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INA381: INA381 Alert is not locked for the first time

Katherine Wang
Intellectual 2210 points
Part Number: INA381
Other Parts Discussed in Thread: TINA-TI

Hi Team,

The figure below is the simulated waveform

When INA381 reset is connected to high level electricity, the Alert is not locked for the first time. It's only locked for the second time. Could you please tell me why?

Kind regards,

Katherine

  • 0
    TI__Expert 4720 points

    Hello,

    Is this a simulated waveform on Pspice? If so the INA381 model has a limitation this should not be the case. In real operation if the reset is high the INA will latch.

    Thank you for finding this. I will speak to the team to fix this.

    Regards,

    Cas

  • 0 in reply to Castrense Nigrelli
    TI__Intellectual 2210 points

    Hi Castrense,

    The customer replied that it was simulated on PSPICE, and the model was downloaded from the official website. He requested that someone check whether this issue did exist on the model. 

    Regards,

    Katherine

  • 0 in reply to Katherine Wang
    TI__Expert 4720 points

    Hello,

    I also simulated this in TINA-TI with the official model and got similar results that is why I believe the models are incorrect I will check with the model expert on our team to better understand this.

    Regards,

    Cas

  • 0
    TI__Mastermind 30035 points

    Hey Mason,

    There does seem to be a bug with the simulation model when operating in LATCH mode. I can see that this bug is fixed when you select the "SKIPBP" option in the Edit Simulation Profile settings.

    For TINA, to fix this you need to select either "Use initial conditions" or "Zero initial values" in the Transient Analysis options.

    Sincerely,

    Peter

  • 0
    TI__Intellectual 2210 points

    Hi Team,

    1. "SKIPBP" has been selected in the settings, but it still cannot be locked for the first time; we found that if the Rate of Change of Current decreases, it can be locked for the first time. I wonder if the input of the latch needs a settling time and maintenance time?

    2. Could you please tell me why it can't be locked only for the first time?

    3. We also tried, if we do not select "SKIPBP", it will not be locked.

    Regards,

    Katherine

  • 0 in reply to Katherine Wang
    TI__Mastermind 30035 points

    Hey Katherine,

    If reducing the Rate of Change of Current fixes the issue, then reducing the "Maximum Step Size" time should also help.

    Either way this is just a simulation model issue, not a real-world device issue.

    The root cause has to do with how sim model internally sets the digital level of RESET pin at the very beginning of the sim. If SKIPBP is not selected, then software will try to establish a stable DC bias operating point before beginning the transient sim. The ALERT pin is controlled by some non-ideal switches (voltage-controlled resistors), which can sometimes have trouble converging if using a high simulation conductance parameter and/or if the range between Roff and Ron is very large. There is also a capacitor at the input to these switches, perhaps there must be  some transient time to pass before a deterministic solution for the switches can be achieved and thus it is not a good idea to try and determine this before beginning the transient sim (SKIPBP not selected).

    Best,

    Peter