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LM5576-Q1: Use of Ceramic Output Capacitors

David Sackmann
Prodigy 20 points
Part Number: LM5576-Q1

Is there a reason ceramic output capacitors can not be used in place of tantalum in this design https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=DC77A6550DE6D435

  • 0
    TI__Genius 17075 points

    Hi David,

    Thank you for your question. Per the datasheet, the recommendation on page 14 of the datasheet is to use a ceramic capacitor to reduce ESR and an SP organic capacitor in parallel for large bulk capacitance for transient loading conditions. I have included the excerpt for your convenience:

    Thus the webench designer for this part has both the tantalum (Cout) and ceramic (Coutx) in parallel. These both are available for modification to your design's needs. You can also create a custom design for a part to simulate the characteristics of the passive component that you wish to add.

    Thank you,

    Joshua Austria

  • 0 in reply to Joshua Austria
    Prodigy 20 points

    Hi Joshua,

    We would like to substitute four Taiyo Yuden UMK325BJ106KMHP 10uFd 50V pats for the three Panasonic 25TQC15MYFB 15uFd 25V parts for the Cout bulk capacitors in the Webench design.  The ceramic part is already used in other circuits on our board and has a smaller footprint.  What should we be aware of when making this change?

    Thanks,

    Dave S

  • 0 in reply to David Sackmann
    TI__Genius 17075 points

    Hi David,

    Thank you for your question. Apart from having different package sizes, the Taiyo Yuden has a more limited operating temperature (-55~85 C) than the Panasonic parts (-55~105 C). You are also working will less output capacitance, but with a higher voltage rating, as long as your application is rated to work with this effective output capacitance, you should be ok. 

    I also noticed that this part is marked for "not for new designs" but if you are already using these parts, then I am assuming this is ok as well.

    Thank you,

    Joshua Austria

  • 0 in reply to Joshua Austria
    Prodigy 20 points

    Joshua,

    What criteria should we be using to determine if our application is rated to work with the effective output capacitance?

    Is there a reason that Webench only lists tantalum parts for possible Cout alternatives?

    We have other 10uFd 50V ceramic capacitors besides the Taiyo Yuden part on our approved vendor list so availability should not be an issue.

    Thanks,

    Dave S

  • 0 in reply to David Sackmann
    TI__Genius 17075 points

    Hi David,

    Thank you for your questions.

    The main consideration for output capacitance is desired output voltage ripple and stability.

    Please see equations 15 thru 16 of the datasheet for more details on stability and this excerpt below for output voltage ripple that I have included for your convenience:

    As for your other questions, please refer to the first response.

    Thank you,

    Joshua Austria