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ADS7800: Using MLCC instead of tantalum capacitors

Noriyuki Takahashi
Genius 9660 points
Part Number: ADS7800

Hi team

In the datasheet, it is recommended to use tantalum capacitors as below. But when they want to use MLCC, is it OK to use MLCC instead of tantalum capacitors. And what value of MLCC should be use for REF-pin & VS-pin, considering the DC bias characteristic?

1. Pin 3 (REF) should be bypassed with a 22µF to 47µF tantalum capacitor.

2. The VS pins (23 and 24) should be connected together and bypassed with a parallel combination of a 6.8µF tantalum capacitor and a 0.1µF ceramic capacitor located close to the converter to obtain noise-free operation.

Regards,

Noriyuki Takahashi

  • 0
    TI__Guru 62475 points

    Hello Takahashi-san,

    MLCC capacitors were less common when this product released which is likely why the recommendations are as they are.  Often REF outputs provide a better noise response with some small ESR in the load capacitor.  MLCC have much lower ESR than Tantalum caps so we'd recommend adding a small ~0.5 - 1Ω resistor in series with the MLCC capacitor for the reference pin to provide the same ESR effect the tantalum caps were providing.

    1.)  Use 22-47uF MLCC with small 0.5Ω - 1Ω in series to replace ESR of the tantalum.

    2.)  Replacements with similar valued MLCC capacitors is fine here.

  • 0 in reply to Collin Wells
    TI__Genius 9660 points

    Collin,

    Thanks! 

    Do you think that they need to consider  the DC bias characteristic, then decide the value of MLCC that can match with value of tantalum capacitor?

    Regards,

    Noriyuki Takahashi

  • 0 in reply to Noriyuki Takahashi
    TI__Guru 62475 points

    Hello,


    Yes, make sure they acquire MLCC capacitors that are at least rated to 2x, preferably 3x the highest applied voltage.  So, use 10V or 16V rated capacitors for a +5V signal net.  This will lower the impacts of the voltage coefficients of the capacitors.