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Buck DCDC Cout power consumption in pulse skip eco-mode

K. Sasaki14
Guru 10200 points

Is there calculation method of Cout power consumption in pulse skip eco-mode?

Do we have to measure ripple current and calculate RMS current?

Best Regards,
Kohei Sasaki

  • 0
    TI__Guru**** 191445 points
    I have not really considered this before, but the maximum RMS current should occur in CCM, not eco-mode. If you size the output capacitors for CCM, then you should not have any issue in eco-mode.
  • 0
    TI__Mastermind 25590 points

    I'll add to what John said. If you're looking to calculate the power dissipated by the Cout capacitor itself, and the pulses are sufficiently infrequent, the power loss should be on the order of ESR*(2*Iout)^2 for a single output capacitor. Adding more caps makes this more complex. As the pulses get more frequent, this equation starts over-estimating the power loss.

    I got this by figuring that, with our assumptions, the current from the switch pulse will go through the ESR of the cap to charge the cap, then while SW is off, it has to come out through that ESR again (hence the "2" in the equation). The rest is just P=RI^2.

    Any other effects should be negligible. In fact, this current itself should be negligible. 10mA at 10mOhmESR would get you no more than 4uW.

    -Sam