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TPS25980: EN input operation: Pspice model

Mikhail Pavlovets
Prodigy 20 points
Part Number: TPS25980
Other Parts Discussed in Thread: TPS25982

Hello,

Dear Sirs,

A problem with the simulation model or integrated circuit? In simulation circuit I use EN input to switch ON/OFF of the TPS25980 (TPS25982) IC.

In case of EN input change to low state, the output is disable after approximately 0.7ms, and output capacitor is discharged by IC with current limited only by capacitor’s ESR. Is that kind of working of real IC or only PSpice simulation model bug?

Thanking in advance

Mikhail Pavlovets

  • 0
    TI__Guru* 79181 points

    Hi Mikhail,

    Welcome to e2e. 

    When EN go low ,what is the input voltage? Is output cap getting discharged after 0.7ms ?

    Regards

    Kunal Goel

  • 0 in reply to Kunal Goel
    Prodigy 20 points

    Input voltage is 24V (no change). Yes, output capacitance is fast discharged after 0.7ms (delay time) when EN is changed to low level.

  • 0 in reply to Mikhail Pavlovets
    TI__Guru* 79181 points

    Hi Mikhail,

    IC functionality is that when you make EN low the device will turn off within some us delay which will depend on the RC time constant at output pin. When device turns off and input voltage is 24V ,then current cannot flow back towards supply and output cap will discharge current through output resistance. Can you share model file or waveforms ?

    Regards

    Kunal Goel

  • 0 in reply to Kunal Goel
    Prodigy 20 points

    Hi Kunal Goel,

    I would like to thank you for the fast reply.

    My understanding of IC operation is the same, and I didn't find any discharge circuit inside (according to data sheet).

    Unfortunately, I can't attach files with pictures of test simulation circuit and results with comments. It is simple test circuit (input and output cap, load resistance and enable pulse). According to simulation, if ESR of output capacitor is 0.2 ohm, then discharge current peak is approximately -80A (flowing to inside IC).

    Yours, respectfully

    Mikhail Pavlovets

  • 0 in reply to Mikhail Pavlovets
    TI__Guru* 79181 points

    Hi Mikhail,

    The model may not be accurate for response time but the current should not go back into IC. Are you using Pspice? Are you facing issue in uploading files or the circuit is under NDA? 

    Regards

    Kunal Goel 

  • 0 in reply to Kunal Goel
    Prodigy 20 points

    Hi Kunal Goel,

    I use OrCAD (PSpice) release 17.4-2019. You may repeat my simulation with using simulation file of Webench Design Center (uploading files slvmd39.zip). You have only to modify EN input circuit: instead resistor divider use pulse source (Td=0.5ms, Tw=12ms, T=50ms, Tr and Tf =20us, simulation profile is no change). In this case, back current peak is >110A.  

    But, this problem is not related to simulation model, the main question is real IC operation. In TI data sheets of TPS25980x (and TPS25982) there is information (waveform) about start up with using EN input, but I didn’t find waveform in case of disable IC with using EN input.

    Can you provide information with measured waveform of output current and voltage during disable IC by EN input?  

    Best Regards

    Mikhail Pavlovets

  • 0 in reply to Mikhail Pavlovets
    TI__Guru* 79181 points

    Hi Mikhail,

    I can provide waveform. Do you have EVM for your evaluation? Evaluating device with EVM will give you a better picture 

    Regards

    Kunal Goel

  • 0 in reply to Kunal Goel
    Prodigy 20 points

    Hi Kunal Goel,

    If I had the EVM, then I would have no questions for you!

    Thank you

    Best Regards

    Mikhail Pavlovets

  • 0 in reply to Mikhail Pavlovets
    TI__Guru* 79181 points

    Hi Mikhail,

    I can share waveforms by mid next week.

    Regards

    Kunal Goel

  • +1 in reply to Kunal Goel
    TI__Guru* 79181 points

    Hi Mikhail,

    Please have a look at waveforms. They clearly show that no reverse current flow is there.

    1. 3A load 

    2. Only capacitive load 

    Regards

    Kunal Goel