8.7 A 92.7% Peak Efficiency 12V-to-60V Input to 1.2V Output Hybrid DC-DC Converter Based on a Series-Parallel-Connected Switched Capacitor

• Published in: 2024 IEEE International Solid-State Circuits Conference (ISSCC) Vol. 67; pp. 156 - 158
• Main Authors: Choi, Hyeon-Ji, Lee, Chan-Ho, Jeon, Young-Jun, Park, Hyeonho, Kim, Jeong-Hun, Woo, Young-Jin, Hong, Ju-Pyo, Jin, Haifeng, Hong, Sung-Wan
• Format: Conference Proceeding
• Language: English
• Published: IEEE 18.02.2024
• Subjects: Automotive applications; Batteries; Buck converters; Capacitors; Topology; Transient response; Voltage
• ISSN: 2376-8606
• DOI: 10.1109/ISSCC49657.2024.10454344

The battery voltage (\mathrm{V}_{\mathrm{bat}}) is becoming higher in automotive applications for a higher efficiency power system. Accordingly, an ultra-low voltage-conversion-ratio (VCR) buck converter is in great demand. Previous ultra-low VCR buck converters use flying capacitors ( \mathrm{C}_{\mathrm{F}}\mathrm{s}) and power switches between the battery and the inductor, as shown in Fig. 8.7.1 (top-right) [1-6]. In these topologies, \mathrm{C}_{\mathrm{F}}\mathrm{s} reduce the voltage stress applied to switches by dividing the \mathrm{V}_{\mathrm{bat}}, which has four major weak points. First, because of the high \mathrm{V}_{\mathrm{bat}}, \mathrm{C}_{F}\mathrm{s} and switches are used as high-voltage (HV) capacitors and LDMOSs, respectively, which are bulky and have larger parasitic components resulting in huge power loss compared to a low-voltage (LV) capacitor and CMOS. If compound semiconductors, such as GaN and SiC, are used, the power loss caused by switches can be reduced [1, 6], however, they are less cost effective than silicon devices. Second, previous converters have a problem of on-duty (D) range. Considering several types of battery and their safety margins in the vehicle, the converter is required to properly operate with a \mathrm{V}_{\mathrm{bat}} range from 12V up to 60V. Previous converters can have the D either smaller than 0.1 or larger than 0.9 when they operate at this \mathrm{V}_{\mathrm{bat}} range and an output voltage ( \mathrm{V}_{\mathrm{o}}) of 1.2V, as shown in Fig. 8.7.1 (top-left), which makes the converter vulnerable to noise. Third, previous converters have another challenge for the line transient. In the automotive application, \mathrm{V}_{bat} can abruptly vary because of external conditions, as shown in Fig. 8.7.1 (bottom-left). Since the voltage across each \mathrm{C}_{\mathrm{F}}( \mathrm{V}_{\mathrm{CF}}) is proportional to \mathrm{V}_{\mathrm{bat}}, an abrupt variation of \mathrm{V}_{\mathrm{bat}} results in an abrupt change in \mathrm{V}_{\mathrm{CF}}. This induces a huge inrush current through the \mathrm{C}_{\mathrm{F}} or unbalanced inductor currents causing fatal damage to the power switches. Lastly, previous converters suffer from a slow load transient response because the load current (\mathrm{I}_{\mathrm{o}}) is only provided by the inductor.