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LM3150: The output voltage of the LM3150 is too high under light load

强 王
Prodigy 125 points
Part Number: LM3150
Other Parts Discussed in Thread: LM61480, LM5146

  • I used LM3150 to make a power converter with 10-26V input and 5V 8A output voltage. However, the output voltage is 5.6V under no-load or light load. 

    When the load is greater than 2A, the output voltage is normal.

  • What might be the cause of this problem?  Thank you very much!
  • 0
    TI__Guru 60677 points

    Hello,

    Please forward the schematic and a completed quickstart calculator. Does the Iout range where Vout is higher correspond to DCM operation? If so, check the inductor ripple current, as it should be 30-40% of full-load current.

    Note we have the LM61480 36V/8A converter (with integrated FETs) that may provide an easier solution.

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    Prodigy 125 points

    • Thank you for your answer.

      Attached is my schematic diagram. Please check it. Thanks!

  • 0 in reply to 强 王
    TI__Guru 60677 points

    Hello,

    Apologies for the delay over the holiday period here in the US.

    Looking at your schematic, here are some comments:

    1. Paralleled FETs should not be required for an 8A load (just use 5 x 6mm FETs - see the LM5146 EVM as an example).
    2. 1.65Meg is a high resistance across the inductor, possible increasing noise pickup. Try lower R, higher C here for a lower impedance network. Check that the ripple ampltude is not too high as a COT regualtes on the valley of the ripple (this effect causes Vout to regulate higher at no load).
    3. Make sure the ceramic input caps are close to the FETs (see app note SNVA803 for layout detail/guidance).

    Regards,

    Tim