Handheld Devices Using Ldos Ic Design

In recent years,low dropout linear regulator has received more and more attentions in numerous power management chips because of its small area,low noise,low supply current,few off-chip components. It has widely used in many kinds of portable applications.However, the market of power management chips is mainly shared by foreign companies,which make research of LD0 chip more meaningful nowadays.This paper introduced all kinds of regulator in the mainstream market nowadays and gave a close glance to their working principles plus their advantages and disadvantages than focus on major function blocks of LD0 and design rules,ways of optimization for per blocks. With principle given above,I design & simulate the device L2985 from National Semiconductor company.During the design,casecade current mirror was applied to enhance high gain under low Vcc condition.And to get better thermal performance of voltage reference,I design with first order bandgap voltage reference and PTAT current.To simulate the design,I used Cadence Spectre and PSRR is larger than 60dB, current consumption under full loading is lower than 500uA which meet the spec.The last chapter of the paper discussed about the way to further enhance the performance of LDO device,pin-point to every function block,second order bandgap structure to improve thermal performance and improved buffer structure to higher current efficiency.And the direction for development of LDO devices has been discussed as well.