A buck pulse-width modulated zero-current switching quasi-resonant converter operating at constant frequency is discussed. The converter is modeled using the piecewise-linear approach in order to formulate more compact and more exact expressions. The digital-PWM controller is based on the FPIC technique (or Fixed-Point Inducting Control), that it was proposed, recently. This technique has been only reported in hard-switching converters. The properties of FPIC in softswitching topology are investigated. Real-time and delayed performances are shown.