Design Of A Low Dropout Linear Regulator With High Power Rejection Ratio And Adjustable Output Voltage

With the continuous development of science and technology,the portable products are playing an increasingly important role in our daily lives.In this way,the designers of core power management chip face great challenges.According to the different application requirements and conversion processes,the power management chip can be divided into four major categories:AC to AC,AC to DC,AC to DC,DC to AC,and DC to DC.The Low Dropout Regulator(LDO)which is the leader of the DC-DC devices stands out from it.LDO regulators are widely used in various electronic products because of its advantages of high precision and high stability and simple peripheral circuits.However,LDO can only achieve the function of step-down due to the limitations of its own structure.At present,it is currently moving toward the trend of low power consumption,high integration,high power supply rejection ratio,rapid response,and high stability.We design a low dropout linear regulator with high power supply rejection ratio and adjustable output voltage.Power consumption can be reduced by increasing the power supply rejection ratio(PSRR)of the entire LDO.In this way,it also can improve system accuracy.And the application range of the chip can be increased by adjusting the output voltage.Specific research idea is that the key modules of the bandgap voltage reference and error amplifier are in innovative design and innovated to improve the PSRR.The cascade structure is used for bandgap reference voltage to increase the PSRR.Different current was extracted at different temperatures when using the circuit structure of the current extraction.A positive temperature coefficient current could be extracted from its output branch in the period of high temperature,on the contrary,a negative temperature coefficient current could be extracted in the period of low temperature.In this way,the voltage reference source had multiple poles in the whole operating temperature range and the goal of lower temperature drift coefficient was achieved.By the way,it provides a high precision reference voltage to the system.The error amplifier is used with the multi-level Operational Amplifier structure of two-stage output stage and a buffer stage.Two output stages ensure high gain of the Operational Amplifier.The buffer stage adopts class-AB push-pull buffer structure to ensure rapid charge and discharge of the regulating gate and achieve fast response.In order to enhance system stability,the error amplifier is added with Miller compensation circuit to the system.Two signal paths are designed for the power supply VDD.The PSRR of the operational amplifier is affected by controlling the output resistance of the path to achieve the purpose of increasing the PSRR.In order to realize the output voltage adjustable and reach the goal of expanding the output voltage range,we add MOS access switch to the appropriate output terminal of the resistor.The turn-off condition is controlled and the total output resistance value is adjusted by controlling the gate voltage of each switch tube.In this way,the goal of adjustable output voltage is achieved.The design is based on the HHGRACE BCD 0.35 μm process.We completed the circuit simulation under different models,input voltages,and process angles.The results show that when the input voltage is in the range of 2.7V to 5.5V,the output voltage is 1.225V to 5.5V-VDO.The maximum output current is 1.5A and the maximum leakage voltage is 580mV@1.5A.With a high power supply rejection ratio,the power supply rejection ratio can reach 74dB at a typical frequency of 10kHz.At the same time,the chip has the functions of enabling shutdown,over-temperature protection,under-voltage protection and output current limiting protection.