一毫安培至三安培間效率80%之雙相位自適應導通時間降壓型轉換器採用被動式斜坡調變與電流感測技術

Abstract

此論文提出一個寬負載電流範圍帶有高效率之雙相位降壓型轉換器採用被動式斜波調變自適應導通時間控制，此控制架構會將責任週期傳入低通濾波器並產生被動式斜波，此外降壓型降轉換的輸出電壓成分也會被加入至被動斜波當中，此優點為迴路轉移函數會類似一個電流模式控制且負載電流暫態響應會被加速，然而，當負載電流減少的時候會將降壓型轉換器轉變為不連續導通模式，此控制架構將會轉變為輸出電壓夾鉗之切換頻率降低模式，降壓型轉換器的輸出電壓會被夾鉗且會直接當作調變斜波，此降壓型轉換器將會變成一個類似漣波自適應導通時間控制。 重載時，系統將會根據負載電流的大小去調整相位數目，根據上述討論，所提出的目標需要一個電感電流感測電路且帶有低感測誤差的特性，此論文所提出的被動式平均電感電流感測之斬波式誤差抵銷轉導放大器擁有低誤差感測、低功率消耗與無額外時脈的特性，此技術會被應用在相位調變與電感電流平衡。對於相位交錯來說，所提出的可預測式相位交錯結合自適應導通時間的特性，此技術的優點為電路再利用、低功率消耗、無額外時脈與低面積，根據上述的技術，所提出的被動式斜波調變自適應導通時間控制之輸出電壓夾鉗之切換頻率降低模式將會自動減少切換頻率去降低控制器的靜態電流使得在輕載時轉換效率提高，在重載時，相位調變偵測負載電流的大小去開啟奴隸相位去增加轉換效率，此電路透過上述技術達到寬負載電流範圍的雙相位降壓型轉換器。 本文所提出之雙相位降壓型轉換器採用台積電0.18μm且佔據晶片面積1.242mm2，此晶片包含功率電晶體、驅動器與控制器，雙相位降壓型轉換器操作在單相位切換頻率為6MHz且輸出電壓穩定在0.4V至1.5V從輸入電壓1.6V至2.0V而來，負載電流範圍1mA至3A內皆有80%以上的轉換效率，最高效率在負載電流為0.3A達到95.58%，當負載電流暫態響應發生的時候，兩個相位會立即打開去對輸出電壓充電，當負載電流1mA上升至3A時，輸出電壓掉落87mV，此外在最小的負載電流1mA下，控制器的靜態電流達到22.79μA。

A dual-phase buck converter with high efficiency loading current range using passive ramp modulation adaptive on-time control (PSRAOT control) is proposed. This control architecture will pass the duty cycle into the low-pass filter and generate the modulation ramp. In addition, the output voltage of the buck converter will also be added to the modulation ramp. The advantage is that the loop gain transfer function will be similar current mode control and the loading current transient response will be accelerated. However, when the loading current decreases to turn the buck converter into discontinuous con-duction mode (DCM), the control architecture converts to output voltage clamping with switching frequency reduction mode (OVCSFR mode). The output voltage of the buck converter will be clamped and it will be directly used as the modulation ramp. The buck converter will be a ripple-based adaptive on-time control (RBAOT control). In the heavy loading current, the system will adjust the number of phases according to the loading current. As discussed above, the proposed target requires an inductor current sensing with a low sensing error. In this paper, the passive average inductor current sense with chopper offset cancellation Gm amplifier is proposed, which has the characteristics of low sensing error, low power consumption and external clockless. This technique will be applied to phase shedding and inductor current balance. With regard to phase interleaving, the proposed predictive phase interleaving incorporates the circuit characteristics of adaptive on-time control. This technique has the characteristics of circuit reuse, low power consumption, external clockless and low area. According to the above techniques, the proposed PSRAOT with OVCSFR mode will decrease switching frequency to reduce the quiescent current of the controller and the conversion efficiency will increase in light loading current. Phase shedding will detect the size of the loading current and it will turn on the slave phase to increase conversion efficiency in heavy loading current. The proposed dual-phase buck converter applies above techniques to achieve wide range efficiency. Fabricated in a TSMC 0.18μm CMOS process, the prototype dual-phase buck converter occupies 1.24mm2. The chip contains power MOS, driver and controller. The buck converter operates 6MHz of switching frequency at a single phase and regulates output voltage to in the range of 0.4V to 1.5V from 1.6V to 2.0V input voltage. The conversion efficiency is above 80% between the loading current range of 1mA – 3A and the maximum conversion efficiency is 95.58%. When the loading current transient occurs, the two phases can be instantly fully opened for charging output voltage. With a 1mA to 3A step in the loading current, the undershoot voltage is 87mV. In addition, the quiescent current of the controller is 22.79μA at the lightest loading current of 1mA.