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Original question:

ATL431 SPICE model problem

ATL431: ATL431 SPICE model startup problem

Sebastian Reinig
Prodigy 10 points
Part Number: ATL431
Other Parts Discussed in Thread: TL431

Hello,

there seems still to be the issue with start-up response of the ATL431B model which is different to the start-up response shown in the datasheet. The issue was also part of a discussion about the ATL431A model: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/516726/atl431-spice-model-problem?tisearch=e2e-sitesearch&keymatch=ATL431%25252520Model# 

For my simulation I used the "ATL431B Unencrypted PSpice Transient Model" from the download page and imported it to LT-Spice: https://www.ti.com/product/ATL431#design-development

The following picture shows the simulation result from LT-Spice with the test circuit of the datasheet. I also attached the LT-Spice simulation file.

Test ATL431_test_circuit.zip

Is there a way to fix this problem?

  • 0
    TI__Mastermind 47445 points

    Hi,

    Unfortunately, we do not support LT Spice so I am unsure how to address your concerns.

    Ben 

  • 0 in reply to Ben C
    TI__Mastermind 47445 points

    Hi,

    If there are no further questions, please close the thread by clicking on "resolved".  Thanks!

    Ben

  • 0 in reply to Ben C
    Prodigy 10 points

    Hi Ben,

    I imported the same model library to the "PSpice for TI" simulator and rebuilt the test circuit of the datasheet as the attached schematic shows. The described problem at the start-up sequence still exists. 

    Sebastian

  • 0 in reply to Ben C
    Prodigy 10 points

    Hi Ben,

    I imported the same model library to the "PSpice for TI" simulator and rebuilt the test circuit of the datasheet as the attached schematic shows. The described problem at the start-up sequence still exists. 

    Sebastian

  • 0 in reply to Sebastian Reinig
    TI__Mastermind 47445 points

    Hi Sebastian,

    Try adding some capacitance on the cathode and reducing the VIN slew rate of the power supply.  It is unlikely that the VIN slew rate can slew up to its intended voltage in 10ns.  Also, I believe the model has limited bandwidth and hence the "response delay".

    Ben  

  • 0 in reply to Ben C
    TI__Mastermind 47445 points

    Hi,

    Are there any updates?

    Ben

  • 0 in reply to Ben C
    Prodigy 10 points

    Hi Ben,

    when reducing the ramp time of the voltage source to 1µs and adding a capacitance at the cathode I get the following results: 

    a) simulation with a 10nF capacitor.

    b) simulation with a 100nF capacitor

    When I use a larger capacitance I get a reduction of the overshoot but a very slow startup compared to the datasheet. Also an oscillation is added to the ramp when using the capacitor at the cathode.

    Sebastian

  • +1 in reply to Sebastian Reinig
    TI__Mastermind 47445 points

    Hi Sebastian,

    See figure 14 below.  Try adding a larger capacitor on the output.  I believe you are operating in the unstable region.  Also, have you tried slowing down the slew rate of VIN?  The model may not be a perfect representation of the actual device but it does yield a similar performance behavior. 

    Reading other e2e threads, this issue that you have brought up has been mentioned before.  Have you tried TL431's spice model? 

    Ben