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LM70880-Q1: Webench Design Issue - LM70880-Q1 (Insufficient Phase Margin) - 60V to 28V@6A

Lasse Jarvela
Prodigy 20 points
Part Number: LM70880-Q1
Other Parts Discussed in Thread: LM70880

Tool/software:

Hello,

I'm encountering issues generating a stable design with Webench for the LM70880-Q1. My specifications are:

  • Input Voltage: 48V - 60V
  • Output Voltage: 28V
  • Output Current: 6A

Webench consistently fails to produce a design with adequate phase margin. I suspect a potential problem with the tool or the device model. Could a TI applications engineer please review this?

Thank you.

  • 0
    TI__Mastermind 47945 points

    Hi Lasse,

    The output power (voltage and current) is too high for the LM70880-Q1. This application may need 2 X LM70880-Q1 (dual phase operation) to split the power so the IC can deliver the power without triggering thermal shutdown. Please use the quickstart calculator as an alternative to WEBENCH.

    LM70XX0_quickstart_calculator_A1.xlsm

    Ben

  • 0 in reply to Ben C
    Prodigy 20 points

    Hi Ben,

    the Excel-based quickstart calculator provides a seemingly valid design, and thermal analysis suggests it's within acceptable limits. I plan to verify this design further using TI PSpice, but I'm currently encountering license download issues, which appear to be affecting other users as well.

    My high-current load is periodic with a relatively low duty cycle, which should significantly reduce the actual heat generated by the IC compared to a continuous load scenario.

    I have attached my design for your review and would appreciate any comments or feedback you might have.

    LM70880-Q1-VIN_58V-VOUT_28V_IOUT_6A.xlsm

    Thank you,

    Lasse

  • 0 in reply to Lasse Jarvela
    TI__Mastermind 47945 points

    Hi Lasse,

    I would suggest getting our EVM and take bench data to verify the thermals of your application. In my opinion, there is no need to run a simulation on Pspice as the quickstart calculator is pretty accurate on the loop analysis.

    Attached is the quickstart calculator. I have made some changes to. The changes are to the inductor value and to the external compensation values.

    LM70880-Q1-VIN_58V-VOUT_28V_IOUT_6A_updated.xlsm  

    Ben

  • 0 in reply to Ben C
    Prodigy 20 points

    Hi Ben,

    I got the TI PSpice installed and now when I try to run a testbench example, I get weird errors (see the end of the snippet) and it aborts. Could you guys please help me? 

     3107.LM70880_V2.0.zip

    LM70880_SCH.pdf

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    ** Creating circuit file "test.cir"
    ** WARNING: THIS AUTOMATICALLY GENERATED FILE MAY BE OVERWRITTEN BY SUBSEQUENT SIMULATIONS
    *Libraries:
    * Profile Libraries :
    * Local Libraries :
    .LIB "../../../lm70880.lib"
    * From [PSPICE NETLIST] section of C:\cds_spb_home\cdssetup\OrCAD_PSpiceTIPSpice_Install\23.1.0\PSpice.ini file:
    .lib "nom_pspti.lib"
    .lib "nom.lib"
    *Analysis directives:
    .TRAN 0 3.5m 0
    .OPTIONS ADVCONV
    .OPTIONS FILEMODELSEARCH
    .OPTIONS SPEED_LEVEL= 5
    .PROBE64 V(alias(*)) I(alias(*)) W(alias(*)) D(alias(*)) NOISE(alias(*))
    .INC "..\LM70880 Test Bench.net"
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

    -Lasse

  • 0 in reply to Lasse Jarvela
    TI__Mastermind 47945 points

    Hi Lasse,

    Are you running PSpice for thermal simulations? I do not see the errors that you are describing. Did you update the PSpice program to the latest version?

    Ben

  • 0 in reply to Ben C
    TI__Mastermind 47945 points

    Hi Lasse,

    I think the PSpice model for LM70XX0/-Q1 is the older version which has since been updated.

    Please download the latest LM70XX0/-Q1 PSpice model.

    Ben 

  • 0 in reply to Ben C
    Prodigy 20 points

    Hi Ben

    Earlier today I did the exact same thing and downloaded the latest model. This time I was able to start the simulation, but weirdly enough, I get convergence issues even with the example testbench - and the same happens with my own circuitry as well... 

    I wonder if the problem is in the testbench, in LM70880 model or in my PSpice settings. Could you try to rerun the testbench on your end?

    -Lasse

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    **** 03/28/25 19:04:33 **** PSpice 23.1.0 (30 January 2024) *** ID# 0 ********
    ** Profile: "LM70XX0-Q1 Test Bench-transient" [ C:\Users\ljarvela\Downloads\snvmcd7a\LM70XX0-Q1_PSpice_TRANS\lm70xx0-q1_trans-PSpic
    **** CIRCUIT DESCRIPTION
    ******************************************************************************
    ** Creating circuit file "transient.cir"
    ** WARNING: THIS AUTOMATICALLY GENERATED FILE MAY BE OVERWRITTEN BY SUBSEQUENT SIMULATIONS
    *Libraries:
    * Profile Libraries :
    * Local Libraries :
    .LIB "../../../lm70xx0-q1.lib"
    * From [PSPICE NETLIST] section of C:\cds_spb_home\cdssetup\OrCAD_PSpiceTIPSpice_Install\23.1.0\PSpice.ini file:
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

  • 0 in reply to Lasse Jarvela
    TI__Mastermind 47945 points

    Hi Lasse,

    I do not see any issues from my end. See below:

    Ben