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Some questions for voltage controlled current source chip, like OPA860.

Luxing Wang
Prodigy 160 points
Other Parts Discussed in Thread: OPA860, TINA-TI, OPA615, LMV7219

I just searched for a voltage controlled current source IC, with wide bandwidth above 50MHz, high adjustable trans-conductance and wide linear range. By comparison, I think OPA860 maybe work. (Actually, I am worried of my searching method, and maybe there are other better VCCS chips.) However, the datasheet is not clear enough.

(1) For the typical connection, the load is resistance. In my application, the load will be the capacitance.Therefore, I am worried whether or not it can still work linearly. 

(2) The graph of the relationship between input voltage and output current is only within the range of from -70mV to 70mV, and has no idea of the relationship above this range. Therefore, will it be still linearly beyond this input voltage range? Actually, maybe I hope it can be linear from -200mV to 200mV.

(3) In my application, I may need use this chip in parallel. Will it have some imbalance problems during this application? And what kind of problems? Generally, how to avoid it?

I am looking forward to some reply and answers. Thanks a lot.

Lucy

  • 0
    TI__Genius 12631 points

    Hello,

     You can use TINA-TI a SPICE simulator to check the performance from -0.2 to 0.2V. I have attached a test circuit. You can modify it to the circuit in Figure 48 which is how the +/-70mV circuit was configured.

    For paralleling multiple chips I would use an isolation resistor of 10-20 ohms on each C-output before I connect multiple channels together. This series resistor will also help in isolating the OTA from the capacitor load. You could try this isolation resistance in simulation as well. Since this is an open-loop, current output device I am not sure if it is really needed but would advise to add it on your PCB and then install a 0 ohm resistor if it turns out that the isolation is not needed.

    Another option is the OPA615 which does show a +/-200mV input range (Figure 4) so maybe this is the best choice.

    A test PCB (unpopulated) for the OPA615 and OPA860 is available on www.estore.ti.com. The price varies from free to $5. You can also get some free IC samples there to check your design.

    -Samir

    6366.OPA860 IQ.TSC

  • 0 in reply to Samir Cherian
    Prodigy 160 points
    Hi, Samir:
    Thanks for your reply. I have tried the OPA860 you offered to me in TINA. One question: there is a offset voltage( when input voltage is zero, there is a negative current flowing into the pin and create negative voltage. ). Is it a feature for this chip, which means in the real case, it will have this problem? How to eliminate this impact? Because it may have bad influence on my application.
    I also found PSIPCE mode for OPA615 in our website, but it cannot insert into TINA. Therefore, I had to insert it into SIMEtrix and simulate it. I found it also had the offset voltage problem, which is positive.
    In addition, because I want to compare OPA860 and OPA615 clearly, therefore I want a TINA Model for OPA615. I also want the PSPICE model for TL714C and LMV7219 which I also need to use. Note: It seems like the model has to be .sub or .txt or something like this.
    I am looking forward to your reply.
    Best wishes,
    Lucy
  • 0 in reply to Luxing Wang
    TI__Mastermind 22825 points

    Hi Lucy,

    Have you looked here (I can see the LMV7219, and OPA615 here):

    Also, the LMV7219 can be found in TINA-TI directly by clicking "Find Component" finger icon in the upper RHS.

    Regards,

    Hooman

  • 0 in reply to Hooman Hashemi
    Prodigy 160 points

    OPA615 has a PSPICE model but not a TINA one. Actually, I have no idea of how to insert a .txt format to TINA, so that I cannot use LMV7219 in SIMetrix. Even this guy has a PSPICE model, it is different from others, which is not a .txt format but a .mod, so that I cannot insert it directly in SIMetrix.

    In addition, I also have no idea of inserting a TINA model to PSPICE.

  • 0 in reply to Luxing Wang
    TI__Mastermind 22825 points
    Hi Lucy,
    I've moved your question to the Simulation Models Forum for better support.

    Regards,
    Hooman
  • 0 in reply to Luxing Wang
    TI__Mastermind 41310 points

    Luxing,

    I understand your confusion. Lets start with some basics:

    1.) A PSpice model can be imported into any simulator that supports PSpice model import. SIMetrix and TINA-TI both support PSpice model import.

    2.) All simulators seem to have a different way to import models. You will have to know how your simulator works in order to import the PSpice model into your simulator.

    3.) There are many extensions on model files (.txt, .mod, .lib, .cir, etc.). All of these files are text files and you can view them in any text editor. You can easily rename the model file to the proper .lib extension and it should import correctly into your chosen simulator. For the LMV7219, simply rename the file to LMV7219.lib and follow the procedure for importing the file into your simulator. For the OPA615_Model.sub file, simply rename it to OPA615.lib and import it in normally.

    4.) If a PSpice model file is encrypted (you can tell because the model file lines that are not comments are unreadable with a normal text editor and appear to be gibberish), you must obtain the unencrypted PSpice model to import it into any other simulator. PSpice models that are encrypted can only be used with PSpice version 15.7 or higher.

    5.) TINA-TI has a very good set of videos detailing how to use the tool. The video training series can be seen here:

    I am sure that there are some videos that can be found that can help with importing PSpice models into SIMetrix as well.

    Please note that you cannot simply insert a PSpice model into any simulator other than PSpice. The model will have to be imported which creates a symbol and the proper connectivity for the model so that the simulator may use the model. Additional changes to the model may be required as the level of PSpice compatibility for simulators varies. Most of the time, no changes are necessary.

    Finally, if the model is imported properly and the circuit is created, there is still no guarantee that the circuit simulation will run. You may still have to tune the simulation parameters to get the proper performance from the circuit. This also requires that you know a little bit about how your simulator works and what changes are required to make the circuit simulate properly.

    I hope this information helps.

  • 0 in reply to Britt Brooks - Online Design Tools
    Prodigy 160 points

     Thanks so much. I will watch that training in order to have a better understanding of it. 

          Best wishes,

           Lucy