Constant on-time regulator with increased maximum duty cycle

A method in buck switching regulator receiving an input voltage and controlling a high-side switch and a low-side switch using a feedback control loop to drive a switch output node for generating a switching output voltage, the switch output node being coupled to an LC filter circuit to generate a regulated output voltage having a substantially constant magnitude on an output node, the regulated output voltage being fed back to the buck switching regulator to a voltage divider for generating a feedback voltage on a feedback voltage node, the method comprising:

• providing a first on-time duration for the high-side switch being at least a minimum on-time and being expanded to a maximum on-time when the feedback voltage remains less than a reference voltage;
• providing a first maximum on-time or a second, extended maximum on-time greater than the first maximum on-time as the maximum on-time;
• applying the first maximum on-time when a minimum off-time was not used for the high-side switch during the previous switching cycle;
• applying the second, extended maximum on-time when a minimum off-time was used for the high-side switch during the previous switching cycle;
• and
• generating a first signal for turning off the high-side switch under a minimum on-time and variable off-time feedback control loop, the first signal turning off the high-side switch at the expiration of the first on-time duration or at the expiration of the first or second maximum on-times.