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TPS53667EVM-769: input capacitor and filter

Part Number: TPS53667EVM-769
Other Parts Discussed in Thread: TPS53667

TPS53667EVM has two 270uF OS-CONs and 65nH filter on input stage.

Must we put these components? Or does this depend on system requirement or input voltage quality?

Is there any concern that we use only ceramic capacitor for input capacitor?

Best Regards,
Kohei Sasaki

  • Hi Kohei,

    Typically the input filter caps for a high-current buck regulator like the TPS53667 are a mix of bulk caps like the 270uF ones on the ECM and ceramic caps as well. The ceramic caps handle the input RMS current requirements, keep VIN within tolerance during steady state, and are placed close to each power stage. Larger bulk caps hold up the input rail during large load step transients and provide a boost of current to improve VOUT transient response.

    Without knowing your design specs I can't say for sure if you can get away without a bulk capacitor or two. You can use the app notes below to learn more about designing with multiphase regulators and sizing the capacitors appropriately.

    Feel free to let me know if you have any other questions.


  • Carmen-san,

    Thank you for your reply.
    I have already seen your app note.
    Our customer design spec is the following,
    Vin: 12V
    Vout: 0.6V
    Iout: 120A
    They are going to use TPS53667 and CSD95490 with 500kHz Fsw and 5 phase condition.

    Could we use all ceramic input capacitor if put many parallel capacitors instead of large capacitance bulk cap?

    And please let me know if you have any concern about thermal performance and duty limit.

    Best Regards,
    Kohei Sasaki
  • Hi Kohei,

    Is there a reason the customer does not want to use bulk capacitors? Are they under some height restriction?

    If a sufficient amount of MLCCs were used, over the amount needed for the DC ripple and RMS currents, you could get away with not using bulk caps and still keep VIN within the tolerance during transient events. However, I'm not sure you would benefit much from a cost perspective or in regards to PCB layout area.

    Bulk caps do not derate with a DC bias applied and so extra ceramics would be needed, in 0805 packages or larger, to make up for this effect. While large, >100uF ceramics can be purchased they are costly and adding several to the board would probably cost as much as a bulk cap or two.