The datasheet for the TPS54060 (http://www.ti.com/litv/pdf/slvs919a) provides equations for minimum output capacitance (equation 34), and an equation for maximum capacitor ESR (equation 35). While following along with circuit example given in datasheet; I get different results for these two values. However, I cannot determine what I did wrong.
equation 34 : Cout > 1/(8*f_SW)*I_ripple/VO_ripple
equation 35 : R_ESR < VO_ripple/I_ripple
The text states the f_SW is 500kHz.
From what I can determine from previous results is that I_ripple should be (0.126 Amps). This is backed up by equation 31 which stats that:
I_peak = I_out + I_ripple/2
The text uses I_out = 0.5A and says the I_peak = 0.563A. If I_ripple is 0.126A then this equation works out. An I_ripple of 0.126A also matches my calculations.
However, for equation 34&35, I get 1/4 the capacitance and 4x the ESR the datasheet calculates
VO_ripple = 4% * 3.3V = 0.132V
Cout > 1/(8*f_SW)*I_ripple/VO_ripple = 1/(8*500e3)*(0.126A/0.132V)*1e6uF/F = 0.2386uF (the datasheet says 1uF)
R_ESR < VO_ripple/I_ripple = 0.132V/0.126Amps = 1.04ohms (the datasheet says 248mOhms)
I could assume that VO_ripple is a peak-to-peak value (+/-4%) and should actually be twice the calculated value, but this would make the result even farther off.
I can't figure out where the datasheet provided values come from, especially for R_ESR which is a pretty straight forward calculation.
