Design And Research Of A Low-Dropout Regulator With Low Noise,Fast Transient Response And High Stability

Modern electronic equipment is inseparable from power circuits,and the performance of power circuits often determines the performance of electronic products.As the main power management chip,low-dropout linear regulators are widely used in low-noise applications such as measuring instruments and communication equipment due to their small size,low noise,and ripple suppression.In this thesis,a low noise,fast transient response and high stability LDO is designed.The traditional LDO mainly obtains the phase boost through the fixed zero-point frequency compensation method of the equivalent series resistance of the output capacitor,thereby improving the loop stability of the system.In most LDO designs,a major challenge in stability is that the LDO needs to provide a wide range of output current,but when the load current changes from light to heavy load,the output pole position will move to high frequency,and the system stability will be deteriorated.There are two frequency compensation methods for LDO in this thesis.One is to add a buffer stage between the output end of the error amplifier and the driver stage,and convert the low frequency pole formed by the high resistance output end of the error amplifier and the large capacitance of the power stage into two high frequency poles;the other is to use the frequency compensation method of dynamic bias inside the power stage,and the generated pole can track the change of the output pole of the LDO,so as to realize the pole-to-pole tracking frequency compensation,so that the LDO can remain stable under heavy load conditions.A driver stage circuit is added between the buffer stage and the power stage,and the Darlington tube inside has a strong current amplification capability,which can quickly change the base current of the pass element and improve the transient response characteristics.Auxiliary protection circuits such as over-temperature protection circuit,current-limiting protection circuit,and over-saturation protection circuit are also added in this design.The over-temperature protection circuit can realize 30°C hysteresis temperature protection,and the current-limiting protection circuit can adjust the current-limiting value through an external resistor,the oversaturation protection circuit can avoid the pass element from entering the saturation region and prevent the failure of the LDO adjustment function.This thesis is based on 0.6μm 12 V dual polysilicon self-aligned bipolar process,and uses Cadence software for system-level simulation and layout design.The simulation results show that when the load current is 400 m A,the dropout voltage of this design is only 200 m V,and it has good stability in the load range of 10μA-3 A;when the load current jumps between 5 m A and 3 A,the overshoot voltage is 19 m V,the undershoot voltage is 48 m V,and the recovery time is less than 0.5μs.The LDO circuit can achieve a stable output of 2.5 V under a wide power supply voltage range of 3～12 V,and the maximum output current can reach 3 A.At a load current of 50 m A,the total integrated noise at the output from 10 Hz to 100 k Hz is 32μV_RMS.