The Study Of Low Drop-out Regulator For Buck DC-DC Convertor

With the rapid development of mobile communication technology, low-power, high efficiency power management technology become an inevitable trend. The paper presents a new power management solution that combine a LDO linear regulator with a buck DC-DC convertor , this solution makes the use of low noise, high stability LDO output to providing high quality power for buck DC-DC convertor.With combination of the above design requirements, this paper presents a suitable structure of a LDO regulator for switching power supply. This structure uses the LDO output to drive the reference source, reduce system noise and power consumption.Through systematic analysis of LDO, the loop will be more stable after adopting appropriate compensatory measures. In accordance with program needs, this structure designs a output stage which have two kinds of switching stage. The output can supply the power for the internal circuits, and also can directly drive the external loads. In addition, the structure increase a functional circuit including the comparator and logic control modules to ensure the reference source working perfectly. This paper uses the BiCMOS manufacturing process which contains high speed bipolar devices and MOS device, this process can make the circuit better realized.Using the software of Hspice to simulation the LDO system, the result shows that the system can work perfectly, the performance of each sub-module circuit can meet the design requirements.The range of the LDO input voltage is 3~6.5V,and operating temperature range is -25~125℃. In the condition of the input voltage 2.5V and temperature 25℃, the LDO output voltage is 2.8V, the maximum output current is 180 mA, and the dropout voltage is 200mV. This thesis is a worthwhile experience about the new power management.