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TPS54160A Equation(48)

Kuramochi Tadahiko
Guru 28715 points
Other Parts Discussed in Thread: TPS54260

Hi,

I guess that the equation (51) in the D/S is wrong.

Firstly, when  the equation (48) in the D/S is changed, it becomes "GMOD(fc)*gm(EA)*Rc=Vout/Vref".

I'm thinking that this equation is to calculate Rc as the modulator voltage gain x the error amp voltage gain = Vout/ VREF.

And, I'm thinking the units the left-hand side and right-hand side are [V/V].

On the other side, 

when  the equation (51) in the D/S is changed, it becomes "GMOD(fc)*gm(EA)*Rc*fz(mod)=Vout/Vref".

I cannot understand multiplying "fz(mod)".

And, I'm thinking the unit of the left-hand side is [Hz*V/V], right-hand side is [V/V].

I think that this is and error.

And, when I check the D/S of TPS54260, a equation calculating RC is only 1(it isn't divided Low ESR and high ESR).

So, I think that the equation is wrong.

Could you advise me ?

Thanks and Regards,

Kuramochi

  • 0
    TI__Guru**** 191445 points
    I am not sure where those equations came from. Yo are certainly correct that the units do not work out for EQ 51, but I think it is just an approximation anyway.
  • 0 in reply to JohnTucker
    Guru 28715 points
    John-san,

    I have the other question.
    I calculated values on based the equation (48)~(50) for the typical application of the D/S.
    The result is following;
    - Rc=3.3/(0.542*97u*0.8)=78.46kΩ(76.2kΩ)
    - Cc=1/(2π*78.46kΩ*1.5kHz)=1352pF(2710pF)
    - Cf=47uF*50mΩ/78.46kΩ=3.0pF(6.17pF)
    ※The values inside the parentheses are the result of the D/S.

    I think that the equations are correct and the results of the D/S are wrong.
    Because, purpose of the pole and the zero for phase compensation is to cancel fp(mod) and fz(mod) .

    Thanks and Regards,
    Kuramochi