Battery charging circuit with improved system stability and control method thereof

A battery charging circuit, comprising:

• a switching circuit having at least one switch and an inductor coupled to the at least one switch;
• a bias reference circuit having a first input terminal configured to receive a charging current feedback signal and a second input terminal configured to receive a charging current reference signal, wherein the bias reference circuit proportionally integrates a difference between the charging current feedback signal and the charging current reference signal and provides a bias reference signal at an output terminal when a battery voltage is higher than a first threshold and less than a second threshold, wherein the first threshold is less than the second threshold;
• a bias generator coupled to the output terminal of the bias reference circuit to receive the bias reference signal, wherein the bias generator proportionally integrates a difference between the sum of the bias reference signal and a system voltage reference signal and a system voltage feedback signal, and provides a bias signal at an output terminal;
• a comparison circuit having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal is configured to receive the sum of the bias signal and the system voltage reference signal, and the second input terminal is configured to receive the sum of the system voltage feedback signal and a ramp signal, the comparison circuit provides a comparison signal at the output terminal;
• a constant time period control circuit configured to provide a constant time period control signal;
• and
• a logic circuit configured to receive the comparison signal and the constant time period control signal, wherein the logic circuit provides a control signal at an output terminal to control the at least one switch.

A control method for controlling a battery charging circuit having at least one switch and an inductor coupled to the at least one switch, the control method comprising:

• generating a first difference signal based on the difference between a charging current feedback signal and a charging current reference signal;
• generating a bias reference signal by proportionally integrating the first difference signal when the battery voltage is higher than a first threshold and less than a second threshold, wherein the first threshold is less than the second threshold;
• generating an error signal by subtracting a system voltage feedback signal from the sum of the bias reference signal and a system voltage reference signal;
• generating a bias signal by proportionally integrating the error signal;
• comparing the sum of a system voltage feedback signal and a ramp signal with the sum of the bias signal and a system voltage reference signal and generating a comparison signal;
• generating a constant time period control signal;
• and
• generating a control signal for controlling the at least one switch based on the comparison signal and the constant time period control signal.