Controller and control method for DC-DC converter

A controller for a DC-DC converter including a first transistor receiving input voltage and a second transistor coupled in series to the first transistor, the controller comprising:

• a circuit controlling the first transistor and the second transistor to select either one of a first mode in which the DC-DC converter operates as a switching regulator and a second mode in which the DC-DC converter operates as a linear regulator,
• wherein output voltage and output current changing in accordance with the output voltage are generated through a node between the first transistor and the second transistor, and
• wherein the circuit includes a mode control circuit which monitors the input voltage, the output voltage, and the output current, the mode control circuit including:
• a multiplier which determines a load current in which efficiency of the switching regulator and efficiency of the linear regulator are substantially the same based on a consumption current consumed in the controller, a monitored input voltage and a monitored output voltage, and
• a comparator which compares the load current with a monitored output current, and generates a mode control signal for selecting the one of the first mode and the second mode based on a comparing result.

A method for controlling a DC-DC converter that includes a first transistor receiving input voltage, a second transistor coupled in series to the first transistor, and a controller which controls the first transistor and the second transistor to select either one of a first mode in which the DC-DC converter operates as a switching regulator and a second mode in which the DC-DC converter operates as a linear regulator, wherein output voltage and output current changing in accordance with the output voltage are generated through a node between the first transistor and the second transistor, the method comprising:

• monitoring the input voltage, the output voltage, and the output current;
• determining a load current in which efficiency of the switching regulator and efficiency of the linear regulator are substantially the same based on a consumption current to be consumed in the controller, a monitored input voltage, and a monitored output voltage;
• comparing the load current with a monitored output current;
• and
• based on a comparing result, generating a mode control signal for selecting one of the first mode and the second mode.