Characterization and performance comparison of digital V2-type constant on-time control for buck converters

This paper characterizes two digital V² control schemes using for the buck converters with small-ESR capacitors based on the presented small-signal models. Due to the sampling effects of the analog-to-digital converters (ADCs), the digital V² control system performances are not as good as the analog ones, even using the inductor current sensing feedback. The major issue is that in order to stabilize and to make the system well-damped, large external ramps or large current sensing gains are required. However, with such large ramp compensations, some benefits of the V² control architecture, including the fast transients and the easily compensation, will be vanished. In this paper, a hybrid-ramp compensation concept is presented to improve the system performance. Both small-signal modeling analyses and simulation verifications are given. And the load transient experimental results with different ramp compensations are also shown in this paper.