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This paper presents a new enhanced V2-type constant on-time control architecture with digital implementations for solving the ripple oscillation issues when using small ESR capacitors in a buck converter. Instead of directly sensing the inductor current, an inductor current ramp estimator with the drift compensation is proposed as adding a virtual ESR ripple to the output voltage ripple. Only the input and output voltages are required to be sampled for the current ramp estimation. Hence the sampling-rate requirements for the analog-to-digital converters (ADCs) in the digital implementations are not critical. The limit-cycle oscillations due to the sampling effects can be improved by using the estimated current ramp with compared to the direct current sampling. Besides, the small-signal modeling of the digital enhanced V2 control architecture can provide the design guideline for choosing the current feedback gains. The effectiveness of the proposed control architecture and the current ramp estimator has been verified with simulation and experimental results.
Date of Conference: 12-16 Sept. 2010