適用於氮化鎵同步整流降壓型轉換器之具有可調式空白時間控制及電荷共享式靴帶電路之閘極驅動積體電路

Abstract

近年來，高切換頻率之降壓型轉換器被廣泛應用於各式各樣的電子消費性產品中。高切換頻率轉換器有許多優點包括更高的功率密度、更快速的暫態響應。氮化鎵元件因為其材料特性，比起傳統矽元件更適合應用在高切換頻率的轉換器應用上，然而氮化鎵元件的閘極驅動存在挑戰。本論文提出一適合增強型氮化鎵電晶體的閘極驅動積體電路，並且實現一切換頻率10MHz，輸入電壓12V，輸出電壓5V的降壓型轉換器。論文提出一個可調式空白時間控制的方法以及具有電荷共享的靴帶電路架構。可調式空白時間控制被應用於消除逆向導通時所造成的功率損失以及避免上橋開關與下橋開關同時導通所造成的突波電流發生。具有電荷共享的靴帶電路架構被應用於確保提供足夠的閘極驅動電壓，核心概念為運用一個高壓的電容去儲存更多的電荷，以確保開關打開時，維持足夠高的閘極驅動電壓給功率元件。本晶片由台積電0.25um BCD製程實現，提出一適合增強型氮化鎵電晶體的閘極驅動積體電路，並在輸出從輕載到重載的情況下可將最小空白時間控制在0.4ns到0.45ns之間。相較於傳統的空白時間控制法，在重載情況下可提升4%的轉換器效率。除此之外，利用晶片上的低壓靴帶電容100pF以及高壓靴帶電容60pF和低壓箝位電容40pF，可以讓整體的驅動電壓的掉壓值小於0.6伏特。相較於傳統的靴帶電容作法，只需要原本50%的面積，即可達成相同驅動電壓的掉壓。

In recent years, high switching frequency buck converters are widely used in consumer electronics applications. High switching frequency converter has advantages such as higher power density and faster transient response. Comparing to traditional silicon devices, GaN devices are more suitable for high switching frequency applications due to the material characteristic. However, there are challenges in GaN gate driving. This thesis proposed a gate driver IC for enhancement-mode GaN and implemented a 12V-to-5V buck converter with 10MHz switching frequency. This thesis proposes an adaptive bang-bang dead-time control and the charge sharing bootstrap circuit. The adaptive bang-bang dead-time modulator is used to eliminate the power loss caused by reverse conduction and prevent high side and low side switches shoot-through. The charge sharing bootstrap circuit is chosen to ensure sufficient gate overdrive voltage. The key idea is using an HV capacitor to store large energy, which can be supplied to power switch and charged to a higher voltage. Fabricated in a TSMC 0.25-μm Bipolar-CMOS-DMOS process, the proposed GaN driver integrated circuit (IC) enables buck converter to operate at 10MHz switching frequency and adjust minimal dead-time to as low as 0.4 ns to 0.45 ns under light load and heavy load condition. Compared with fixed dead-time control, proposed work improves 4% efficiency under 1A condition. The fully integrated bootstrap circuit with 100pF and 60pF (HV) capacitor and 40pF (LV) clamp capacitor can get the expected voltage drop of lower than 0.6V. Both bootstrap capacitors require 50% less area compared to a conventional bootstrap circuit.