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TPS54620 - Derivation of R4 equation

Mike Ulrich
Expert 3110 points

Hi,

How is the equation for R4 in the datasheet derived?

Thank You,

Mike Ulrich

  • 0
    TI__Guru**** 191445 points
    I'm not sure. I do not use that equation myself. As you probably know there are many different valid ways to design compensation. I am pretty sure the person that came up with that is no longer around. I can probably reverse engineer the math (easy enough) and then make a guess as to what they were thinking.
  • 0 in reply to JohnTucker
    TI__Guru**** 191445 points
    Assuming crossover occurs after the compensation zero and before the compensation pole, (gain of compensated error amp at Fco) = gmea * Rcomp * Vref / Vout. By definition this gain is equal and opposite of the power stage gain at the same frequency. Substituting, it assumes the gain is 2*pi*Fco*Cout/GMPS. This is just simple ideal current mode control with no slope compensation.