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TPSM82810: Effective output capacitance limit

Danilo A.
Mastermind 26510 points
Part Number: TPSM82810

Hi Team,

We have received this inquiry from our customer.

Looking through the datasheet of TPSM8281x (as well as other voltage converters), there is typically a recommended effective output capacitance range provided. For the TPSM8281x this range is 27uF (min) to 470uF (max). What is meant by or included in this effective output capacitance limit? Does this capacitance include all capacitive loads on the output voltage rail and subsequent secondary voltage rails? 

For example: 

TPSM8281x effective output capacitance = C2 + C3 + [C4*(3V)^2]/(5V)^2, is this correct? 

C4 is scaled from the 3V to the 5V rail using the capacitor energy formula (E=CV^2). Is this a valid method to scale the output capacitance of a converter or LDO to the input side? Or should this scaling be done using the capacitor charge formula (Q=CV)?

Regards,

Danilo

  • 0
    TI__Genius 16930 points

    Hi Danilo,

    The output capacitance of the TPSM8281x only refers to the output capacitance on it's output rail and not the subsequent secondary voltage rails. In the example you showed, it would only be the capacitance on the 5V rail, i.e. COUT= C2+C3.

    Due to the DC bias effect of ceramic capacitors, the effective capacitance is lower than the nominal value when a voltage is applied. Please check the manufacturer´s DC bias curves for the effective capacitance vs DC voltage applied. 

    Best regards,

    Varun