Switching scheme for step up-step down converters using fixed frequency current-mode control

A method of controlling a switching regulator that produces a regulated output signal at an output node in response to an input signal at an input node, the regulator having an inductive device, and a plurality of switching devices for providing connection of the inductive device to the input and output nodes and a ground node, the switching circuits including a first switching circuit provided for coupling the input node to a first node of the inductive device, a second switching circuit provided for coupling the first node of the inductive device to the ground node, a third switching circuit provided for coupling a second node of the inductive device to the ground node, and a fourth switching circuit provided for coupling the second node of the inductive device to the output node, the method comprising:

• driving the switching devices so as to enable the regulator to operate in a boost mode to increase the input signal, in a buck mode to decrease the input signal, and in a buck-boost mode when a difference between the input signal and the output signal is within a predetermined range, and
• preventing a transition between the buck mode and the buck-boost mode, or between the boost mode and the buck-boost mode until a predetermined condition is met,
• wherein a transition from the buck-boost mode to the buck mode is prevented until an on-time of the second switching circuit exceeds a preset maximum value.

A method of controlling a switching regulator that produces a regulated output signal at an output node in response to an input signal at an input node, the regulator having an inductive device, and a plurality of switching devices for providing connection of the inductive device to the input and output nodes and a ground node, the switching circuits including a first switching circuit provided for coupling the input node to a first node of the inductive device, a second switching circuit provided for coupling the first node of the inductive device to the ground node, a third switching circuit provided for coupling a second node of the inductive device to the ground node, and a fourth switching circuit provided for coupling the second node of the inductive device to the output node, the method comprising:

• driving the switching devices so as to enable the regulator to operate in a boost mode to increase the input signal, in a buck mode to decrease the input signal, and in a buck-boost mode when a difference between the input signal and the output signal is within a predetermined range, and
• preventing a transition between the buck mode and the buck-boost mode, or between the boost mode and the buck-boost mode until a predetermined condition is met,
• wherein a transition from the buck-boost mode to the boost mode is prevented until an on-time of the third switching circuit exceeds a preset maximum value.

A power supply system for producing a regulated output signal at an output node in response to an input signal at an input node, comprises:

• an inductive device,
• a plurality of switching circuits for providing connection of the inductive device to the input and output nodes and a ground node, the switching circuits including a first switching circuit provided for coupling the input node to a first node of the inductive device, a second switching circuit provided for coupling the first node of the inductive device to the ground node, a third switching circuit provided for coupling a second node of the inductive device to the ground node, and a fourth switching circuit provided for coupling the second node of the inductive device to the output node, and
• a switch control circuit for driving the switching circuits so as to enable the power supply system to operate in a boost mode to increase the input signal, in a buck mode to decrease the input signal, and in a buck-boost mode when a difference between the input signal and the output signal is within a predetermined range, the switch control circuit including buck-boost latch circuitry for latching a transition between the buck mode and the buck-boost mode, or between the boost mode and the buck-boost mode based on a predetermined condition, wherein
• the buck-boost latch circuitry is configured to prevent a transition from the buck or boost mode to the buck-boost mode until an on-time of at least one of the switching circuits reaches a preset minimum value, and to prevent a transition from the buck-boost mode to the boost mode until an on-time of the third switching circuit exceeds the preset maximum value.