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#### treez

##### Guest

As per page 32 of the attached….

“Switch Mode power converter compensation made easy “ by Robert Sheehan

….if you design an SMPS, and you compensate its feedback loop such that it is stable with an output capacitance of C1, say, then obviously it is stable.

Now add another capacitance to the output, call it C2…add C2 downstream of C1.

Now suppose that even with C2 added…the converter is still stable with good gain and phase margins..still stable without changing the compensation……

…Now add an inductor downstream of the output divider, and downstream of C1, but upstream of C2……. Now the SMPS could go unstable. (it will go unstable if the L_C2 resonant frequency is less than 3x the SMPS crossover frequency)

This is (to the simple minded like myself), not intuitively obvious…..

But page 32 of the attached confirms it.

..Now suppose we add a low value resistor instead of the inductor. Can you confirm that this will not go unstable?

“Switch Mode power converter compensation made easy “ by Robert Sheehan

….if you design an SMPS, and you compensate its feedback loop such that it is stable with an output capacitance of C1, say, then obviously it is stable.

Now add another capacitance to the output, call it C2…add C2 downstream of C1.

Now suppose that even with C2 added…the converter is still stable with good gain and phase margins..still stable without changing the compensation……

…Now add an inductor downstream of the output divider, and downstream of C1, but upstream of C2……. Now the SMPS could go unstable. (it will go unstable if the L_C2 resonant frequency is less than 3x the SMPS crossover frequency)

This is (to the simple minded like myself), not intuitively obvious…..

But page 32 of the attached confirms it.

..Now suppose we add a low value resistor instead of the inductor. Can you confirm that this will not go unstable?