Design methodology of a non-invasive sensor to measure the current of the output capacitor for a very fast non-linear control

The combination of non-linear control and linear control proposed in [1] has a very fast transient response (voltage step from 1 V to 1.5 V in 2 mus). In order to achieve this fast transient response the non-linear scheme is based on measuring the current of the output capacitor of a Buck converter. The design of this current sensor is complex due to parasitic effects such as component tolerances (bandwidth and dc gain of the Op-Amp), aging, temperature variation, etc. A design methodology for this current sensor is proposed regarding all these effects. The sensing circuit is designed to mirror the actual capacitor current with a trans-impedance amplifier by matching phase and scaling impedances of the RLC network (C, ESR and ESL of the output capacitor). The proposed methodology has been validated by means of a buck converter switching at 5 MHz. Experimental results validate that the current sensor behaves appropriately under voltage and load steps.