直流-直流降壓電源轉換器單晶片補償技術

Abstract

本文主要於較深入討論應用在直流-直流降壓電源轉換器的單晶片補償技術，其中直流-直流降壓電源轉換器的控制方法一般可以分為電壓模式控制及電流模式控制，一般而言，直流-直流降壓電源轉換器的補償電路都需要外掛元件如大電容得到期望的零點位置而使系統可以穩定。 關於電壓模式控制的直流-直流降壓電源轉換器，通常使用型式三的補償電路以增加迴路增益的交越頻率而得到較好的暫態響應，型式三的補償電路多半是由一個主動元件如運算放大器或者是運算電導放大器以及外接的大電容和電阻完成，對於型式三的補償電路的了解可以對於單晶片的比例積分微分控制器的設計提供很好的基礎，整合型的單晶片比例積分微分控制器使用四個運算電導放大器產生兩個零點以補償電壓模式控制的降壓電源轉換器產生的雙極點系統可以穩定，電路的結果證明單晶片的比例積分微分控制器和型式三的補償電路的表現是相同的。 至於電流模式控制的直流-直流降壓電源轉換器，其優點在於使用比例積分控制器即能使系統可以穩定，以補償的角度而言，這個好處是很明顯的，然而，比例積分控制器仍須使用外接的大電容，這還是在晶片整合上形成障礙，於是對單晶片的電流模式密勒補償及時間模式密勒補償電路有進一步的介紹、分析及實現，單晶片的電流模式密勒補償利用電流對可以整合在晶片上的小電容充放電的密勒效應而得到等效大電容值，單晶片的時間模式密勒補償則利用電路取樣原理在非常短時間內對誤差訊號作積分而得到整合在晶片上的小電容值等效放大，電路的結果證明單晶片的電流模式密勒補償及時間模式密勒補償的效能非常接近。

This work is discussing the comprehensive concepts of on-chip compensation (OCC) techniques for DC-DC buck converters with voltage mode control and current mode control. In general, the compensator network of DC-DC buck converter needs the external components for the large value capacitors to place the zeros in desired location to stabilize the system. Thus, the compensation of the regular DC-DC converter is completed by an off-chip compensator. Regarding DC-DC buck converter with voltage mode control, Type III compensator is usually employed to extend the loop gain crossover frequency for better transient response. Type III compensation is often implemented by a single active element such as an OPA or OTA with off-chip large capacitors and resistors, and its insight of compensation provides the fertile background to develop the counterpart PID OCC. The integrated PID OCC takes four OTAs for the creations of two zeros to compensate the double poles from buck converter with voltage mode control. The simulation results show that the performance of PID OCC is comparable to that of Type III off-chip compensation. As to DC-DC buck converter with current mode control, the advantage is that PI compensator is sufficient to manage the stability issue. The simplicity is obvious from the compensation point of view. However, the large capacitor required for PI compensator remains the problem to its integration on chip. Current mode Miller (CMM) OCC and time mode Miller (TMM) OCC is therefore introduced, analysed, implemented and simulated. CMM OCC by definition utilizes current to charge and discharge the small on-chip capacitor achieving the Miller effect for the large equivalent capacitance. On the other hand, TMM OCC makes use of sampling and hold to integrate the error information within very short period of time, and thus the capacitance amplification of the small on-chip capacitor is obtained. According to simulation results, the performance of CMM OCC and TMM OCC is compatible with current mode control buck converter.