is the image seen below. I ran a transient analysis using it and the is the other image. Therefore, the OPA551 model looks to be working okay. I suggest you look for whatever else may be preventing it from working in your circuit from simulating.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    Intellectual 595 points

    Dear Thomas,

    I could get the appropriate result in simulation. Thanks a lot for your time dedicating. 

    Farzaneh

  • 0 in reply to Farzaneh Faridi
    Intellectual 595 points

    Thomas, 

    I have another question of chip OPA551 that I couldn't find in datasheet. According to datasheet the chip is capable of giving us up to 200mA at the output while being supplied by ±30V.

    If we supply it with ±15V, is there gonna be any problem with the output current? 

    Farzaneh

  • 0 in reply to Farzaneh Faridi
    TI__Guru* 93105 points

    Hello Farzaneh,

    I'm glad you were able to get the OPA551 Pspice simulation working. Operating the OPA551 with +/-15 V supplies is fine. Doing so will actually reduce the op amp's power dissipation and internal junction temperatures compared to when +/-30 V supplies are applied for the same 200 mA output current.

    Good luck with your application circuit!

    Regards, Thomas

    Precision Amplifiers Applications Engineering