Advanced constant off-time control for four-switch buck-boost converter

An apparatus comprising:

• a buck-boost converter comprising a first high-side switch and a first low-side switch connected in series between two input terminals of the buck-boost converter, a second high-side switch and a second low-side switch connected in series between two output terminals of the buck-boost converter, and an inductor connected between a common node of the first high-side switch and the first low-side switch, and a common node of the second high-side switch and the second low-side switch;
• and
• a controller comprising a first timer and a second timer, wherein the first timer is configured to determine a turn-off time of the first high-side switch, and wherein the first high-side switch remains off during the turn-off time of the first high-side switch, and the second timer is configured to determine a turn-off time of the second low-side switch, and wherein the second low-side switch remains off during the turn-off time of the second low-side switch, and wherein the second timer determines the turn-off time of the second low-side switch based on a comparison between a first signal and a second signal, and wherein the first signal is proportional to an input voltage of the buck-boost converter, and the second signal is generated based on a signal proportional to an output voltage of the buck-boost converter.