High-performance synchronous-asynchronous digital voltage-mode control for dc-dc converters

This paper investigates a mixed synchronous/asynchronous digital voltage-mode controller for dc-dc converters. In the proposed control architecture the turn-on switching event is determined asynchronously by comparing the converter output voltage and a synchronously generated voltage ramp driven by the digital control using a low-resolution Digital-to-Analog Converter (DAC). Switch turn-off is determined synchronously by the system clock. In the proposed approach, the derivative action of the Proportional-Integral-Derivative (PID) voltage-mode controller is inherently obtained by the frequency modulation, without requiring the digital computation of the derivative action. A simplified small-signal model is also derived in order to analyze the performance achievable by the proposed solution. This control architecture features good dynamic performance, frequency modulation during transients and small quantization effects. Simulation and experimental results on a synchronous buck converter, where the digital control has been implemented in Field Programmable Gate Array (FPGA), confirm the effectiveness of the proposed solution.