Transient Response Improvement of DC-DC Converter by Current Mode Variable on Time Control

Constant on Time (COT) control limits equivalent duty cycle due to the minimum off time and fixed on time. Thus the transient response and voltage scaling speed can be improved by adaptively changing on time. With Current Mode Variable on Time (CM-VOT) control, the on time is adaptively controlled according to output current of error amplifier. The proposed DC-DC converter is designed with 12V input and 1.2V output voltage. The recovery time is improved from 6μs to 3μs and undershoot voltage is reduced from 40mV to 26mV. Owing to Predictive Error Amplifier (PEA) and Floating Ground Compensation (FGC), the overshoot voltage is then reduced from 50mV to 20mV and the reference tracking time is reduced from 13μs to 9μs.