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

A method comprising:

• generating a first ramp using a first current source having a current level proportional to an input voltage of a buck-boost converter;
• generating a second ramp using a second current source having a current level proportional to an output voltage of the buck-boost converter;
• generating a first threshold voltage proportional to a difference between the input voltage and the output voltage of the buck-boost converter;
• generating a second threshold voltage proportional to the input voltage of the buck-boost converter;
• comparing the first threshold voltage with a sum of the first ramp and a first predetermined offset voltage using a first comparator;
• comparing the second threshold voltage with a sum of the second ramp and a second predetermined offset voltage using a second comparator;
• terminating a gate drive signal of a low-side switch of a buck converter portion of the buck-boost converter based upon a comparing result generated by the first comparator;
• and
• terminating a gate drive signal of a high-side switch of a boost converter portion of the buck-boost converter based upon a comparing result generated by the second comparator.

A converter comprising:

• a first high-side switch and a first low-side switch connected in series between an input voltage terminal and a ground;
• a second high-side switch and a second low-side switch connected in series between an output voltage terminal and the ground;
• an inductor connected to 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 control apparatus configured to generate gate drive signals, wherein the control apparatus comprises:
• a first timer for setting a turn-off time of the first low-side switch, wherein the turn-off time of the first low-side switch is generated based on a first threshold voltage proportional to a difference between an input voltage of the converter and an output voltage of the converter, wherein the first timer comprises a first input configured to receive a first ramp and a second input configured to receive the first threshold voltage, and wherein the first ramp is generated by a first current source having a current level proportional to the input voltage of the converter;
• a second timer for setting a turn-off time of the second high-side switch, wherein the turn-off time of the second high-side switch is generated based on a second threshold voltage proportional to the input voltage of the converter, wherein the second timer comprises a first input configured to receive a second ramp and a second input configured to receive the second threshold voltage, and wherein the second ramp is generated by a second current source having a current level proportional to the output voltage of the converter;
• and
• a peak current mode control device for setting a turn-off time of the first high-side switch and a turn-off time of the second low-side switch.