Voltage regulator with switching and low dropout modes

A wireless sensor module, comprising:

• a sensor;
• and
• a voltage regulator having an input terminal coupled to receive an input voltage signal and having an output terminal coupled to the sensor, the voltage regulator operable to generate an output voltage signal at the output terminal for powering the sensor and a radio, the voltage regulator comprising:
• a first transistor coupled between the input terminal and the output terminal,
• an energy storage device coupled between the first transistor and the output terminal,
• an error amplifier operable to generate an error signal having a current having a magnitude based on a difference between the output voltage signal and a reference voltage signal,
• a switching circuit including an oscillator operable in a buck mode to generate a switching signal and a latch operable responsive to the error signal in the buck mode to receive the switching signal and generate a first drive signal coupled to a first gate terminal of the first transistor for charging the energy storage device using the input voltage signal,
• a current source,
• a switch coupled between the current source and a gain terminal of the error amplifier,
• logic operable to selectively close the switch during a startup period associated with entering the buck mode to increase a gain of the error amplifier,
• a linear circuit coupled to the first transistor and operable to provide a linear signal based on the error signal to the first gate terminal of the first transistor for operating the first transistor in a low dropout mode for charging the energy storage device using the input voltage signal, and
• a controller operable to selectively enable the switching circuit in the buck mode for generating the output voltage signal and to enable the linear circuit in a low dropout mode for generating the output voltage signal responsive to an operating mode of the radio.

A voltage regulator comprising:

• a first transistor coupled between an input terminal and an output terminal;
• an energy storage element coupled between the first transistor and the output terminal;
• an error amplifier operable to generate an error signal having a current having a magnitude based on the difference between an output voltage signal at the output terminal and a reference voltage signal;
• a switching circuit coupled to the first transistor, the switching circuit operable responsive to the error signal in a buck mode to provide a first drive signal to a first gate terminal of the first transistor for charging the energy storage element;
• a current source;
• a switch coupled between the current source and a gain terminal of the error amplifier;
• a control circuitry,
• wherein, responsive to a first predetermined signal output from said control circuitry, the voltage regulator is configured to operate in the buck mode to convert an input voltage signal received at the input terminal to the output voltage signal;
• and
• logic operable to selectively close the switch during a startup period associated with entering the buck mode to increase a gain of the error amplifier,
• a linear circuit coupled to the output of the error amplifier and coupled to the first gate terminal of the first transistor, the linear circuit responsive to a second predetermined signal output from the control circuitry to provide a linear signal based on the error signal to the first gate terminal of the first transistor for operating the first transistor in a low dropout mode to generate the output voltage signal.