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LM536003 PSpice Simulation Convergence

Leonard Baker
Prodigy 40 points

Hello,

I started looking into the LM536003 as an option for a 3.3V source. The Webench circuit looked pretty simple, so I download the encrypted PSpice model to start working with it for my application. I'm having convergence issues that I can't get passed.

I need an input ripple filter on the design, so I had Webench add in it's calculated version. If I run the example Startup Transient simulation included as an example in the PSpice model package, it runs as advertised. If I add in any resistance to Vin (either as an equivalent impedance using an inductor or as part of the input ripple filter) then the simulation fails to converge. At this point no combination of tricks I know for improving convergence in PSpice has worked.

If you want to try creating this, the only components added to the packaged example are for the input ripple filter: a 4.7u cap (3 mohm ESR, Cf_inpflt), a 120 nH inductor (86 mohm DCR, Lf_inpflt), a 100 mohm resistor (Rd_inpflt), and a 22u cap (80 mohm ESR, Cb_inpflt).  

This is the convergence error from the provided example when run with the input filter, all are internal to the LM536003 (U1) with the exception of the voltage source (V2). The convergence issue appears at about the time soft start would end:

ERROR(ORPSIM-15138): Convergence problem in Transient Analysis at Time = 3.604E-03.
Time step = 596.3E-21, minimum allowable step size = 1.000E-18

These voltages failed to converge:

V(X_U1.U4_N08977) = -31.25mV \ 7.813mV
V(X_U1.U4_N08957) = -17.35mV \ 303.25uV
V(X_C1._SR) = -1.986mV \ -608.51uV

These supply currents failed to converge:

I(X_U1.E_U7_ABM3) = 976.88uA \ 488.60uA
I(X_U1.E_U2_E2) = -51.81nA \ 14.47nA
I(V_V2) = 0A \ 3.906mA
I(X_U1.V_U4_V8) = 974.98pA \ -622.09pA
I(X_U1.V_U4_V7) = -964.25pA \ 623.69pA
I(X_U1.V_U1_V6) = 947.65pA \ -615.42pA
I(X_U1.X_U4_H2.VH_U4_H2) = 17.35mA \ -303.25uA
I(X_U1.X_U4_H1.VH_U4_H1) = -31.25mA \ 7.813mA
I(X_U1.X_U4_H2.H_U4_H2) = 17.35mA \ -303.25uA
I(X_U1.X_U4_H1.H_U4_H1) = 31.25mA \ -7.813mA

Thanks for any help or ideas to get past this.

Lenny

  • 0
    TI__Mastermind 39210 points

    Hi Lenny,


    Please try the following

    (1) Increase Vntol to 10u and Iabstol to 1u

    (2) If (1) does not work, in addition try increasing ITL4 to 1500

    (3) If (1) and (2) does not work, in addition try increasing Reltol to 2m (not much higher than that)

    If none of these work, please share your complete PSpice project with us so we can have a look.

  • 0 in reply to Nikhil Gupta (Product Folder Models)
    Prodigy 40 points
    Hi Nikhil,

    Thanks for getting back to me and sorry for the delay in my response.

    I've attempted your suggestions and I get the same result, a failure to converge around the time soft start would finish. There's not much special to my PSpice project. If you want to replicate it, this is all you need:

    (1) Open the example Startup Transient project included with TI's encrypted PSpice model
    (2) Add in source impedance as is shown in WeBench (500m, 1uH) in series with the supply voltage
    (3) Add in an input EMI filter with using WeBench's selected filter using a 4.7uF/3mOhm ESR (Cf_inpflt) cap on the supply side, a 120 nH /86mOhm DCR inductor (Lf_inpflt), and a series combination of a damping resistor of 100mOhm (Rd_inpflt) + a damping cap of 22uF/80mOhm ESR (Cb_inpflt) on the controller side

    Regards,
    Lenny
  • 0 in reply to Leonard Baker
    TI__Mastermind 39210 points
    Hi Lenny,

    Can you share your files with me (preferable) and/or a PDF of the schematic (second preference)? This will help me address your exact circuit.