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LM5175-Q1: Please help to advise input capacitance

Part Number: LM5175-Q1

Hi Sir,

The operation condition is 6V-20V input, 8.5V output, 2.1A output current.

Current design is 68uF(POSCAP) and 3*10uF/1206/35V MLCC in input side.

Please help to suggest if it's ok to replace input 68uF POSCAP to the 7*10uF MLCC?

Thank you.

  • Hi,

    I would recommend keeping the footprint for the POSCAP on the design, but you can populate it as needed. If you were to add in more MLCCs, please keep in mind with MLCC's there will be a capacitance de-rating based on the voltage bias. 

    Thanks,

    Richard

  • Hi Richard,

    Because there is layout space consideration, customer can't reserve POSCAP location.

    Could we suggest them to put the MLCC capacitance but need to consider DC bias? 

    Thanks.

  • Hi user,

    If that is the case, I would recommend putting the MLCC capacitance on the board, but have one of the capacitors be in series with a damping resistor. Yes, also tell them to consider DC bias.

    The resistor can be populated as 0-ohm if not needed, but it will be good to have. If there is insignificant damping, you may find that during a load step, oscillations may occur due to the resonance between the parasitic inductance and capacitance; and may destabilize the dc/dc converter. 

    Thanks,

    Richard