Buck converter LC output filter contribution to phase margin

I'm trying to develop a better understanding of how my power distribution network can affect the stability and performance of buck converters, which has lead me to documents like this one.

The main point of the document is pretty obvious, and I think I understand it: if the total phase response of the control loop is -180 degrees when the gain is >= 0dB, the regulator will probably become unstable. This matters to my design process because the LC output filter contributes to the control loop's phase response, and my power decoupling network contributes to the LC output filter.

My question: After running a few simulations, it looks like any reasonable LC output filter for my application will have a phase response of -180 at a pretty low frequency. Is my LC output filter having a phase response of -180 an automatic showstopper for a buck regulator, or would you expect a "modern" buck regulator to have enough internal compensation in its error amplifier to handle this issue?

This is my super low-resolution model of my LC output filter. I've included about 2nH / square parasitic inductance for my power plane as well as some roughly fudged ESL numbers for the decoupling caps, and a 50 ohm resistor for my low power microcontroller.

And here is a frequency sweep that goes from 1kHz to about 250MHz

• Have you found the transfer function of the DC to DC converter? it has feedback and there are ways to calculate it. You would need to find this first, then substitute this complex load instead of a regular restive load in your model . Commented Jul 19, 2019 at 21:35
• When the output cap has ESR the phase response goes to 90 instead of 180 .This makes control Stability easier . Commented Jul 19, 2019 at 22:34
• @VoltageSpike I have not. I am currently trying to find a good converter from Digikey, and I don't have the time to buy many converters and characterize all of them. Honestly, I'm not sure how I would go about finding the transfer function. Would I attach a filter with known phase response and then look at how the buck converter behaves as part of that loop? Commented Jul 19, 2019 at 22:54
• @Autistic Thanks for the advice! Is it a common design practice to put a low-value resistor (like, 50mOhm) in line with the capacitor in case the ESR is too low? Commented Jul 19, 2019 at 22:58