Critical Parameters in the Transient Response of Synchronous Buck Converters

The transient behavior of synchronous buck converters, using critical parameters, is investigated in this work under high current slew-rate load transients. Critical parameters are defined as the combination of parameters for which the peak transient response is dominated by the effect of the capacitor Equivalent Series Resistance (
ESR
). Given the importance of the effect of
ESR
in low-voltage, high- current synchronous buck converters, an effective normalization method is developed in this paper to reduce the dependence on other parameters, thus providing valuable generality to the transient analysis. A set of critical normalized expressions valid for any possible synchronous buck converter is derived, which can be used as a useful design tool to meet transient specifications. By using critical parameters, both transient recovery time and peak voltage regulation can be met while keeping
L
and
C
to a minimum. A detailed characterization of the effect of
ESR
is presented, and the normalized approach clarifies the role of
ESR
in the transient response. A critical design example is presented where the parameters of the converter are obtained by performing a simple denormalization. Finally, the critically designed converter is evaluated using boundary controllers as well as classical current- and voltage-mode controllers to assess the influence of the control scheme on the transient response of the converter.