A Three-Fine-Level Buck–Boost Hybrid Converter Achieving Half-VIN-Stress on All Switches and Fast Transient Response

This article presents a non-inverting three-fine-level buck-boost (3FLBB) hybrid converter suitable for lithium-ion (Li-ion) batteries. With seven power switches and two flying capacitors, the proposed 3FLBB converter produces the voltage of switching node between $V_{\mathrm {IN}}$ /2, $V_{\mathrm {IN}}$ , and $3{V_{\mathrm {IN}}}$ /2, which supports buck, boost, and buck-boost modes, and with smooth mode changes. Here, one of the two flying capacitors is used to drive the inductor (L), while another one is used to ensure that $V_{\mathrm {DS}}$ of each power switch is within 1/ $2{V_{\mathrm {IN}}}$ in all phases. Hence, the voltage stress of all the power switches is reduced to half- $V_{\mathrm {IN}}$ , and the normalized equivalent resistance and switching losses are greatly reduced by using two 1.8-V switches instead of two 5-V switches. Since the three modes all have buck-like operation, the average inductor current is reduced to always equal to the output current. Meanwhile, they all have continuous output current, similar complex pole pairs, and no right half-plane (RHP) zero, which enables fast load transient response. This design is implemented by only 1.8-V devices of a standard 0.18- $\mu $ m CMOS process, covering an input voltage range from 2.8 to 4.2 V. A 98.2% peak efficiency is measured at 2-MHz switching frequency with 2.2- $\mu $ H L, two 10- $\mu $ F flying capacitors, and one 10- $\mu $ F output capacitor. It can deliver an output current of 50–1000 mA at a 3.3-V regulated output voltage. Moreover, the measured results show that this design achieves a significant improvement on undershoot and overshoot voltage than the previous works.