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TINA/Spice/THS4221: Simulating THS4221 in Tina-TI

Hong Pan
Prodigy 245 points
Part Number: THS4221
Other Parts Discussed in Thread: TINA-TI,

Tool/software: TINA-TI or Spice Models

Hi,

I am doing a simple simulation using THS4221 as a comparator. Please see the schematic below:

Battery = 10V

VG1=Square wave at 1kHz switch between 0 to 5V

Voltage at V+ terminal of THS4221 stays in between 2.3V and 2.7V because resistors are set up for having a few millivolt of hysteresis for this comparator configuration.

The result says THS4221 is drawing 23A of current. What did I do wrong? 

Thanks

  • 0
    TI__Genius 15565 points

    Hello Hong,

    For your comparator design, I believe you want to use R1 and R2 as a voltage divider and connect that to the non-inverting node as shown below:

    That being said, the THS4221 model was not meant to be used in this fashion where it is driven outside its input common-mode range and has a large input differential voltage. Please take a look at our comparator portfolio that would be much better suited to your design:

    Best,

    Hasan Babiker

  • 0 in reply to Hasan Babiker31
    Prodigy 245 points

    Hi Hasan,

    You were right about that my connection to the V+ terminal was incorrect. I fixed it and did another simulation, it still draws 4.4A of current from the power supply. Please see the new screen shot below.

    My common mode input range is +1.35V<Vcm<+3.65V. It's within the recommended range according to the spec on the second page of the datasheet. Differential input range is less than +4V which is also within the spec called out in the datasheet. Do you have any idea where the large current draw is coming from? 

    I am using THS4221 to drive a capacitive load (about 3.5nF). I would like to have both the rise and fall time to be less than 100ns. In my case, slew rate and current capacity of the amp are important, and I care less about the propagation delay. I have not found a comparator that comes close to what THS4221 can do. Comparators do not have enough current source or sink capability to get it done. Other amps with large current capacity have slow slew rate. I did another simulation with THS4221 where I increased common mode input range on the low end (1.64V<Vcm<3.94V), the current is still very large (about 4A).

    If you can, please recommend an op amp that will do what I want to have. I would love to understand why THS4221 is drawing 4A of current in my simulation.

    Thanks

  • 0 in reply to Hong Pan
    Guru 140200 points
    Hi Hong,

    I don't think that the model of THS4221 will correctly model the supply current of THS4221, if at all.

    Kai
  • 0 in reply to kai klaas69
    Prodigy 245 points

    Hi Kai,

    I do not understand why a model cannnot predict the overall current going into one node if every element inside a model is correct. That's what node method is all about. 

    Do you think it will model it's current output capability and slew rate correctly in the simulation?

    Thanks.

  • 0 in reply to Hong Pan
    Guru 140200 points

    Hi Hong,

    yes, everything which has to do with the signalling should be modelled correctly, usually.

    But exotic issues are not modelled properly, if the input voltage exceeds the supply voltage, for instance, or the supply current, etc. This heavily depends on the date of manufacture of model: The older the model the less is modelled, the newer the model the more is modelled. And as the Spice model of THS4221 is from 2003, I think that the supply current is not modelled.

    Kai