A LDO Design Capacitor-less With Fast Transient Response

Low Dropout Regulator(LDO)has the characteristics of low noise,low power consumption,fast transient response and low cost,occupying more than 20%of the market share of power management chips and has gradually become an indispensable part of all kinds of electronic products.Traditional LDO depend on μF-level off-chip capacitors at the output to ensure loop stable operation.However,the large area of this LDO is no longer suitable for portable electronic devices.Therefore,the development of LDOs without off-chip capacitors has become an inevitable requirement for portable electronic devices.When the LDO without external capacitor is used as the power supply of the digital-analog hybrid circuit,the pF-level load capacitance will seriously reduce the loop stability of the LDO,and the sudden change of the load will cause the output voltage of the LDO to change greatly.Therefore,how to ensure excellent transient response performance while improving stability has become the focus of the design of this article.Based on the circuit structure of the LDO without external capacitors.Firstly,it focuses on the analysis of the factors affecting the transient response performance of the LDO without external capacitors,and proposes an adaptive transient enhancement circuit,which has a simple structure and does not consume too much quiescent current during steady-state operation.Secondly,in order to improve the loop stability of the LDO,the zero-pole distribution of the LDO without off-chip capacitors is emphasized.The two-stage amplifier output by Class AB is used as the error amplifier,and the Miller compensation capacitor is used to form multi-path nested Miller compensation(Multi-path Nested Miller,MNMC),to ensure that the LDO has sufficient phase margin within the specified load range.In order to ensure the normal operation of the LDO under low power supply voltage,this paper designs a reference voltage source with a current mode structure to provide the LDO with a reference voltage lower than 1V,the reference voltage source uses high-level temperature compensation to ensure the accurate output of the reference voltage,thereby reducing the impact of temperature on the overall circuit.Finally,over-temperature protection circuit and over-current protection circuit are added to improve the reliability of the LDO circuit.The paper is based on the SMIC 180nm process to realize the circuit design and layout design of the LDO.The simulation results show that when the input voltage is 2V-3.3V,the output voltage is 1.8V,the line regulation is 2.04mV/V,and the load regulation is 0.082mV/mA.When the load current is 100mA,the actual dropout voltage is 178mV.When the load current suddenly increases from 100μA to 100mA within 1μs,undershoot voltage of 98.1mV is generated and stabilized within 1.42μs;when the load current suddenly drops from 100mA to 100μA within 1μs,undershoot voltage of 86.8mV is generated and stabilized within 1.28μs.