Self-Oscillating Hysteretic DC-DC Controllers: From the Ground Up

State-of-the-art microprocessors as well as Digital-Signal Processing (DSP) circuits demand power supplies to be quick, accurate, and capable of delivering high currents. Additionally, portable battery-powered applications, like laptop computers, require these Integrated Circuits (IC's) to be power efficient to extend battery life. In terms of speed, which also translates to accuracy, of course, self-oscillating hysteretic DC-DC controllers are the fastest, not to mention one of the oldest, topologies around and, therefore, most appropriate for today's high performance applications. Historically, their advantage in speed has been offset by their inability to switch at constant pre-determined frequencies. In today's harsh load environment, however, speed and accuracy are paramount and yesterday's concerns are reevaluated, clearing the path for hysteretic controllers back into the marketplace. Portable electronics also demand these controllers to be integrated onto the same die, which present additional challenges forcing designers to be knowledgeable in both system and integrated circuit design issues. This talk will not only introduce and discuss the re-emergence of hysteretic controllers back into the marketplace but it will also deal with the practical issues of integrating the controller onto a single die. First, a brief highlight and a comparative evaluation of the alternate architectures will be presented. Operation of hysteretic converters will be analyzed, from an intuitive perspective to formalized steady-state and transient-response derivations. Variations of the controllers will ultimately be visited and evaluated. Integrated circuit design issues, such as noise injection, chiplevel layout considerations, and reliability/robustness concerns, will be highlighted. Performance-optimization techniques targeted to improve accuracy and speed will be illustrated and discussed. Towards the end, specific circuit designs for some of the major blocks, like the comparator and some of the sensing circuitry, will be presented while addressing their associated system challenges.