Dual Input LDO Regulator With Controlled Transition Between Power Supplies

A Power Management IC (PMIC) comprising:

• a first voltage terminal for receiving an unregulated supply voltage having a first voltage level;
• a regulated power source coupled to the first voltage input terminal for generating a regulated supply voltage on a second voltage terminal, the regulated supply voltage having a second voltage level that is lower than the first voltage level;
• a dual input low drop out (LDO) regulator for generating a regulated output voltage on an output terminal, the LDO regulator comprising:
• a first regulator circuit including a first output device coupled between the first voltage terminal and the output voltage terminal, and a first control circuit for controlling the first output device;
• a second regulator circuit including a second output device coupled between the second voltage terminal and the output voltage terminal, and a second control circuit for controlling the second output device;
• and
• means for controlling the first and second regulator circuits such that:
• during a first operating phase, the first regulator circuit passes the unregulated supply voltage from the first voltage input terminal to the output voltage terminal,
• during a second operating phase, the second regulator circuit passes the regulated supply voltage from the second voltage input terminal to the output voltage terminal, and
• during each change-over period between the first and second phases, both the unregulated supply voltage and the regulated supply voltage are simultaneously passed to the output voltage terminal for a predetermined delay period.