A non-overshoot soft-start circuit for LDO was designed.The core of the circuit is to eliminate the inrush current by using the soft start strategy of linear boost.The circuit structure is simple and easy to implement.In order to solve the overshoot phenomenon,a fast comparator was designed by using the transistor and positive feedback circuit,so that the output voltage of the soft start circuit can smoothly transited to a stable working state.In order to reduce the layout area,a ramp generation circuit and an input imbalance comparator circuit were designed using a small number of MOS transistors.The soft-start circuit was integrated into a low dropout linear regulator,which was implemented in SMIC 0.18 μm BCD process,and the power supply voltage was 4.5 V.The simulation results show that the surge current is effectively eliminated by the soft-start circuit,the steady rise of the output voltage without overshoot and smooth transition to the stable working state without overshoot are realized.The circuit structure is simple,and the layout area is 98 μm×60 μm,which is convenient for the on-chip integration.The circuit can also be applied to general DC-DC regulators.
low dropout linear regulatorfast comparatorsoft startsurge currentovershoot phenomena
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