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LM7481-Q1: How to connect RTN in encrypted SPICE model

Oscar Hernandez
Prodigy 10 points
Part Number: LM7481-Q1
Other Parts Discussed in Thread: LM7481

Hello TI support.

I'm trying to simulate the LM7481-Q1 with the PSPICE for TI software. I made the following circuit as an initial test.

I imported the NMOS and controller models using the "Generate Part" option. The library models are also referenced in the settings.

When I try to run a simple transient simulation, the tool tells me that there a node has less than 2 connections.

ERROR(ORPSIM-15141): Less than 2 connections at node N22830.

This node is tied to the RTN pin:

X_U4         N15692 N15887 N16831 N16520 N19120 0 N16179 N16527 N16021 N22830

I understand that the pin 13 is NC from the datasheet, so in the simulation I connected a 1Mohm resistor. Yet still the tool shows me an error. 

How can I solve this? Is there an special connection needed here?

  • 0
    TI__Guru 57737 points

    Hi Oscar,

    PSPICE for TI software has a limitation on the number of voltage/current signals you can monitor at a time. Can you reduce the no. of probes connected to monitor the voltage/current waveforms to 2 or 3.

  • 0 in reply to Praveen GD
    Prodigy 10 points

    Hi Praveen, thanks for the reply. I have not connected any probe yet. My first step was to just simulate the circuit without any errors, unfortunately I get this error.

    I have additional information: I removed the 1 Mohm resistor to the RTN pin and connected RTN directly to GND. With this action, the node with less than 2 connections error disappeared but obtained another error:

    ERROR(ORPSIM-16583): Detected an imported model containing transistors or diodes. For such models, PSpice for TI supports a minimum of one and maximum of three traces. Reduce the number of traces and simulate again.

    At first I thought this was related to the imported NMOS BUK7J1R0 I used so I removed it from the schematic and used a MOSFET that is preloaded in the PSPICE Library.

    However, the same error appeared, I checked the report and found that there are 4 MOSFETs in the design. My guess is that they are the 2 I used and 2 inside the LM7481 model, there are also 8 diodes reported and I am not using any diode.

    Total device count (NUMEL) = 89
    Capacitors (C) = 23
    Diodes (D) = 8
    VCVS (E) = 0
    VCCS (G) = 0
    Inductors (L) = 8
    MosFETs (M) = 4
    Resistors (R) = 36
    VSwitches (S) = 0
    Voltage Sources (V) = 2

    I think then that I won't be able to simulate this model with PSPICE for TI due to the limitation of maximum 3 traces, this model is not in the official PSPICE library.

    Is there a way to tell the tool to not consider this as an imported mode? or Can I get the unencrypted SPICE model file? My company has a NDA signed with TI.

  • 0 in reply to Oscar Hernandez
    TI__Guru 57737 points

    Hi Oscar,

    If you have an NDA with TI, we can share the unencrypted PSpice model with you. Please reach out to the FAE supporting you.

  • 0 in reply to Praveen GD
    TI__Guru 57737 points

    Hi Oscar,

    I am closing this thread here as I have shared the Unencrypted Model with our FAE on email. You should receive it soon.

    In case you have any other questions, you can post it in a new thread.