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The nonlinear and linear controls proposed by Alou and Soto provide very fast transient response (voltage step from 1 to 1.5 V in 2 μs). This nonlinear control is based on hysteretic control of Cout current. This system is very sensitive to effects, like aging, temperature, input and output voltage variation, etc., that modify the switching frequency. This paper proposes a frequency loop to avoid the frequency variation and to adjust the switching frequency to the nominal value by changing the hysteretic band. A 5-MHz buck converter is developed, and experimental results validate the loop design, obtaining the same fast transient response (from 1.5 to 2.5 V in 2 μs) while keeping switching frequency constant in steady state.