SMPS stability with Current_mode vs Voltage_mode control

[cupoftea]

Hi,
When you have a current mode converter and its unstable. You can often make it stable by reducing the feedback loop crossover frequency.

With a voltage mode converter, there is the power stage output LC filter, and its 2 poles to think of. As such, this rule of “reducing the crossover frequency in order to get stability”, doesn’t work any more.
Also, supposing, with a voltage mode converter, that you are crossing over at the output LC resonant frequency, and then you reduce feedback loop bandwidth from there……you will indeed be likely to get more stability, but your feedback loop will then be so sluggish that load/line transients may well present serious problems.

Would you agree?

 

[Easy peasy]

What is the phase delay of the LC filter at resonance ? ( volt mode ) how much phase delay does that allow you for the rest of the loop?

One can always use an RC filter before the L and regulate off that - a lot faster than out side the LC filter

one can also then add a slow damped loop with limited pull range from the output to bring the Vout to exactly required.