A Design Of Low Dropout Linear Regulator With Backup Supply Switching

The thesis focuses on the design of an LDO regulator with backup-supply switching function. The circuit can easily change its modes between LDO regulator and backup-supply and the output voltage is free of "glitch", meanwhile its merits including large output current and lower ground current. With these features it is very suitable for the charging module of the portable devices like cell phone, mp3 player, digital camera and etc.The circuit has two modes, when the input voltage is above 4.5V, it works in the LDO mode, and provides stable output voltage 3.3V. When the input voltage drops below 4.4V, it operates in backup-supply mode, and the circuit directly connects the output to the backup-supply. The whole design contains Error Amplifier, Pass Element, Bandgap Reference, Feedback Resistors, which works for LDO mode and low resistance PMOS switch, Logic Control & Supply-Switching needed by backup-supply mode, the over-current and overheat protection circuit to keep the IC works safely. The thesis discussed and introduced important sub-circuit designs in details. The design is based on the Hynix 0.5um standard CMOS process, and operation voltage range is from 4.4V to 6V. The simulation results imply that the line regulation and load regulation of the LDO is 0.8 %/V and 1 %/mA separately. Other simulation results of LDO are also given in the thesis.