Seamless dcm-pfm transition for single pulse operation in dc-dc converters

A control circuit operable to switch a transistor on and off at a switching frequency to convert an input voltage at an input node to an output voltage at an output node coupled to a load, the control circuit comprising:

• an error amplifier circuit operable to generate a control current and having a first output operable to output a first current and a second output operable to output a current, the first output current and the second output current are equivalent to the control current;
• a peak current comparator circuit having a first input coupled to the second output of the error amplifier circuit, a second input and an output, the second input is coupled to the input node through an inductor;
• an off-time timer circuit having an input coupled to the first output of the error amplifier circuit and an output, the off-time timer circuit operable to set the switching frequency based on the control current;
• and
• a control circuit having a first input coupled to the output of the peak current comparator circuit, a second input coupled to the output of the off-time timer circuit and an output coupled to a control terminal of the transistor.

A method of operating a converter operable to convert an input voltage at an input node to an output voltage at an output node coupled to a load, the method comprising the steps of:

• switching a transistor on and off during a heavy load period at a fixed switching frequency to provide pulses of current to the load and varying a maximum current per pulse of current;
• switching the transistor on and off during a light load period at a fixed maximum current per pulse of current and varying the switching frequency;
• and
• switching the transistor on and off during a period between the heavy load period and the light load period by varying the switching frequency and the maximum current per pulse of current.