Efficiency estimation in digitally-controlled dc-dc buck converters based on single current sensing

This paper proposes an efficiency estimator for dc-dc buck converters suitable for on-chip integration in the digital IC controller. The proposed solution is tailored for distributed power architectures, where the on-line efficiency measurement or estimation of each dc-dc converter is useful in order to perform a system power management and to monitor the status of each point of load (POL) converter. Existing solutions relay on the measurement of the input voltage and current, output voltage and current, the latter usually based on the output inductor current sensing (at least for buck-type converters). The current sensing is the main drawback since it requires two current sensors and, more importantly, a precise matching, tuning and temperature compensation in the two current sensors. This paper proposes an indirect estimation of the ratio between the output and input current based on a single current sensing, thus avoiding precise gain tuning. The current sensing is based on the input bus voltage and a filter matched with the impedance seen by the dc-dc converter. Experimental results on a synchronous buck converter with the efficiency estimator implemented in a field programmable gate array (FPGA) show the properties as well as the limitations of the proposed method.