Research And Design Of High Current Low-dropout Regulator

With the abundance of the functions of portable electronic devices,the requirements for power supplies of chips are getting higher and higher.As a kind of power management chip,LDO has been widely used due to its small ripple,low noise,small size and no EMI.In terms of process,the bipolar process has better drive capability than the MOS process.Therefore,many LDOs are implemented with bipolar process,especially for high load current.In this thesis,a high current LDO is designed in 2μm 40V bipolar process by using software tools such as Cadence and Hspice.The main research contents are as follows.1.A bandgap reference circuit with second-order temperature compensation is designed for the defect that the traditional bandgap reference has only first-order compensation.Based on the traditional bandgap reference circuit,the circuit compensates the reference voltage at-13°C and 52°C respectively,so that the reference voltage is less affected by the temperature change.The temperature drift in the range of-55~125°C is 1.9ppm/°C,which meets the design requirements of high precision LDO for reference voltage.2.Using miller compensation and ESR compensation to stabilize the loop.The paper analyzes the system stability conditions and studies the frequency compensation methods.By externally connecting a 22μF tantalum capacitor,the system output pole is set as the main pole.The miller compensation is used inside the error amplifier and a left half plane pole is introduced,and the ESR compensation is made by the external capacitor,so that the loop works reliably over the entire load range.It is verified by simulation that the loop phase margin is 51.69°when the output current is 1.5A,which meets the system stability requirements.3.A pre-regulator circuit is designed.The circuit has a simple structure and is pre-regulated by reverse breakdown of a zener diode.Through simulation verification,the pre-regulated voltage variation is only 580.4mV in the range of input voltage 6~26V,which meets the design requirements.4.Over-temperature protection,over-current protection and over-voltage protection circuits are designed to protect the chip from damage under abnormal operating conditions.Among them,in order to prevent the circuit from repeatedly changing the operating state at the threshold temperature,the over-temperature protection circuit achieves a hysteresis effect by sampling the current of the current amplifier.Through simulation,in the typical case,when the input voltage is 6V,the over-temperature protection forward threshold temperature is 140.6°C,the reverse threshold temperature is 129.4°C;the over-current protection threshold current is 1.924A;the over-voltage protection threshold voltage is34.7V and all of them meet the design requirements.5.The layout is designed.After simulation,this thesis studies the layout design thchnology.The layout is completed and passed DRC and LVS verification.The final layout area is2490×1505μm~2,which meets the package design requirements.