A Fast Trancsient Response And Capacitor-free Low-dropout Linear Voltage Regulator

For the current power management chips, although LDO’s efficiency is not asgood as the DC/DC,few peripheral devices, small size, fast response of the input/output and small output noise characteristics make LDO become widely used in manypower managements in portable products.LDO is composed of error amplifier、pass element、bias、bandgap reference、feedback resistor network and related protection circuit。This paper analysis the basicprinciple of LDO(low-dropout linear regulator), and its parameters. Designs a fasttransient response capacitor-free LDO on the basis of above.The chopper modulation isused in bandgap to achieve the suppression of offset and noise. In the error amplifierserises a buffer on the basis of the traditional miller capacitor compensation toeliminate the right plane zero to ensure the stability of the system. Moreover,design alow output impedance buffer to drive the power mosfet, not only can drive the gatecapacitance, and push the pole of buffer so far, so as not to affect the stability. Anautomatic sense network is proposed to improve LDO’s transient response. In thispaper, parameters of LDO’modules are optimized. LDO’s layout are completed andsimulations based on Spectre are given. Related over-current and over-temperatureprotection circuit are designed to prevent the permanent damage of the chop whencircuit is abnomal working.The circuit used CSMC0.5μm process to design, simulation results show that thenormal operating voltage of LDO is3.5V to6.5V, the output is3.3V, the rang of loadcurrent range is1mA to100mA,undershoot and overshoot are135mV and60mV, lineregulation and load regulation are0.023%and0.5%, all of this achieve the expectedgoal.