應用於低功率物聯網產品具有飛跨電容自適應平衡技術之三階直流-直流降壓轉換器

Abstract

隨著超高速網路以及物聯網概念的普及興盛，越來越多的物聯網手持式裝置和感測器設備應運而生。為了降低產品設備的整體能耗，提高內置鋰電池的使用時間，需要直流-直流降壓轉換器模組以實現供電鋰電池到低功率物聯網整合晶片的能源傳遞。傳統的基於開關切換模式的二階直流-直流減壓轉換器需要採用耐高壓功率元件以因應互補金屬氧化物半導體先進製程之考量，提高了產品成本。相較之下，其三階直流-直流轉換器具有更小的紋波電壓，更低的紋波電感電流，功率開關元件的閘極驅動電壓減半等特性，因而能提供更低雜訊的輸出電壓，降低電流連續傳導模式之下界，且減少了關於先進製程的限制考量。然而由於制程變異和開關元件寄生效應等因素，三階直流-直流轉換器的飛跨電容存在電壓不平衡問題以及開關元件導通不穩定問題。本論文提出的三階直流-直流轉換器針對飛跨電容的穩壓問題進行分析比較，並提出更加理想有效的解決方案，在更廣的負載範圍內避免了三階向二階退化對之情況發生，且對三階轉換器電路進行改良設計以確保功率開關之導通關斷穩定。

With the popularity of ultra-high-speed Internet, the concept of Internet of things (IoT) has become a trend of development for future technology. Therefore, more and more Internet of Things portable devices and sensing applications are indispensable to human beings’ life. For the purpose of the energy saving of these products and prolonging the usage time of the internal batteries, DC-DC step-down converters are adopted to achieve the energy transfer between the energy supply and the low power integrated circuit for IoT applications. The conventional two-level DC-DC buck converters must introduce high voltage Power MOSFETs considering needs of the advanced process, which increases the cost. On the contrast, the three-level DC-DC buck converters have the advantages of lower output ripple, lower inductor current ripple and halving the gate driving voltages, which produces smaller output voltage ripple, lowers the current boundary from CCM to DCM with less restriction to the cost and process. However, the flying capacitor unbalancing problems and gate driving issues happen due to the process variation or parasitic effect. In this thesis, an analysis of pointed out flying capacitor unbalancing issue is discussed and a three-level buck converter with effective flying capacitor adaptive balancing (FCAB) technique is proposed. Moreover, an improvement is made to guarantee the normal operation of switches with the switching guarantee circuit. In a word, with the FCAB technique, the proposed three-level buck is more robust without degeneration to two-level one in a wide load range from 30mA to 200mA.