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TL331 pspice model

Nebiate setegne
Prodigy 10 points
Other Parts Discussed in Thread: TL331, LM7171

I am using TL331 comparator on my project5383.help for TI_TL33.docx. I am using it on simulation on pspice model that I obtain from TI website. I am using it to create pwm signal out put using TL331 components. I am trying to use TL331 components to create PWM. on the negative input side has pwm signal source and the positive side of the input 2.5 v dc. the goal is when negative input is smaller than the positive input then out put rises and stays at 15 v. until the negative input signal is smaller than the positive input signal. if the positive input is smaller than negative input, the output would be goes to zero. the problem I am having is when the negative input is smaller than the positive input, the output won't rise to 15 v right at the point. it takes about 2 micro second then it goes to 15V. I am trying to figure out why is doing that on TL331 pspice model. I used different model of comparator to see if the problem was the circuit. I used LM7171AIN and it works right. I was wondering if you would have any idea why is doing that. I would appreciate your help. thanks!]

  • 0
    TI__Guru 60016 points

    Hello Nebiate,

    You are seeing prop delay. This is the major spec of a comparator. The TL331 has a typical of 0.3 to 1.3us, depending on input level. Your input step is large, so you should be seeing about 300ns.

    Where did you get the model? Was it the one that came with Orcad? Or did you get it from TI?

     http://www.ti.com/lit/zip/slvm937

    The official TI model above has a fixed 700ns prop delay at 5V. Some models are not "smart" enough to vary the prop delay with the input amplitude, so they use a fixed delay time. 700ns in this case.

    * Notes:
    * 1. The following parameters are being modeled at +5V operation:
    *    IIB, IOS, VIO, AVD, VICR, VOL, IOL, ICC
    * 2. Response Time does not vary with input level, and is equal to
    *    approximately 700ns at +5V operation.
    * 3. This model is intended to work with single supplies, e.g. {+VCC,GND}
    * 4. This model is based on data sheet parameters for +5V operation.
    *    It is unknown if this model will match device behavior at
    *    other power supplies.

    You may be able to tinker with the value of CG1 in the model to change the speed.

    And, by the way, the LM7171 should NEVER be used as a comparator. It will damage the inputs and will draw excessive supply current when the output is slammed against the rail. The 7171 will work in the SPICE world, but will have problems in the real world.

    Regards,