State Machine Based Inductor Current Estimation Technique for Digitally Controlled DC-DC Converter

Current sensing and its measurement feedback are essential for the implementation of current-mode controllers (CMC) for dc-dc converters. For digital implementation of such controllers, the sensed current output need to be sampled using an analog-to-digital converter (ADC) to serve as the controller closed loop feedback. Hence, the performance of the controller depends upon both the sensing method and also on characteristics of the ADC used. The sampling rate of the ADC plays an important role in the performance of the controller. With increase in dc-dc converter operating frequency, finding an ADC with an adequate sampling rate and reasonable price is a challenge. Current estimation is one such method that can avoid dependency on current sensors and expensive ADCs. This work presents the design aspects of an inductor current estimator for a dc-dc converter. The inductor current estimation depends on the physical properties of the inductor. Using a state-machine-based approach, the development of the current estimator is proposed and its FPGA-based implementation aspects are elaborated. The proposed estimator is tested using a laboratory prototype of a boost converter with current-mode control.