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TPS7A88: Input and Output Capacitors Requirements

Sanel Hirkic
Intellectual 1160 points
Part Number: TPS7A88
In the TPS7A88 datasheet, there's a statement "A ceramic capacitor with a value of 5 μF or larger (10 μF or greater of effective capacitance)" is recommended for the input/output capacitors. Is there a separate threshold for capacitance after accounting for tolerance/temperature/DC bias effects?
  • 0
    TI__Mastermind 34165 points

    Hi Sanel,

    AC bias has a big impact on the effective capacitance for ceramic capacitors, especially for an output capacitor.  Most capacitors are specified with a 1Vrms or 0.5Vrms AC voltage applied, usually at some frequency such as 1kHz.  The LDO will not have an AC ripple on the output so the effective capacitance can decrease by 10's of percentage points.  Not every manufacturer gives you data on the effective capacitance when a very small AC ripple is applied.  Murata does have this information, I'm unsure on the other capacitor manufacturers.

    Environmental conditions (if applicable) will also affect the capacitor tolerance.  The capacitor datasheet will usually list environmental conditions and how the capacitor changes with these conditions. 

    For these reasons we usually recommend selecting a capacitor that is 2x larger than the minimum effective capacitance to ensure you meet the datasheet requirements.  Selecting a 10uF capacitor here is a good idea (X5R or X7R depending on your temperature requirements).

    Thanks,

    Stephen