A High-Efficiency High-Voltage-Tolerant Buck Converter With Inductor Current Emulator for Battery-Powered IoT Devices
Yunho Lee, Woojoong Jung, Sung-Min Yoo, Tae‐Hwang Kong, Jun‐Hyeok Yang, Michael Choi, Jongshin Shin, Hyung‐Min Lee
Abstract
This article proposes a high-voltage-tolerant stacked buck converter compatible with a Li-ion battery. The proposed converter utilizes a stacked power stage with only low-voltage transistors (1.5 V) to safely convert 2.8–4.2 V battery voltage to 1 V output. The converter adopts pulse frequency modulation control in the discontinuous conduction mode to reduce power losses at light load. To maximize power efficiency for a wide range of operating conditions, the converter utilizes an inductor current emulator (ICE), which adaptively controls the peak inductor current against input voltage and load variations. The proposed converter chip was fabricated in 28-nm fully depleted silicon on insulator (FDSOI) and achieved a peak efficiency of 70% at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IN</sub> = 3.6 V (nominal Li-ion voltage), <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OUT</sub> = 1 V, and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LOAD</sub> = 1 μA. By optimizing the peak inductor current depending on <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IN</sub> with ICE, the efficiency can be further improved up to 4.1% when <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OUT</sub> = 1 V and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LOAD</sub> = 10 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> A, while ensuring small efficiency variation of 5.6% over the battery voltage range. The converter efficiently regulates 1 V output from 2.8–4.2 V input at 500 nA-1 mA load with stacked 1.5 V transistors, suitable for battery-powered IoT devices.