Automated Synthesis Design Flow of Power Converter Circuits Aimed at SOC Applications Hsin-Yu Luo, Hsiu-Wen Li*, Long-Ching Yeh and Chien-Nan Jimmy Liu. Department of Electrical Engineering, National Central University, Taiwan, ROC {985201030, 945401024}@cc.ncu.edu.tw and {lcyeh916, jimmy}@ee.ncu.edu.tw *the corresponding author Abstract—In this paper, we propose a power converter synthesis design flow aimed at SOC applications. A buck DC-DC converter and a low dropout (LDO) linear regulator, both with controllers are studied. We apply both the knowledge-based and the simulation-based methods in the proposed flow and they lead to an accurate result when it is compared with the design specification. Demonstration cases validate our work. I- INTRODUCTION Recent development of SOC integrates the digital and the analog/RF circuits, as well as the power processing circuit on a chip. The computer aid design tools for SOC have provided a complete and successfully support for the digital circuit design already. However, designers still need to adjust the analog and the RF circuit designs manually. Moreover, on chip power processing circuits to power different blocks of a SOC chip become a trend and their designs become very complicated [1]. Therefore, since the electronic industry is concerned about time to market, this may require the EDA tool to assist those designs. TABLE I shows the comparisons of linear regulators and switching converters [2]. The buck converter can be applied to portable electronic products with high efficiency, like LCD-TVs, internet communication chips and cell phones. However, the inductor in the buck converter occupies a large area and it defeats the purpose of a SOC design. To reduce the size of switching converters, one can integrate the switches and the controller circuit in the SOC but leave the inductor and capacitors for off-chip connections. In the case of LDO, its efficiency is dominated by the input voltage and the output voltage difference, and thus the low drop out voltage is necessary. To combine the advantages of both the switching converter and the LDO's, one can connect a switching converter followed by a LDO to improve the fast transient response, such as a CPU load under a demand of intensive calculation [3]. An TABLE I. COMPARISONS OF DC-DC CONVERTERS Parameters Linear Regulator Switching Converter Efficiency Low High Power Rating Medium High Size(PCB Real Estate) Compact Large Cost and Complexity Low High Noise Low High LDO alone can also be used for sensitive circuits, like audio amplifiers, analog and RF circuits. Because the buck converter and the LDO are often used as the power conversion units in SOC design, we select these two circuits as the test vehicle of automatic synthesis flows in this paper. II- BUCK CONVERTER SYNTHESIS FLOW Fig. 1 shows the buck converter circuit and Fig. 2 shows the buck converter synthesis flow. We use the closed form equations to calculate the design parameters. We also use the closed form equations to do the small signal analysis where the equations are the linearized equations unique to the switching power converter topology. Finally, we add HSpice to simulate the entire circuit to verify the design. As shown in Fig. 2, it starts with the input of specs listed as follows: the supply voltage (V i ), the output voltage (V o ), the max load current (I o,max ), the ripple current (I L,pp ), the ripple voltage (V o,pp ), the switching frequency (f s ) and the target efficiency. Next, steady state analysis is carried out to find the corresponding parameters of the buck converter in steady state operation, such as: the duty cycle (D), the inductance (L), the capacitance (C), and the width of the MOSs (W p & W n ) as switches. The small signal analysis is then carried out. The control circuit with a PID controller is also synthesized at this time and its small signal model is derived, the net-list is then generated before the final simulation of the entire circuit with HSpice. Among these parameters, the current ripple and voltage ripple represent slight variations of inductor current and output capacitor voltage state variables during switching respectively [4], their functions are given by equations (1) and (2). Figure 1. Architecture of buck converter