Parameter-Insensitive Mixed-Signal Hysteresis-Band Current Control for Point-of-Load Converters With Fixed Frequency and Robust Stability

The inductor current ripple under hysteresis current control is sensitive to system as well as controller parameters, which often deviates from the desired band. Thus, a phase-locked-loop (PLL) is employed to regulate the switching frequency over the operating range. Digital platform drastically simplifies this using an all-digital PLL (ADPLL) and offers the controller-tuning flexibility for improved performance. However, the use of uniform voltage-sampling often leads to multilimit cycle instability. This paper proposes a mixed-signal hysteretic current controller (MSHCC) with the digital voltage-loop and the analog current-loop. A digital-to-analog converter is sufficient to generate time-multiplexed current references. This achieves robust stability and parameter-insensitive current ripple by sampling the error-voltage at the rising edge of the high-side gate signal. Stability analysis is carried out using discrete-time models. The proposed MSHCC can be configured to either of the peak, average, or valley current-mode techniques along with the flexibility to adjust the switching frequency using an ADPLL for real-time energy-optimization. The proposed scheme is implemented using an FPGA device and tested on a buck converter prototype. The MSHCC scheme can be extended to a multiphase buck converter.