A Continuous-Output-Current Buck-Boost Converter Without Right-Half-Plane-Zero (RHPZ)

This paper presents a high-efficiency continuous-output-current buck-boost (COCBB) converter with a single buck-boost mode operation. The proposed COCBB comprises one flying capacitor (CF), one power inductor (L), and five power switches (S-1 to S-5). With the help of a flying capacitor, the proposed COCBB converter allows its power inductor to continuously deliver output current while achieving a wide conversion ratio range of D/(1 - D), without right-half-plane-zero (RHPZ). With the continuous output current delivery, the circuit exhibits a small output voltage ripple, good transient response and high efficiency. We employ a double clock timing (DCT) control method to obtain a smooth controller-mode transition between the DCT control and pulse-width-modulation (PWM) control for different load conditions. Fabricated in 0.18 mu m CMOS, the prototype chip regulates an output voltage of 1.6 V from a 1.4 V to 1.8 V input range and revealing an undershoot/overshoot of 90/30 mV under the load transient steps between 100 mu A and 900mA. The measured output ripple is only 10 mV with a loading current of 400 mA. Also, the converter manifests a peak efficiency and a current density of 95.5% and 0.46 A/mm(2), respectively.