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Original question:

LM5166: Problem with Ceramic caps making sound

LM5166: Problem with Ceramic caps making sound

Per Fager
Intellectual 390 points
Part Number: LM5166

So i have two questions to you:

1) can we use this polarized aluminum capacitor?

2) What shall use on C3.

The board will have components on only one side so i can not use the sound cancelation method by placing half of the value on each side.

Best Regards

Per Fager

  • 0
    TI__Mastermind 27045 points

    Hi Per,

    Do you check circuit design of LM5166EVM-C33A ?

    C9 require big enough ESR for proper output ripple, pls try it with 0.11ohm in series ceramic cap C9 as design on EVM.  otherwise loop maybe unstable and cause audible noise.  C24 should be electrolytic cap with big ESR. The ceramic cap C3 should not generate audible noise as input voltage is stable.  

    Pls pay more attention on L1, pls use molded inductor ( like iron powder core inductor) which helps lot to reduce audible noise.

  • 0 in reply to Andy Chen
    Intellectual 390 points

    Hi Andy 

    Thanks for the answer!

    Yes i have LM5166EVM-C33A as reference. 

    I will focus on L1.

    Add ESR resistor 0.11ohm before C9

    Go back to ceramic 47u/10V X7R on C9

    Change to COT mode because the sound is almost gone in this mode.

    See attached schematics of my DC/DC connection below.

    I have used Coilcraft LPS6235-473MR thought this one was moulded.

    /Per

    So should i test the other two suggested in the BOM of LM5166EVM-C33A?:

    Würth 74404063470

    TDK CLF6045NIT-470M-D

    Are they more silent?

  • 0 in reply to Per Fager
    TI__Mastermind 27045 points

    Hi Per,

    Würth 74404063470 should has lowest noise since the winding surround by glue. 

    Coilcraft LPS6235-473MR and TDK CLF6045NIT-470M-D should have similar structure, you can compare their noise level with Wurth part.

  • 0 in reply to Andy Chen
    Intellectual 390 points

    Hi Andy

    I got the Würth coil last week and today i had time to test it. The module i have run in PFM mode. Difficult to switch to COT because of the layout and missing resistor to pin 5. GND directly.

    In this PFM mode it was silence also runned the test with ESR of 0.2ohm to the C9.

    Thanks for this information it seems to help really good!

    We will in the Product switch to this Würth coil instead.

    The issue i resolved for now.

    BR

    Per Fager