11.7 A Wide 0.1-to-10 Conversion-Ratio Symmetric Hybrid Buck-Boost Converter for USB PD Bidirectional Conversion
Cheng Lin, Chieb-Sheng Hung, Siyi Li, Ya-Ting Hsu, Ke‐Horng Chen, Kuo-Lin Zheng, Ying-Hsi Lin, Shian-Ru Lin, Tsung-Yen Tsai
Abstract
In recent years, USB Power Delivery (USB PD) is playing an increasingly important role in the field of consumer electronics. The USB PD 3.1 extends the delivering voltage up to 48V, which requires a buck-boost converter with extreme conversion ratio <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\text{CR}= \mathrm{V}_{\text{OUT}}/\mathrm{V}_{\text{IN}})$</tex> range from 0.1″,10, high-voltage (HW) stress switches, and fast transient response. Into the bargain, the USB Type-C interface with USB PD specification allows power delivery through a single port, which brings about the necessity for bi-directional power converter. To fulfill this task, one of the most common proposals is to implement two power converters for each direction, but this method will be costly to accomplish and will complicate the designs for controllers. Although the Three-level Buck-Boost converter (TLBB) in [1] can provide buck-boost conversion when <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{2} > 2\mathrm{V}_{1}$</tex> (top left of Figure 11.7.1), node <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{\mathrm{x}}$</tex> will be 2 times <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{1}$</tex> , which leads to inductor charging in both <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\varphi 1,\varphi 2$</tex> , and fails to transfer power from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{2}$</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{1}$</tex> . To transfer power from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{2}$</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{1}$</tex> by using the double step-down converter (DSD) [2], <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{1}$</tex> needs to be 4 times larger than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{2}$</tex> due to the limit of CR. In prior DC-DC converters, it is hard to achieve both wide-range CR and bi-directional power conversion. Thus, this paper proposes a symmetric hybrid buck-boost converter (SHBB), which contains two adjustable voltage switched-capacitor (AVSC) cells to satisfy the specifications mentioned above, as well as bi-directional power transmission. Conventional buck-boost (CBB) converter can reach full-range CR, but it encounters low CR=0.1 in the case of 48-to-5V conversion, leading to difficulty in driver and controller designs. The bottom-left of Figure 11.7.1 shows the CR range comparison chart with state-of-the-arts. The DSD converter [2] can provide extreme CR (24V to 1 V) with relatively wider duty cycles, but its maximum CR is limited to 0.25, which is not qualified for USB PD 3.1. Regarding boost conversion, the hybrid boost converter [3] and 3-switch boost converter [4] provide CR larger than 4, but they still fail to meet USB PD 3.1 requirements. The state-of-the-art buck-boost converters [1], [5] can operate in both buck and boost modes but the maximum CR is only 2. Furthermore, since the input and output voltage will vary from 5V to 48V, to tolerate high voltage stress over 96V <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(2\times \mathrm{V}_{\text{in}})$</tex> in [5], 48V <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\mathrm{V}_{\text{in}})$</tex> in CBB, and [1], the usage of 60V HV process is unavoidable, which increases fabrication cost and decreases efficiency.