LDO的环路稳定性分析.doc

2010 International Conference on Electrical and Control Engineering The Analysis of LDO and the Stability of Loop Compensation Xuewen Wang , Fengge Wang , Zhongwei Li Institute of Microelectronics, School of Information and Technology Northwest University Xi’an, China Abstract: This paper discusses loop compensation methods of II. ANALYSIS OF VARIOUS LDO COMPENSATIONS LDO. We especially analyze the LDO loop op-amp module, A. LDO Open-loop Model Ddiagram PMOS adjustment module, resistor feedback module. Moreover, the zero-pole compensation, feed-forward compensation and ESR compensation are adopted simultaneously to compensate LDO. This article simulates the designed LDO system with the CSMC um CMOS technical model. The system can meet the stability requirements under the load capacitance of 0.1uF. Keywords: LDO, stability of compensation, Miller compensation, feed-forward compensation, ESR Compensation Based on the stability theory of feedback system if the closed-loop system aims to stabilize the phase of open-loop circuit system changes can not be too large, that is to say, there must be a certain degree of phase margin. Generally the phase margin is greater than 60 degrees to meet industrial applications. Therefore, to study stability problems of LDO system, firstly, we must make an open-loop AC analysis of LDO system, open the loop in the feedback way as is shown in I. INTRODUCTION Figure 1. Low Dropout Voltage Regulator (LDO), compared with the general linear regulators has the characteristics of low dropout and high conversion efficiency. It has a wide range of application prospects in the field of portable electronic products. However, if we add a common-source inverting amplification for PMOS pass element, it will have a high output impedance, which makes the output pole location change with Figure 1. Open-loop Simulation of the LDO AC Circuit the load and the circuit stability low. So we need the LDO Frequency Compensation loop to meet its requir