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LM5157-Q1: Design review support

Part Number: LM5157-Q1
Other Parts Discussed in Thread: LM5157

Hi TI experts,

Please support to review the design in attachment file with following specs:

Input: 6-20V

Output: 23V- 0.2A max => supply for gate driver , that why i chosen not boost but flyback

Parameters and Component part nos as in schematic. 

I’m looking forward to receiving your feedback. Any suggestions will be greatly appreciated



  • Hi Tuong,

    Thanks for using the e2e forum and providing the application specs.

    From the schematic file, it looks like there is just the power stage modeled and the circuit around the IC is strongly simplified. (The converter only has pins for drain, source, FB and BP)
    Would it be possible to share the full converter schematic including all LM5157 pin connections?
    This would be necessary for a review of switching frequency, softstart/UVLO implementation, compensation, etc.

    I also received your request for the unencrypted LM5157 PSpice model files.
    The model files will be forwarded to you shortly through another communication channel.

    Thanks and best regards,

  • Hi Niklas,

    Sorry my bad. I was upload the wrong file. New file was reup.

    I received your pspice model as well. Thank you.

  • Hi Tuong,

    Thanks for the update
    Overall, the schematic looks good to me.
    The pin connections are all correct and the layout notes are good as well.
    The one thing I can point out is that the inductance of 5uH is rather small for this application, which leads to a stronger current ripple that might lead to a visible voltage ripple of the output voltage.
    The system should run completely stable with the current values, but if you observe larger ripple of VOUT, you can consider adding more output capacitance.

    You can double check all these values and the compensation with our quickstart calculation tool:

    Best regards,

  • Hi Niklas,

    Thank you for valueable feedback. 

    I used the tool to check compensation as below graph.

    I recieved your model and simulate with LTspice (sorry i am LTspice fanboy) but no pulse in SW pin. Could u please take a look? I can send the simulation file.

    Looking for your comment.