Online Controller Tuning in Current Mode Adaptive Off-Time Digital Control: A Large-Signal Approach

Constant off-time control offers fast transient recovery and inherent current-loop stability for wide duty ratio operation; however, it suffers from poor step-down transient and requires constant time-adaptation for improved performance. In addition, the existing small-signal based tuning methods restricts the achievable closed-loop bandwidth especially in non-minimum phase converters. This paper introduces a geometric based non-linear tuning method for constant OFF-time digital modulation without the requirement of linearized small-signal model. The automated (constant) time adaptation method for improved performance is developed with minimum hardware resources, which achieves time-optimal transient recovery with single switching action. The mono-shot counter can be updated in real-time using a time-to-digital converter for a fixed-frequency operation, without the need of the input voltage sensing. The method of time-optimal tuning with automated time-adaptation is extended for constant ON/OFF-time hybrid modulation technique. A boost converter prototype is made and the proposed tuning with adaptive OFF-time is realized using a FPGA device and an improved performance are demonstrated using test results.