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LM5155: Low efficiency compared to theory calculation

Garrick Dai
Intellectual 1660 points
Part Number: LM5155

Dears,

My customer used LM5155 for boost -- input 7.2V, output 24. Below is circuit and layout. Customer actual test efficiency is only 85%, big gap compared to theory calculation as high as 95%.Please help check.

  • 0
    TI__Mastermind 20900 points

    Hi Garrick,

    efficiency is impacted by a lot of factors (inductor, switching frequency, FET, diode, output current, input voltage ...). 

    Do you have a BOM list to look at? 

    And what is the output current?

    At low input voltage and high output current the efficiency is expected to drop to a certain extent (see Figure 10-2 in the datasheet).

    Also, could you please let me know, what is the theory calculation based on?

    regards,

    Julian

  • 0 in reply to Julian Hagedorn
    TI__Intellectual 1660 points

    Hi Julian,

    Added customer test below. Will check the BOM.

    1, Output 1.5A(23.57V), and input power 41.544W(7.2V*5.77A), so eff. = 85.1%

    2, Output 0.1A(23.77V), and input power 2.715W(7.2V*0.377A), so eff. = 87.6%.

    From the test above, it seems light load(0.1A) efficiency is little higher than heavy load(1.5A), which is different to spec.

    BTW, the theory calculation tool is LM5155 Boost Controller Quick Start Calculator