Ripple-based prediction of fast-scale instabilities in current mode controlled switching converters

In this paper a closed-form stability condition is obtained for predicting the boundary of fast-scale instability in a buck switching power converter. This design-oriented condition is obtained from the discrete-time model and it is validated by means of numerical simulation under different cases, including only the voltage-mode loop, current-mode along with voltage-mode loop open or closed, or adding an external compensating ramp. The availability of such design-oriented expression allows to understand the effect of the different parameters of the regulator upon the stability boundary along with facilitating the design and synthesis of new controllers to avoid these instabilities.