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LM5021: LM5021 Max value of Vin in normal operation

Part Number: LM5021
Other Parts Discussed in Thread: PMP7188, , TINA-TI

I simulated PMP7188 in LTspice.

Basically,it can work.

But I discover that the value of  Vin is greater than 36(typ Vin ESD) in the beginning.

fig1.voltage and current waveform of  VIN

Theoretically, Vin should be clamped between 30~40.
Is it possible that Vin>40?

or it is a error of LTspice?

fig2.datasheet of LM5021

plz help me with this problem.m(_ _)m

fig3.Schematic

PMP7188.rar

  • Hi,
    Thank you for your interest in TI here. I've contacted the appropriate engineer that supports this device. You should hear from him tomorrow morning US Eastern Standard Time.
    Regards,
    John
  • Thank fot your help
  • Hello user4843850,

    This issue is undoubtedly a result of some problem with the simulation model, not of the real part.
    Based on the schematic diagram, 2Mohm on a 375-Vdc bulk rail will provide at most only 188uA of charge current to C7. This current should take ~1.1 seconds to charge C7 to 20V, and longer start time at lower input voltages. Your simulation shows an almost instantaneous jump to 58V, followed by what appears to be some start-up activity about 10ms later. Since this is not the expected behavior based on consistent real-world experience, and simply doesn't make sense based on calculations, we can conclude there is something wrong with the model at start-up. I am assuming that C7 does not have an initial condition = 58V. Please check this.

    We cannot make any conclusions beyond this, such as whether or not the model works okay in long-term steady-state conditions or during transient disturbances, based only on the 260ms simulation segment that you presented. However the failure of the simulation to accurately reflect the start-up does call into question the overall accuracy of that IC model for follow-on simulations of complex system interaction. It is difficult for me to have faith in a model that cannot recreate one of the basic functions of the IC, including clamping the Vin node to 36V. TI cannot vouch for the veracity of a competitor's model of a TI device or their simulation program.

    TI provides a PSpice model and a TINA-TI model for this part. I suggest that you try using the TINA-TI modeling program with the same circuit.

    Regards,
    Ulrich
  • I will try it again by using TINA-TI
    Thanks for your explanation !

    Can you run a simulation and post the voltage and current waveform at a point( Vin)of LM5021, if it is possible that you have the simulation file of PMP7188.
    I would be most appreciative!!m(_ _)m
  • Hello,

    I am sorry to disappoint you in that I am not able to answer your request to set up and run a simulation for the LM5021. I simply do not have the time for this, since in general the TI support for the E2E forum comes from engineers who have other jobs with tight schedules, and are not dedicated to solely support the forums. But E2E is not limited to TI responses, so if other interested viewers have time available and are willing, I invite them to try this simulation and post the results.

    Regards,
    Ulrich