Tool/software: WEBENCH® Design Tools
Hi team,
I have query related to Phase margin calculation and I am using Switcher Pro tool and tsp54521 buck converter.
According to the tps54521 datasheet i have calculated poles and zeros frequency at 70Khz crossfrequency and also calculated the Phase margin but when i run the stimulation on switcher pro phase margin doesn't match the theoritically calculated value.
So I tried to calculating in the reverse way i.e I ran the default stimulation for tps54521 on switcher pro (picture of result is attached at the bottom of the query) and got PM of 77deg.
Taking the value from the default stimulated schematic i.e crossover freq Fc= 40.9Khz, C6 = 390pF, C4 = 1.8nF, R4 = 3Kohms, Cout=104.7uF and Resr=0.002ohms
And calculated the Poles and Zero freqeuncies which are Fp1=37.168 hz, Fp2= 136.1 Khz and Fz1= 29.48 Khz and then calculated Phase Margin at Fc= 40.9Khz using the following equation
Phase margin = 180 - tan^-1(Fc/Fp1) - tan^-1(Fc/Fp2) + tan^-1(Fc/Fz1)
I got Phase margin of 127.5 deg which is not even nearby of 77 deg.
I tried a lot by not getting the required answer can you please explain me what am i doing wrong or Am i missing something in calculating the value.
Thank you.
