This paper presents the design of a LDO-assisted DC-DC converters in Cadence Virtuoso based on a 350-nm CMOS technology. This kind of voltage regulators consists of a switching converter together with a classic or LDO (low dropout) linear voltage regulator. While the linear regulator provides the constant output voltage, the switching converter conducts nearly all the current provided in the output load, and keeping the regulator current close to zero where the higher efficiency is achieved. In addition, current article shows the modeling in Matlab/Simulink. This modeling is mandatory in order to predict and assure the stability of the circuit. In addition, it can allow improving the performance of the circuit.