具高效率依載跳頻與綠能模式控制之三分之一倍電容幫浦式直流降壓轉換器

Abstract

近幾年來，可攜式電子產品發展迅速，因此電源管理系統扮演著非常重要的角色，它不單只是提拱一個穩定電壓源給予晶片系統使用，更必須具備高效率能量轉換以及快速反應之特性。在傳統的電容幫浦電壓轉換器中，使用較大的輸出電容與幫浦電容，因此佔去大面積，除此之外，也因為大電容所負帶的寄生電阻，會使得效率無法更加提升，因而不利以現今可攜式電子產品微行化的趨勢。本論文提出具有高效率自動依載跳頻與綠能模式控制的電容幫浦直流降壓轉換器，其最大的不同點在於使用比傳統式小十倍的輸出電容與幫浦電容。此外，為了能提拱一樣大瓦數的輸出負載下，隨著負載變大，切換頻率也因為依載跳頻技術的調整隨之變快，應而更能夠達到高效率、高品質的特性。這種依載跳頻技術是利用內建的虛擬時脈產生器與領先落後偵測電路來實現。並且在極輕載時，系統會進入綠能模式控制，當輸出能量不夠時，控制電路才會運作，反之，能量足夠時，就讓控制電路進入休息狀態，因而使得效率更加提升。本論文的晶片是使用五十五奈米的先進製程來實現的。在實驗結果中也證實了本論文所提出的使用小電容依舊可提供大負載變化，並且可達到80%的能量轉換效率以及低於30mV的高品質輸出電壓。

A normalized 98% efficiency 3.3V-to-1V switched-capacitor (SC) step-down DC-DC converter with load-dependent frequency hopping (LFH) and deep-green mode (DGM) operation is proposed for system-on-a-chip (SoC) application. According to output loading current, the LFH technique can immediately and dynamically adjust the switching frequency through the use of pseudo-clock generator (PCG) and lead-lag detector (LLD) circuit to obtain high power conversion efficiency and small output voltage ripple over a wide loading current range. Therefore, adequate loading current supplying function and output voltage regulation can be guaranteed. Moreover, the DGM operation, similar to pulse skipping mode, can mask the switching clock to reduce power loss at ultra-light loads for further improving power efficiency. The test chip fabricated in 55 nm CMOS process demonstrates that the proposed fast transient converter can deliver wide load range from 10 mA to 250 mA with two small flying capacitors (CF1,CF2=0.1μF) and one output capacitor (COUT=1μF). The peak conversion efficiency is 89% compared to the ideal value of 91% (3*VOUT/VIN). In other words, the peak normalized efficiency is equal to 98%. The overall normalized efficiency is always kept higher than 90 % while the output voltage ripple is guaranteed smaller than 30mV.