Novel dynamic ramp circuit with input feedforward for voltage-mode DC-DC buck converter

A novel dynamic ramp circuit with input feedforward technique for voltage-mode DC-DC buck converter is presented. By converting a charging current proportional to input voltage skillfully, the ramp amplitude varies with input voltage and the gain of modulator maintains substantially constant. Also the minimum value of the saw-tooth wave could be set freely by the introduction of clamp circuit. The proposed circuit can improve the stability and line transient response under various input voltages. A monolithic DC-DC buck converter with 2.25MHz frequency using the proposed circuit has been fabricated with a 0.5μm CMOS process for validation. With 2V line transient response, the undershoot and overshoot output voltages are about 35mV and 30mV, respectively.