Mixed-Signal Peak Current Mode Control of a Buck Converter

ICT applications such as cloud computing in data-centers, Internet of Things, mobile communication (5G), automotive, and Artificial Intelligence drive the needs for increased data processing capabilities of modern microprocessors. In the automotive industry one of the major trends is the increasing number of complex electric and electronic systems in a car that need a significant number of microcontrollers. In order to assure proper functioning and optimum performance, a microcontroller must be supplied with the correct amount of current, demanded by its cores and other digital circuits. Moreover the supply voltage must be kept as close as possible to a desired value even during fast variations of the current. Buck topology Point-of-Load converters are employed to deliver the proper power to microcontrollers. The advancement in complexity and speed of modern microcontrollers has made the design of their power supply control systems very challenging. Traditionally, DCDC converters relied on analog controllers because of simplicity of implementation and excellent dynamic performance. However continued rapid advances in CMOS and VLSI technology have enabled the development of a high-performance, practical, cost-effective, and low-power digital controller. The mixed-signal approach brings some benefits from both the digital domain, such as programmability, integration and ability to implement sophisticated control, and the analog domain like inherent current protection, low audio susceptibility and fast current dynamics. Alongside the advantages there are also some drawbacks such as the need of current sensing and limit-cycle oscillations due to quantization and sampling frequency. This work will focus on the analysis, modelling and simulation of mixed-signal peak current mode control of a synchronous Buck Converter. In this control technique, the outer loop, responsible for the output voltage, is implemented in digital domain using an ADC and a digital PI compensator. On the other hand, in the inner current loop, the comparison between the sensed inductor current and the peak modulation signal is performed in the analog domain. The current comparator and RS latch, which generates the PWM signal, completes the control loop. The peak current modulation signal is generated by the digital compensator and then it is converted in an analog signal by means of a Digita-to-Analog Converter (DAC). Different current sensing techniques will be considered for this purpose, highlighting their pros and cons and evaluating their feasibility for a specific application.