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In this paper a novel digital controller and modified buck converter for improving heavy-to-light load transient response of low-power low-voltage dc-dc converters is introduced. The system is primarily designed for point-of-load (PoL) converters providing low regulated voltages for digital loads. In conventional buck topologies, the low output voltage, often below 1 V, severely limits the inductor current slew rate during the transients. To overcome this physical limitation, a modification is introduced whereby during heavy-to-light transients, the inductor current is, by the means of two extra switches, steered into the source and at the same time, the slew-rate of the current is significantly increased. The steering action is governed by a digital controller. The effectiveness of the system is verified on an FPGA-controlled, 12 V to 0.9 V, 10 W, experimental prototype. The results show that the steered-inductor digitally controlled buck converter has much shorter settling time and provides 2.8 times smaller overshoot than the conventional buck.
Date of Conference: 15-19 June 2008