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Original question:

LM5176: LM5176

LM5176: Simulation results

Dimitris Rodas
Prodigy 10 points
Part Number: LM5176


Hello,

I am currently designing a buck converter that is going to be used in our Formula Student vehicle. I think that the LM5176 is a giid choise as it includes features such as high Vin range and Iout. To ensure that the design will run as expected i have run the simulation that you provide in pspice with gust changing Vin and the feedback voltage divider (I want Vout = 24V and i have used R1 = 280k, R2 = 10k ). The problem is that is the simulation Vout reaches max 21.5V, is this a simulation problem or am i doing something wrong.

Thanks for your time.  

  • 0
    TI__Guru 60671 points

    Hi Dimitris,

    please note that the LM5176 is Buck Boost. So if you only need a Buck another device might be a better fit.

    Can you share your simulation file to review and check.

    Best regards,

     Stefan

  • 0 in reply to Stefan Schauer
    Prodigy 10 points

    I like the buck boost function because the input might got a bit lower that 24V so its ok. Here are the files that i am simulating3157.LM5176.zip

  • 0 in reply to Dimitris Rodas
    TI__Guru 60671 points

    Hi Dimitris,

    please allow us a few days to look into that - PSpice simulation take some time.

    Will come back beginning of next week.

    Best regards,

     Stefan

  • 0 in reply to Stefan Schauer
    TI__Mastermind 31770 points

    Hi Dimitris,

    I had a look at your simulation model and as you already stated, the schematic is still the default testbench with only minimal changes on VIN and VOUT.

    The default setup should run just fine for the default parameters.
    As soon as you make modification on parameters like VIN and VOUT, without adjusting load, inductance, switching frequency or compensation, it is possible that the design becomes unstable, as it is not optimized for the given parameters.

    The first thing I would recommend is to double check the schematic with the help of our quickstart calculator.
    https://www.ti.com/tool/download/SNVC208
    Please select inductance, switching frequency, current sense resistors and compensation values to match your design goals and then adjust the simulation model accordingly.
    Also please make sure the resistive load is not too high in the simulation, so you do not trigger overcurrent protection unintentionally.
    If you then still have problems with the simulation results, we can go through the design together and look for possible root causes.

    Best regards,
    Niklas