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LM5175: No-Load Converter Heating

Tim Finks89
Prodigy 40 points
Part Number: LM5175

17-28 V in to 27.5 V out 4-switch buck-boost.

24 V in. 500 KHz. No load.

LM5175 has 40C temperature rise. Inductor is 2.2uH and shows a 25C rise (all converter parts are physically close and thermally coupled).

Temperature rise with no load is not acceptable.

What aspects of converter design choices or converter behavior might be the cause?

(Waveform measurements not yet available)

  • 0
    TI__Genius 11490 points

    Hi Tim,

    Difficult to say what could be the issue without seeing any thermal plots waveforms etc. I think the converter operation should be checked to make sure it is switching normally. For this SW1, SW2, Inductor current waveforms should be checked.

    2.2uH seems low for 27.5VOUT. 

    Regards

  • 0 in reply to Vijay86929
    Prodigy 40 points
    We have an earlier version of the design using a 3.3uH inductor, and the no-load heating is but a few degrees, if that.

    The 2.2uH value comes from the LM5175 data sheet Inductor Selection paragraph, where the buck and boost inductor alternatives are discussed. With the application values we have, the buck inductor was the largest, and was calculated near 2.2uH.

    Considering the symptoms (inductor core loss/heating), I suspect that 2.2uH is too small.

    Converter output behavior (steady-state, at first glance) is fine at 5A out.