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LM51231-Q1: LM51231-Q1 simulation - Output voltage issue

Emmanuel Olvera
Prodigy 10 points
Part Number: LM51231-Q1

I downloaded the Pspice transient model and I configurated as the circuit that we are using. The circuit is configurated to the voltage output range of 15V-57V but when I set 0.98V to the TRK input I do not get more than 30V as output voltage.

I don’t know if there is a current limitation in the Pspice mode of the LM51231 or in the voltage source. I tried to edit them properties but I did not see any property related with the current.

  • 0
    TI__Mastermind 46251 points

    Hi Emmanuel,

    thank you using the E2E forum.

    I will double check with our PSpice expert and came back in 2-3 days.

    Best regards,

     Stefan

  • 0 in reply to Stefan Schauer
    TI__Mastermind 20510 points

    Hi Emmanuel,

    There was indeed an issue with the initial LM5123 PSpice model, which only allowed an output regulation target in the lower voltage range.
    We have uploaded a fixed version, which now works for the upper Vout range (20V-57V) as well. (This is Revision B)

    The model for LM51231 should not have this issue.

    Can you please check if you are using the correct model and the newest version?
    Please also check if the upper and lower resistors are in the correct range:


    Thanks and best regards,
    Niklas

  • 0 in reply to Niklas Schwarz
    Prodigy 10 points

    Hi Niklas,

    Yes, I'm using the newest revision (revision B) and I have a resistor of 30.1kΩ, so it is configurated to the output range of (15V-57V).

    I don't know if I have to configure another property related with the current or related with the simulation settings to get the correct output voltage because the error occurs when I have as RLoad=4Ω it doesn't occurs when I have as Rload=1kΩ.

    When I have Rload=1kΩ the output voltage reach the correct output voltage for example Vin=8.5V Vout=25V but changing the Rload to 4Ω I doesn't reach 25V, that's why I think is something related with current limits or simulation settings.

    Thanks!

    Regards, Emmanuel.

  • 0 in reply to Emmanuel Olvera
    TI__Mastermind 20510 points

    Hi Emmanuel,

    Thanks for the update.
    So the design works fine with light loads, but does not reach the target output voltage at higher loads?
    In this case, it might be a general design issue.
    For this, I would recommend to make a general design review.
    Could you please fill in the quickstart calculator for LM51231 and share your schematic?
    The calculator can be found here:
    https://www.ti.com/tool/download/SLVRBJ1

    Thanks and best regards,
    Niklas