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Input bypass or bulk capacitors?

Barneymc
Prodigy 20 points
Other Parts Discussed in Thread: TPS5420

When I design a circuit using the TPS5420, I get C1 with an "OPEN" value and C9 with a value of 3.3uFd. When I look at the Layout view, it tells me I typically need a 10uFd bypass capacitor. In the spec sheet, it says I need bypass capacitance and sometimes also need a bulk input capacitor.  My question is, do I need to add 10uFd input bypass capacitance? Is the recommended 3.3uFd considered the bulk or the bypass capacitor?  What is the total required for bulk and bypass?

Thanks - Barney

 

  • TI__Mastermind 26205 points

    Barney

    Sorry for taking so long, we are addressing this and will return to you soon.

    regards

    rogerio

  • TI__Intellectual 2710 points

    Hi Barneymc,

    Typically some input capacitance is needed.  3.3uF is the calculated recommended value.  The layout guidelines are text from the datasheet, and not specific to the SwitcherPro input.  10uF is a good default recommendation.  

    Whether you need more bulk cap or input cap is more dependent on the supply characteristics and distance from Vin than the TPS5420 itself.

    Thanks,

    Hetal Joshi

    Senior Developer and Project Manager

    Analog eLab Design Center

    HPA Design Tools

    Texas Instruments, Inc.