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LM5122: VRIPPLE_MAX(CIN)

Kuramochi Tadahiko
Guru 28715 points
Part Number: LM5122

Hi,

My customer is considering using LM5122 and calculating Cin.

Does VRIPPLE_MAX(COUT) mean VIN ripple voltage?

If yes, why can it be calculated the equation (34)?

Best Regards,

Kuramochi

  • 0
    TI__Expert 7450 points

    Hi Kuramochi,

    This is based on the Vin=Vout/2 case.

    Inductor current ripple peak to zero: I_ripple=Vin*D/(2*L*fs)=Vin/(4*L*fs)

    Input cap voltage ripple peak to peak: dV= integrate(I*t)/C = 1/2*I_ripple*dt/C = 1/2*Vin/(4*L*fs)*1/2*Ts/C=1/16*Vin/(L*fs^2*C)=1/32*Vout/(L*C*fs^2)

    Please let me know if you have any questions.

    Thanks,

    Yinsong