A 12V-Input 1V-1.8V-Output 94.7%-Peak-Efficiency 685A/cm³-Current-Density Hybrid DC-DC Converter with a Charge Converging Phase

Abstract

Large voltage-conversion-ratio (VCR) DC-DC converters (e.g. 12V to 1-to-1.8V) with high efficiency and high current density are essential for industrial and automotive applications. Conventional buck converters have to use high-voltage transistors that incur large power loss and bulky inductors that occupy significant board area, leading to compromised efficiency and current density. Recent advancements in hybrid converters [1] –[6] provide promising solutions for such applications. These converters introduce flying capacitors to lower the voltage stress of the power transistors or to reduce the inductor current $\left(\mathrm{L}_{\mathrm{L}}\right)$. For instance, double step-down (DSD) related converters [1], [2] and a switched-capacitor buck converter [3] are proposed to lower the voltage stress of the power transistors to up to $\mathrm{V}_{\mathbb{I}} / 4$, allowing the use of low-voltage transistors for improved efficiency. However, the inductors still have to handle the entire output current $\left(\mathrm{I}_{0}\right)$ as that in a conventional buck converter, requiring bulky inductors with low DCR and thereby limiting current density. Dual-path hybrid converters are proposed in [4] –[6] to reduce I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</inf> by leveraging the flying capacitors to provide additional current paths. However, the reduction in I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</inf> is relatively modest, only 20% in [4], [5] for a 12V-to-1.2V conversion scenario. Although [6] achieves a significant reduction of 40%, it requires a complex switched-capacitor network with 12 switches. In this paper, we propose a dual-path hybrid buck converter featuring a charge converging phase (CCP-HB) that consistently reduces $\mathrm{I}_{\mathrm{L}}$ to less than $0.5 \mathrm{I}_{0}$.

Topics & Concepts