Mode transitioning in a DC/DC converter using a constant duty cycle difference

A DC/DC converter, comprising:

• a buck section, the buck section configured to receive an input voltage;
• an inductor coupled to the buck section;
• a boost section coupled to the inductor;
• and
• a controller coupled to the buck and boost sections, the controller configured to monitor the input voltage for a change in the input voltage, and in response to the change in the input voltage, to control a buck duty cycle of the buck section and a boost duty cycle of the boost section during a buck/boost mode of operation such that a difference between the buck duty cycle and the boost duty cycle is substantially constant over substantially an entire range of values of the input voltage corresponding to the buck/boost mode of operation.

A DC/DC converter, comprising:

• a buck section, the buck section configured to receive an input voltage;
• an inductor coupled to the buck section;
• a boost section coupled to the inductor;
• and
• a controller coupled to the buck and boost sections, the controller configured to drive the buck section and the boost section during a buck/boost mode of operation such that a difference between a buck duty cycle and a boost duty cycle is substantially constant over a range of values of the input voltage, wherein the controller also is configured to drive the buck section and the boost section such that the buck duty cycle and the boost duty cycle are not substantially constant over the range of values of the input voltage, and the buck duty cycle and the boost duty cycle are functions of the input voltage over the range of values, and wherein
• the controller comprises
• a driving signal generator coupled to the buck and boost sections, the driving signal generator operable to generate a buck driving signal in response to a buck duty cycle signal and a boost driving signal in response to a boost duty cycle signal,
• a duty cycle generator coupled to the driving signal generator, the duty cycle generator operable to generate the buck duty cycle signal and the boost duty cycle signal in response to a mode signal and a comp signal, and
• a state machine coupled to the duty cycle generator, the state machine operable to generate the mode signal in response to the input voltage and an output voltage.

A DC/DC converter circuit for converting an input voltage applied at an input node to an output voltage at an output node, the DC/DC converter comprising:

• a buck section coupled to the input node;
• an inductor having a first end and a second end, the first end of the inductor coupled to the buck section;
• a boost section coupled to a second end of the inductor;
• and
• a controller coupled to the buck section and the boost section, the controller configured to monitor the input voltage for a change in the input voltage, and in response to the change in the input voltage, to control a buck duty cycle of the buck section and a boost duty cycle of the boost section during a buck/boost mode of operation such that a difference between the buck duty cycle and the boost duty cycle is substantially constant over substantially an entire range of values for the input voltage that corresponds to a buck/boost mode of operation of the DC/DC converter.

A method of mode transitioning, comprising the steps of:

• driving a buck section of a DC/DC converter with a buck signal that has a buck duty cycle while the DC/DC converter is in a buck/boost mode of operation, wherein the buck duty cycle comprises a first linear function of an input voltage over substantially an entire range of values of the input voltage that corresponds to the buck/boost mode of operation;
• concurrently with driving the buck section, driving a boost section of the DC/DC converter with a boost signal that has a boost duty cycle while the DC/DC converter is in the buck/boost mode of operation, a difference existing between the buck duty cycle and the boost duty cycle, wherein the boost duty cycle comprises a second linear function of the input voltage over substantially the entire range of values of the input voltage that corresponds to the buck/boost mode of operation;
• monitoring an input voltage that is coupled to the buck section for a change in the input voltage;
• and
• in response to a change in the input voltage, changing the buck duty cycle and the boost duty cycle.