An Integrated Speed- and Accuracy-Enhanced CMOS Current Sensor With Dynamically Biased Shunt Feedback for Current-Mode Buck Regulators

This paper presents a new compact on-chip current-sensing circuit to enable current-mode buck regulators operating at a high switching frequency for reducing the inductor profile. A dynamically biased shunt feedback technique is developed in the proposed current sensor to push nondominant poles to higher frequencies, thereby improving the speed and stability of the current sensor under a wide range of load currents. A feedforward gain stage in the proposed current sensor also increases the dc loop-gain magnitude and thus enhances the accuracy of the current sensing. A current-mode buck regulator with the proposed current sensor has been implemented in a standard 0.35-μm CMOS process. Measurement results show that the proposed current sensor can achieve 95% sensing accuracy and <;; 50-ns settling time. The buck converter can thus operate properly at the switching frequency of 2.5 MHz with the duty cycle down to 0.3. The output ripple voltage of the regulator is <;; 43 mV with a 4.7-μF off-chip capacitor and a 2.2-μH off-chip inductor. The power efficiency of the buck regulator achieves above 80% over the load current ranging from 25 to 500 mA.