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LM25118-Q1: the selection for the parts

Part Number: LM25118-Q1
Other Parts Discussed in Thread: LM25118

Hello Team !

I have been studying your product LM25118.LM25118.xlsx

Now I have a question about the selection for current sensing resistor.  (see the attached excel file)

I have to consider the the Buck Mode Peak inductor current and the Buck-Boost Mode Peak inductor current ?

Because I am afraid the power resistance. The peak current is so large.

Next, about the inductor L

 I must consider the Buck Mode Peak inductor current and the Buck-Boost Mode Peak inductor current ?

The peak current is so large (especially the Buck-Boost Mode    more than 11A ).

I think the peak current is not steady, is it correct ?

Best Regards,

Yukitoshi Takemura

  • Hi Yukitoshi,

    Thank you for using E2E forums, could you please elaborate on what is your question? the peak current of the inductor depends on the Vin and usually it is a triangular waveform.

    I might have misunderstood your question, could you please ask me what is the specific question that you are asking?

    Thank you 

    BR,

    Haroon

  • Hi Haroon-san,

    Thank you for your response.

    I am very sorry for my poor English and my poor explanation.

    I would like to make two questions below.

    1. about the Rs (current sensing resistor) selection

      I set the Vinput= between 8V and 32V,Vout=12V, Iout=3.6A(MAX)

    (The circuit schematic has already showed by last letter.)

      I have estimated some value (Rs .......)  by your Tool. I have decided the Rs value 

     is 20mohm.   I believe the L current other than Iout.

     The L current is so large, so I am afraid the power consumption at Rs.

     I must select the proper power loss of Rs       

    2. about the L(inductor) selection

     I have decided the L value is 15uH.

     As mentioned above the L current is so large.

     I must select the L in consideration of not only Iout but L current ?

    Best Regards,

    Yukitoshi Takemura   

  • Hi Yukitoshi-san,

    Thank you for elaborating, regarding your questions:

    The inductor current might rise to 11A when the Vin is at the minimum so that might cause some considerable amount of losses at the Rs resistor. you could decrease the Rs and the inductor value but due to the high output current your inductor current especially at the Vin minimum will be quite high and that will have some effect on the power losses of your system.

    BR,

    Haroon

  • Hello Yukitoshi-san,

    I have not seen an update from you for the last 22 days, so I assume the questions are answered and the issue is solved.
    I close this thread now. If there is still something open, please reply and the thread will get opened again.
    If you have any other question or of the thread has been locked, please open a new one.

    Clicking the Resolved Button also helps us to maintain this forum.

    Best regards,
    Harry