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TPS3808: Simulation in TINA-Ti with hysteresis

Martin Sauer
Prodigy 70 points
Part Number: TPS3808
Other Parts Discussed in Thread: TINA-TI

Tool/software:

Hi,

I want to simulate a design according to https://www.ti.com/lit/an/slva360/slva360.pdf in TINA-TI. I calculated the needed resistor values for a hysteresis between 9.3V and 17.1V.

But the simulation didn't work.

I would have expected the signal RESET_BAR_ctopen to go up at 9.3V and down at 17.1V.

Do you know where my problem is?

Thank you for your help.

BR

martin

  • 0
    TI__Expert 6660 points

    Hi Martin, 

    Thanks for your question!

    I don't think the model is fully capable to show the expected behavior when there is a hysteresis resistor in the feedback loop as indicated in the app note. I quickly tried to simulate your circuit and I wasn't even able to get the expected hysteresis behavior.

    But the concept should be correct as long as you have correct R1 and R2( the RESET will be low, when the monitored voltage is go below 9.3V and the RESET will be high again once monitored voltage go above 17.1V. Could you please first clarify if this is your intended the way of application?  

    Martin Sauer said:
    I would have expected the signal RESET_BAR_ctopen to go up at 9.3V and down at 17.1V.

    Thanks,

    Sila 

  • 0 in reply to Sila Atalar
    Prodigy 70 points

    Hi Sila,

    yes. 9.3V is switch off and 17.1V is switch on.
    I can do the simulation if I set Ct to 100pF, but the switch on voltage is about 17.1V and depends on the voltage ramp of VSENSE.

    BR

    martin

  • 0 in reply to Martin Sauer
    TI__Expert 6660 points

    Hi Martin,

    Yes, the slew rate can be important. Do you know what will be your slew rate for VDD and Vsense in your application?

    And can you please let me know when you increase the rate of change of your input voltage, were you able to get the expected hysteresis result on simulation work?

    Best,

    Sila

  • 0 in reply to Sila Atalar
    Prodigy 70 points

    Hi Sila,

    sorry, I don't know the slew rate.

    The switch on voltage is about 22.32V and the switch off is at 9.3V.

    Is this a simulation error?

    BR

    martin

  • 0 in reply to Martin Sauer
    TI__Expert 6660 points

    Hi Martin,

    I think the simulation seems like it's working. The resistor divider values are very important in this design. 

    To answer your question, I would change the resistor values and see what is happening to the Reset signal. When reset de-assertion occurs (reset become high) for different resistor divider values. This way we can understand if the simulation works or not. 

    Hope this helps!

    Best,

    Sila Atalar