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Original question:

TINA/Spice/LM5176: LM5176 Spice Model

LM5176: LM5176 TINA Model, Soft Start does nothing?

j0ule
Prodigy 30 points
Part Number: LM5176


Tool/software:

Hello there,

I have been simulating using the model provided here 

https://e2e.ti.com/support/tools/simulation-hardware-system-design-tools-group/sim-hw-system-design/f/simulation-hardware-system-design-tools-forum/759691/tina-spice-lm5176-lm5176-spice-model

However, the SS pin doesn't appear functional?

When Vss drops to 0, due to hitting I limit, the switches keep switching unabated as if nothing happened.

 

LM5176.TSC

Is the model incomplete?

There is an undocumented subckt parameter, SS, which shows the same behavior when set to 0, or 1

I also tested the model that was exported from WeBench, with the same result: SS doesn't influence the switches.

  • 0
    TI__Guru 60821 points

    Hi,

    thank your for using the E2E forum.

    We will have a look into that and come back later this week.

    Best regards,

     Stefan

  • 0
    TI__Mastermind 31840 points

    Hi J0ule,

    Thanks for using the e2e forum.

    I double checked this TINA testbench and saw the same error. The softstart is not functioning as it should be.
    The thread mentioning this model is over 6 years old and we do not promote a TINA model on the product page, so it might be outdated.

    The most updated model for LM5176 is available in PSpice and can be downloaded from the product page:
    https://www.ti.com/lit/zip/snvmba4

    I verified the functioning of the softstart in this model and can confirm it operates properly.
    If possible, please use this PSpice model for your design simulations.

    Best regards,
    Niklas

  • 0 in reply to Niklas Schwarz
    Prodigy 30 points

    Niklas,

    Thank you for verifying, I thought I may have been doing something wrong. 

    May I have a copy of the unencrypted pspice model to import into TINA?

    The pspice interface is very difficult and unintuitive, we have a lot of schematics in TINA due to this. 

    -j0ule

    Edit:

    Oops, I am sorry, I see the model was released as unencrypted already, in 1.30.

    I will try it now!

  • 0 in reply to Niklas Schwarz
    Prodigy 30 points

    Niklas, 

    I tried the PSPICE model, and found the same issue. SS does not have any effect. 

    But now that the model is unencrypted, we can have a closer look as to maybe why?

    There is a subcircuit parameter in the first few lines:

    PARAMS: SS=0

    Near the end of the LM5176 model, we find:

    + OR3_BASIC_GEN PARAMS: VDD=1 VSS=0 VTHRESH=500E-3
    .IC V(VCC )={{SS}*7.5}
    .IC V(CLK_RESET )=0
    .IC V(OSC_N16673143 )=0
    .IC V(OSC_N16673175 )=1
    .IC V(SS )={{SS}*1.22}
    .ENDS LM5176_TRANS

    This SS parameter is seemingly used to calculate V(SS)

    It seems SS is not defined by a pin, but is defined explicitly as 0?

    This would mean V(SS) is always 0, which seems improper.

    So, I set the subcircuit parameter to = 1, which would mean V(SS ) = 1.22, in agreement with the datasheet.

    But we still see the same behavior, the switching is not reduced as the soft-start pin voltage decreases.

    Even as the voltage across the ISNS pins approaches 200mV, no current is reduced.

    Edit: Attach TINA file

    1258.LM5176.TSC

  • 0 in reply to j0ule
    TI__Mastermind 31840 points

    Hi J0ule,

    Thanks for the update and all the investigation you did already.

    The SS value should be just a flag that can be set to skip softstart and reach steady state operation faster to reduce simulation time.
    SS = 0: Device starts up normally with softstart
    SS = 1: SS voltage is pulled high right from the start, Sofstart is skipped

    You mentioned you tried the PSpice model as well. Are you sure softstart is not working in PSpice either, or did you see this behavior just in TINA?
    When I simulated in PSpice, the softstart was operating fine.
    To run the simulation in TINA, I assume you transferred the unencrypted netlist to the other simulator. Could it be that an error occurred during the transfer between TINA and PSpice?

    Best regards,
    Niklas