Integrating power inductors onto the IC -: SOC implementation of inductor multipliers for DC-DC converters

This paper introduces the technique of active inductor multiplier, whereby a small inductor is effectively multiplied to generate the effects of a large power inductor. Medium/High power dc-dc converters, which are essential power supply circuits in almost all portable applications, require off-chip inductors, which take-up significant PCB real estate, add cost, and impede SOC implementation. The inductor multiplier technique developed here makes it possible for large inductors to be integrated onto the IC, thus meeting the demands of mobile battery-powered applications and approaching SOC solutions. A 1.8 V, 2.5 A buck-converter for 2-cell Ni-Cd/NiMH (3.2-1.8 V) battery applications was simulated with and without the inductor-multiplier. An inductance of 150 nH was effectively multiplied to 1.5 muH, giving the same ripple performance. Efficiency, however, was lower throughout the load current range with a 5 to 19% difference in the range from 5 to 1.5 A (efficiency was 74% at 2.5 A), but still better than what a linear regulator would have yielded (less than 70%).