UC San Diego

As the development of technology, devices, particularly semiconductor, have scaled down dramatically enabling the high performance of computing systems. However, when examine the entire electronics system, the total dimension is not equally scaled. It is found that magnetic devices are the bottleneck for the dimensional scaling. In this dissertation, several commonly employed methods for reducing the usage of inductors are discussed and compared, including high switching frequency converter, switched-capacitor converter, hybrid converter and resonant converter. Each of these converters has been proved that partially meet the requirement of miniaturized system with fine regulation and high energy efficiency. In the following chapters, three approaches that address the problem from circuit operation, circuit technique and circuit topology are proposed.

The first one is multi-phase operation of a hybrid converter, as discussed in Chapter.3. With multi-phase operation instead of dual-phase which is more commonly used, the effective frequency over the output inductors is 3 times higher leading to smaller inductors. While retaining the benefits of using a Dickson-Star hybrid converter, such as high conversion ratio, soft-charging of flying capacitors, the multi-phase operation has also been proved to gain the robustness on the flying capacitor mismatch. A demonstration PCB has been made to show the experimental results. The peak efficiency was captured at 40V-1.8V/4A with a number of 92.4%.

Secondly, an auxiliary circuit assisted Zero-Voltage-Switching 3-Level Buck (ZVS-3LB) converter is introduced in Chapter.4 with its fundamental operations, design analysis and key experimental results. By inserting an auxiliary ZVS circuit with around 20% area overhead, the converter achieves maximum 30% loss reduction compared with a conventional 3-level buck converter when the output current is below 1.5A. A peak efficiency of 92.4% is reached for 20V/5V conversion at 1A load. As another significant benefit, ZVS operation allows the switching frequency to reach a multiple Mega-Hertz range as a result of low switching loss, making the topology a good candidate for minimizing inductor usage.

Furthermore, an Integrated Transformer-less Stacked Active Bridge (ITSAB) converter that uses only nano-Henry scale inductors at 2-5MHz switching frequency is proposed in Chapter.5. Since it is derived from a Dickson-Star Switched Capacitor converter, the proposed converter inherits the benefit of low voltage stress on switches while enjoying an efficient fine regulation by phase shift, similar to a Dual Active Bridge (DAB) converter. The converter is optimized, designed and fabricated in 1.7mm*1.9mm area of a 130nm BCD process. The active die is flip-chipped on a 6.5mm*6.5mm package substrate together with power capacitors and two 10nH IPD inductors for demonstration, illustrating the feasibility of passive components integration, resulting in a peak efficiency of 91.2% and a peak power density of 1.36W/mm3 from 9.6-12V input to 2.15-3.3V output. Another demonstration is constructed on the same package substrate but with discrete air-core inductors. It achieves a peak efficiency of 92.4% and a peak power density of 0.62W/mm3, while delivering a max power of 7.5W. To achieve the performance, a detailed loss analysis and a unique optimization methodology for the converter, together with the design of key sub-blocks, including gate drivers (GDs), phase shift modulator (PSM), and ramp generator (RG), are provided in this chapter.

Additionally, a revised prototype of ITSAB converter that is capable of higher output current is presented in Chapter.6. It has been demonstrated 5.2A output current with 10nH inductors. The chip is fabricated with the same technology. The necessary techniques to achieve such high output current, including the 3D integration and switch partitioning, are addressed.

In last, a conclusion and future works, such as CC-CV mode, bidirectional conversion are presented.