Hysteresis-Based Mixed-Signal Voltage-Mode Control for dc-dc Converters

This paper investigates a mixed signal voltage-mode controller for dc-dc converters based on hysteresis modulation. In the proposed control architecture both switch turn-on and switch turn-off instants are determined asynchronously by comparing the converter output voltage to the voltage ramp driven by the digital control using a digital-to-analog converter (DAC). Under the dynamic point of view, the achievable performances resemble those of a multi-loop control with an internal hysteresis current control based on the estimated inductor current. Moreover, the switching frequency is kept constant under steady-state conditions by modulating the amplitude of the DAC ramp. The proposed control features good dynamic performance, frequency modulation during transients and low-complexity, since it requires a DAC, a comparator and, more importantly, low signal-processing requirement. Simulation and experimental results on a synchronous buck converter, where the digital control has been implemented in a field programmable gate array (FPGA), are also reported.