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Original question:

LM5157-Q1: LM5157

LM5157-Q1: LM5157

RAYEES K E
Intellectual 270 points
Part Number: LM5157-Q1
Other Parts Discussed in Thread: LM5157

Tool/software:

Hi,

I am doing the AC Sweep simulation for LM5157 Sepic converter by using the Average model suggested by TI. 

I have connected the AC source in series with the FB line and try to do the Bode plot with trace expression "Bode plot dB-Seperate(V(Vout)/VACIN)). This will be across the AC source  (Vout is OUT side and VAC IN is other side of the AC source). But my results is not as expected. Whether i am doing the right methode? or any limitation to the LM5157 model to perform this kind of Simulation.

I have checked the Average model simulation provided by TI, but here the AC source is connected to GND through capacitor (Value 100Meg), also one high value 100Meg inductor added at the secondary. This is not the SEPIC i thing.

Can you help me by providing some details, how to perform the Bode plot analysis for SEPIC converter using LM5157 IC.

Regards

Rayees 

  • 0
    TI__Mastermind 25820 points

    Hi Rayees,

    Thanks for splitting the requests into separate threads. This will maintain a much better overview on each topic!

    Unfortunately, the average simulation model is designed for a Boost topology only. There is no average testbench available for a SEPIC topology and the Boost testbench cannot be changed to a SEPIC topology either.

    We have a LM5157 SEPIC evaluation board available.
    https://www.ti.com/tool/LM5157EVM-SEPIC
    This design comes with a full test report and bode plot measurement. This may be a helpful reference instead.

    Best regards,
    Niklas

  • 0 in reply to Niklas Schwarz
    Intellectual 270 points

    Hi Niklas,

    Thank you for your reply.

    So, with this model we cannot perform the AC Sweep/Noise analysis for SEPIC Design.

    Regards

    Rayees K.E

  • 0 in reply to RAYEES K E
    TI__Mastermind 25820 points

    Hi Rayees,

    Correct, it is not possible to use this model to perform AC analysis for SEPIC or Flyback designs.
    I am very sorry for this inconvenience.

    Best regards,
    Niklas