Approach to the Implementation and Modeling of LDO-Assisted DC-DC Voltage Regulators Herminio Martínez-García Department of Electronics Engineering Eastern Barcelona School of Engineering (Escola d’Enginyeria de Barcelona Est, EEBE) Technical University of Catalonia (UPC). BarcelonaTech Diagonal-Besòs Campus. Eduard Maristany Ave., nº 10 – 14 E–08019 - Barcelona. SPAIN E-mail: herminio.martinez@upc.edu Abstract—This paper presents the design of an LDO-assisted DC-DC voltage regulator in Cadence Virtuoso ® based on a 350- nm CMOS technology. This kind of voltage regulator consists of a switching converter together with a classic or LDO (low drop- out) linear voltage regulator. While the linear regulator provides the constant output voltage, the switching converter conducts nearly all the current provided to the output load, and keeping the regulator current close to zero where the higher efficiency is achieved. In addition, this paper shows the modeling in Matlab/Simulink. Notice that, this modeling is mandatory in order to predict and assure the stability of the circuit. In addition, it will help to improve the transient response and performance of the circuit. Keywords— DC-DC Converters; Low Drop-Out (LDO) Voltage Regulators; Power Electronics; Modeling of Power Converters; Matlab/Simulink. I. INTRODUCTION There are substitute renewable energies that are known as cutting-edge technology. They will be fundamental subsystems in electrical energy grids in the future. This is the case, for instance, of high voltage DC (HVDC) transmission. Since they cannot be connected directly, and in order to interconnect these subsystems into the grid to enlarge the possibility of integration, power electronic converters and devices will be required. Because power regulators are quite more flexible in terms of control, have become the most concerning technology for researchers in modern power system. In fact, DC-DC power regulators are widely used in a significant variety of applications in terms of their high efficiency and low output ripple, such as portable devices, energy-harvesting applications and radio frequency (RF) power amplifiers that are in need of highly efficient and stable power supply [1]–[3]. There are two main approaches for the design of DC-DC power regulators such as using either switching regulators or linear regulators. On the one hand, DC-DC switching regulators could show residual or spurious ripples in the output voltage due to the switching process. Thus, the use of linear regulator would be necessary to eliminate these ripples and produce the surplus of the current that is not provided by the switching regulators [4]. In general, linear-assisted hybrid voltage regulators usually consist of a switched-inductor (buck or step-down) converter with a linear regulator (standard NPN Darlington pair, LDO or quasi-LDO) in order to provide the desired output current flowing through the load with regulated constant output voltage. Previous researches have been done to minimize the existing impediments such as low efficiency and high power dissipation [5],[6]. Other works have proposed topologies in order to optimize the performance of buck converter or improve the control techniques [7]–[9]. Moreover, other researches have optimized the design using push-pull linear regulator [10]. In this article, a proposal of linear-assisted DC-DC regulator and its modeling is presented to inquire the control loop stability. In fact, in order to carry out the stability study, a model of the whole system is necessary. In particular, on the one hand, an LDO regulator is used that has benefits of maximizing the use of available input voltage and can yet regulate the input voltage while both input/output values are close to each other, minimizing internal power loss. In this structure, the conventional linear regulator is replaced by an LDO in order to obtain the better performance (lower output ripple and better efficiency). In addition, an approach to the modeling of the circuit is presented in order to analyze the stability based on critical parameters’ variation. II. STRUCTURE OF THE PROPOSED LDO-ASSISTED DC-DC REGULATOR In the proposed circuit shown in Fig. 1, the switching converter is connected in parallel with an LDO regulator, providing the desired output current and voltage to the load. As it is well known, the LDO regulator, thanks to the feedback loop of the operational amplifier and resistors R1 and R2, continuously compares the reference Vref1 and the feedback sample obtained from the output voltage in order to provide a constant output voltage. Therefore, this output voltage, Vout, is given by: 978-1-5386-5108-7/17/$31.00 ©2017 IEEE