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TPSM8287A12: CLOAD of effective capacitance

Yuta Nishie
Genius 3655 points
Part Number: TPSM8287A12

Tool/software:

Hi,

Please tell me how to calculate the effective capacitance value of CLOAD =about 138 μF described in the datasheet "9.2.2.4 Selecting the Output Capacitors."

According to the DC bias characteristic of Murata's CLOAD (GRM32 EC80G227ME05L), the capacitance value decreases by 6.2% when VOUT=0.9V(Table 9-2. Design Parameters). Therefore, I think 220×0.938=206.36uF. Since it is not 138uF, please tell me how to calculate it.

Best Regards,

Nishie

  • +1
    TI__Expert 3808 points

    Hello Nishie,

    this worst case number also considers thermal impact and the capacitance variance of +-20%.

    Assuming 20% degradation from both you get: 220μF * 0.8 * 0.8 * 0.938 = 132μF which is close to the datasheet listed value. So I assume they used a slightly different value at some point.

    I hope this clarifies your question.

    Regards, Werner