Studies On System Robustness And Fast Response Of Integrated Voltage Regulators

Due to its characteristics of low-cost, high integration and high reliability, integrated voltage regulator is widely used in electronic systems, especially in portable systems. With the increase of power, speed and complexity of application systems, integrated voltage regulators need to provide more accurate, faster, more flexible and more reliable control to meet the demand for the system power. In this dissertation, integrated voltage regulator is taken as the research object. It takes a lot of efforts to focus on the design method and circuit implementation to improve system robustness and response speed when the load, voltage, temperature and working condition change. The contributions of this dissertation are listed below.1. Adaptive compensation methods. Through the theoretical analysis, a mathematical relationship of the optimal slope compensation is established to solve the sub-harmonic oscillation problem in current-mode DC-DC converter. Based on this relationship, an adaptive slope compensation circuit is proposed, which is applicable to buck, boost and buck-boost converters. In addition, based on the analysis of the principle of temperature compensation, a CMOS voltage reference with piecewise curvature compensation is proposed. The amount of compensation adapting to the changes of temperature significantly reduces the temperature coefficient of voltage reference.2. Soft-start circuit for switching regulators. An on-chip soft-start circuit based on DAC control for DC-DC switching regulator is presented. By using the techniques of DAC control and soft-start voltage sense, the rush current and overshoot of the output voltage during start-up are eliminated effectively. At the end of star-up the biased current of the soft-start circuit is cut off completely, consequently it is power-efficient. In addition, a soft-start circuit with hiccup control and adjustable start-up time both internally and externally is proposed. The combination of hiccup control and soft-start enhances system reliability. And the conversion of internal and external soft-start time is naturally, which enhances system flexibility.3. A transient response enhancing circuit is proposed. The monitor circuit generates a dynamic bias current when the output voltage jumps. This dynamic bias current is added into error amplifier and driver circuit to enhance response speed of the system. When the output is stable, this dynamic bias current disappears, which guarantees the low quiescent current design. 4. A linear regulator with 3A source and sink current capability is designed for the bus terminal. The regulator employs a NMOS pass transistor, which not only improves the system current capacity but also ensures the case of low output voltage. Using the feedback of the load current, dynamic bias and adaptive compensation are realized, and the system response and stability are optimized.5. An adaptive on-time control buck controller is presented. The techniques of input feedforward and output feedback are adopted to solve the problem of switching frequency variation in COT control. By using the charging current compensation circuit, the linearization of on-time with input voltage is realized. The time-ahead of charging circuit counteracts the impact of propagation delay on the switching frequency, which ensures the fixation of the converter's switching frequency. The auto-skip PFM mode boosts conversion efficiency during light load.6. A current-mode adaptive on-time buck controller is proposed. The current-mode control not only obtains excellent transient response speed, but overcomes the dependence of loop stability on output voltage ripple in voltage-mode. The sample-hold and time-ahead of charging circuits are adopted to ensure the fixation of the converter's switching frequency.