Analysis And Design Of Current Source In BUCK DC-DC Converter

As the core technology of high-tech and information industry, microelectronics technology has become the basis of the new economic era. While Microelectronics technology brings people many conveniences, modern complicated electronic products pose new challenges to power supplies. As a solution, power management chips emerge and have become one of the most important products in the integrated circuits industry. Power management chips provide high performance power supply, widely used in PDA, mobile phones, GPS and other portable devices. As an important component of the power management chip, current source can be easily affected by power supply and temperature in working condition. So, the research object of this paper is to improve the line regulation and temperature coefficient of the integrated current source.The purpose of this paper is to design current source circuits for a BUCK DC-DC power management chip. To adapt different application circuits, a bias current source and a reference current source are designed respectively. Based on a conventional widlar current source, this paper analyzes the relationship between output current and temperature or power supply voltage. A bias current source is obtained in adjusting the temperature coefficient through the corporate function of MOS transistor and resistance. During the design of current reference, some improvements are proposed to compensate the shortcomings of widlar current source. Firstly, the paper deduces the relationship between feedback loop gain and power supply rejection in small signal theory. Through inserting an operational amplifier into the loop, the output current with lower line regulation is achieved. Secondly, the paper considers the temperature coefficient of the reference current. Through changing the circuit structure to get additional parameters related to temperature. Many parameters related to temperature act jointly to achieve second-order temperature compensation. So, the output current with lower temperature coefficient is obtained. This paper not only explores the theory of circuit design, but also considers the impaction of process corners in the simulation. This can make the simulation results much closer to reality. The process used here is the UMC 0.6um BICMOS process. Simulated by the HSPCIE software, the simulation results meet the requirements.