# Relationship between switching frequency and controller's crossover frequency in buck SMPS

Context: tuning the control loop of a buck SMPS. I specicifally have a TI TPS40200-based circuit in mind, but I think this applies to SMPS design in general.

Quoting from Type 2 compensation network:

Mr. Maniktala suggests that the loop gain transfer function of the switcher intersect
the 0 dB point at approximately 1/6th the switching frequency, with a slope of -1.


I have heard this before from another engineer, but did not get a chance to ask why. What is the reason the crossover frequency of the control network should be a fraction of the switching frequency? Why specifically around 1/5th or 1/6th?

Are there any other desirable traits when designing a compensation network for an SMPS controller other than the most basic criterion of >45 degree phase margin for system stability?