Non-linear control of current-mode buck converter with an optimally scaled auxiliary phase

The main goal of this work is to de-couple the well-known efficiency/dynamic-response trade-off involved in scaling the inductance in dc-dc converters. This is achieved by introducing a low-cost auxiliary phase having an optimally scaled-down inductor and power-stage. The auxiliary phase is activated by a digital non-linear controller only during large transient events and thus does not affect the efficiency. An experimental 1 MHz, 10 V to 3.3 V current-mode buck converter prototype achieves a settling time below 2µs and a voltage drop of 50 mV (limited by Rc) for ΔIout=1 A, with an output capacitance of only 10 μF. A robust method was used for detecting the zero crossing of vc(t) and it is shown that if the auxiliary inductor is optimally scaled, charge balancing can easily be achieved for a range of load-steps.