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TPS546D24A: Number of paralleled input capacitors

Garret Holt
Intellectual 1050 points
Part Number: TPS546D24A

Hi Team,

I am working with a customer who is planning to use TPS546D24ARVFR for a design stepping from 12V (10.8-13.2V range) to 0.72V @30A. How many 10uF 35V X5R 1210 ceramic input capacitors would you recommend using? We have a 2.2nF and 1uF cap for high frequency filtering but it would help to know how many other caps should be paralleled in addition to the bulk capacitance. Is the primary contributor to the number of paralleled caps to be below the max ESR which can be calculated in the DS (8.2.2.5 equation 24)? Any other factors? Thanks for your help!


Regards,

Garret

  • 0
    TI__Genius 14455 points

    Hi Garret,

           The paralleling of caps effectively helps lower the net impedance in the frequency range of interest. As capacitors are not purely capacitive and tend to become inductive as frequency increases, the paralleling of multiple caps of different values, helps lower the impedance in specific frequency ranges.

    Paralleling the bulk caps helps with lowering the ripple  (contributed by the ESR, ESL and the capacitance) at the switching frequency. The high frequency caps 2.2nF and 1uF help with reduce switching spikes and serve as high frequency bypass caps.

    Here is a link to the WEBENCH design for reference. Please customize the design for your transient and ripple requirements.

    https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=F3AD0FEB988C4BD5

    Regards,

    Gerold