You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review 
Chapter Title:  B. INTEGRATED DC-DC CONVERTERS 
1. Abstract of Cited Paper (BIB001):  kV-class GaN high electron mobility transistors built on low-cost Si substrate have been developed with proven switching performance. These devices show a blocking voltage >1200 V, low on-resistance 200 V/ns. A 3-kW 400 V:800 V hard-switched boost converter based on the GaN transistor achieves 99% efficiency at 100 kHz, well exceeding that of other competing semiconductors. 
2. Abstract of Cited Paper (BIB002):  Power switching devices based on wide bandgap semiconductor materials, such as silicon carbide (SiC) and gallium nitride (GaN) offer superior performance such as low switching and conduction losses, high voltage, high frequency, and high temperature operation. In this paper, a 600-V GaN switch and a 600-V GaN diode were tested in detail to understand the GaN device capabilities with respect to equivalent silicon-based devices such as IGBT and MOSFET. Detailed experimental loss models are developed and compared with datasheet models. Experimental setup of different power converters such as boost, buck-boost, and half-bridge inverter and associated comparative experimental results are presented. This paper also presents the investigations into the effectiveness of using GaN devices and higher switching frequencies in reducing the total size and cost of power conversion equipment such as an online UPS system.

Literature Review:
Achieving higher operation efficiency to reduce losses during power conversion is one of the key concerns in power DC-DC converters. The research groups and industry leading companies have first time switched to GaN solution to pursue higher performance. The discrete approach using discrete GaN switches has shown great improvement in converter operation frequency and efficiency. The controller, protector and driver are dedicated Si-based ICs, which are mounted on the same PCB with GaN switches and passive components. Since 2007, converters with GaN normally-ON HEMT as high-side switch and SiC-SBD as low-side switch have demonstrated efficiency up to 97.8 % at MHz range BIB001 . With normally-OFF HEMT as high-side switch, Transphorm realizes a 3kW, 99 % converter at 100 kHz BIB002 . When using GaN SBD as low-side switch, the converter shows an efficiency of 98.5 % at 500 kHz and 500 W condition BIB003 . Lots of works adopt normally-OFF half-bridge structure, the high efficiency of 98.8 % is realized at 50 kHz by University of Southern Denmark  and high output power of 3.3 kW is realized at 300 kHz by Fudan University  . These cases have substantially shown the advantages of GaN based discrete DC-DC converters. Further exploiting the properties of GaN devices, the road of integration starts. The integrated GaN converters are reviewed in terms of the fabrication technology of smart power IC platforms.