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LM25118: Inductor selection

Nidhi P Shetty
Intellectual 735 points
Part Number: LM25118
Other Parts Discussed in Thread: LM5118

Hello

I'm using LM25118 in my project. I'm providing 9-30V input and output is 30.5V at 2A. Iripplemax= 0.9A f=294.6599KHz

In datasheet for inductor selection formula for buck mode if I use i will get -1.88270349802606E-06H and for buck boost mode i will get 25.7382250363057E-06H. How to choose inductor for this case.


Please help me out in this concern.

Regards

Nidhi P Shetty

  • 0
    TI__Guru* 78270 points
    Hi Nidhi,

    First, you should use the design tool at www.ti.com/.../snvu065 to help you design.

    There is always a trade-off in selecting a part, and most trade-off are based on cost-performance. In your case, your Vin_max is <Vout, so the buck calculation is not applicable. You just select the inductor by the buck-boost calculation.

    Thanks,
    Youhao Xi, Applications Engineering
  • 0 in reply to Youhao Xi
    Intellectual 735 points

    Hello

    Thank you for sharing the document.

    Can you give me a clarification that whether the calculation that you have provided remains same for LM25118 as well. Because you have provided it for LM5118.

    Please help me out in this concern.

    Regards

    Nidhi P Shetty

  • 0 in reply to Youhao Xi
    Intellectual 735 points
    Hello
    In the document you shared selected bandwidth is assumed on what basis?
    For system stability what should be the gain margin value if gain margin is negative?
    Whether gain margin is to be more negative? or less negative?
    For example whether system with -22db gain margin is more stable or one with -55db is more stable?
    Please help me out in this concern.
    Regards
    Nidhi P Shetty
  • 0 in reply to Nidhi P Shetty
    TI__Guru* 78270 points
    Hi Nidhi,

    As I mentioned, being stable is being stable, there is no concept of being more stable with a gain margin of -55db vs -22db. The bandwidth was chosen to be reasonably appropriated for the targeted applications, such that the dynamic response meets spec.

    Thanks,
    Youhao