A Three-Fine-Level Buck–Boost Hybrid Converter Achieving Half- ${V}_{\mathrm{IN}}$ -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.