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TPS54308: Calculation for cross over frequency

tetsuro yamaji
Prodigy 20 points
Part Number: TPS54308

Dear TI Power management team,

On datasheet TPS54308 Equation 14,

Cross over frequency is related with only Vout and Co.

But I think it should be related with load current Iout also.

I think below.

- Iout is related 1st pole frequency.

  fpole = 1/ (2*PI*Cout*Rout) , Rout = Vout / Iout

- Over all open-loop gain at low frequency is not related Iout.

- If decrease Iout(light load condition), Rout increase and fpole decrease,

  And then cross over frequency isdecrease

Would you correct my mis-understanding?

Best regards,

Yamaji

  • Former Member
    0 Former Member

    Hi Yamaji,

    The overall DC gain is related to Iout.

    If decrease Iout, Rload increase so that DC gain increase while fpole decrease. The crossover frequency keeps no change then.

  • 0 in reply to Former Member
    Prodigy 20 points

    Dear Mr. Bruce

    Thank you for your quick reply.

    I understood below.

     Current-mode power stage seems to be current source.

     Current source gain is related RL(Rout)

     RL related Iout

     If decrease Iout(light load condition), Rout increase and fpole decrease, but Gain increase, 

    As the result can keep cross over frequency.