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LM5176: schematic check

GARETH OU
Guru 11375 points
Part Number: LM5176

Hi

Could you help check below the LM5176 schematic and any need to adjust ,Thanks

8267.LM5176.pdf

  • 0
    TI__Mastermind 30030 points

    Hi Gareth,

    Thanks for using the e2e forum.
    I had a look the their schematic.

    They are only using ceramic caps and input and output. To compensate for stronger load steps and reduce voltage ripple, they can consider adding electrolytic bulk capacitance.
    They might also need to recalculate the compensation network, as I see very low phase margin in their current design.
    For this, they can use our quickstart calculator:
    https://www.ti.com/tool/download/SNVC208

    Their inductor is rated for 26A. For worst case conditions (min Vin, max load), the inductor will likely fall into saturation.
    Please consider an inductor with higher current capability.

    Best regards,
    Niklas

  • 0 in reply to Niklas Schwarz
    Guru 11375 points

    Hi Niklas

    1. Attached excel file is with the updated schematic. The phase margin is above 68 degree with 9~36V input.
          Please help check if anything else is needed to be modified.
      2. We put MLCC on input/output, because PCB size is limited.
          Would you think it is better to exchange MLCC to bulk?(e.g. 2xMLCC to 1xBulk)  
          If so, would you advise how should we modify it?
      3. Regarding the inductor, 20A output is a maximum estimated value. I think the real case should be less than that.
          So we consider to keep the inductor, and see the test result of prototype.

    LM5176 1226.xlsm

  • 0 in reply to GARETH OU
    TI__Mastermind 22650 points

    Hi Gareth,

    1.I think the design calculator is OK. Maybe you should use 60V MOSFET for 36V input and 30V MOSFET for 12V output. And 60V for D58.

    And where is SW1 and SW2 connected to?

    2.I think the input cap and output cap are not large enough especially considering DC bias characters.

    Typically, the input cap and output cap have more relation with the system requirements.

    For the output cap, we should consider the output ripple voltage and load transient. Please refer to:

    Basic Calculation of a Boost Converter's Power Stage

    How to determine bandwidth from the transient-response measurement

    Generally, we should use both low ESR ceramic capacitors and bulk capacitors for the output.

     For the input cap, we should consider the input voltage ripple and the stability as part of the input filter. Please refer to

    Basic Calculation of a Boost Converter's Power Stage

    Input Filter Design for Switching Power Supplies

    Generally, aluminum electrolytic capacitor is a good choice for input cap considering damping.

    Best Regards,

    Feng Ji