Many factors are actively driving interest towards the optimization of power consumption, such as the reduction of the thermal dissipation and the extension of the battery duration in portable devices. Interest in this matter has grown exponentially also due to the widespread adoption of portable devices in every-day life (smartphones, notebooks, e-readers and so on), which is driving the energy consumption to an unprecedented amount. Virtually every portable device contains several, if not many, DC-DC converters to convert the input DC voltage, which might be provided by a battery or by a rectifier if the source is AC, into the different DC levels required by the multiple components of the device, such as CPUs or displays. Nowadays, the area footprint of DC-DC converters is shrinking rapidly, thanks to the possibility to integrate the power transistors on chip, thus making DC-DC converters growingly attractive. To achieve regulation under varying operating conditions, a feedback loop is required and the output voltage of the DC-DC converter must be regulated to a desired reference value. Therefore, a controller for the DC-DC converter must be properly designed. The controller architecture has a direct influence on the dynamic performance during transients, and a proper design should guarantee a tight regulation of the output voltage even during transients.