On-chip inductor DCR self-calibration technique for high frequency integrated multiphase switching converters

Phase current imbalance could cause hazardous hot spots and severe heat distribution issues in integrated multiphase converters. Targeting at one most significant cause of phase current imbalance — inductor DC resistance (DCR) mismatch, this paper presents an online self-calibration technique that detects the DCR mismatch and calibrates the phase average inductor currents automatically. The circuits associated with the technique add ignorable power and silicon cost to the system, but balance phase currents effectively and precisely. The technique is verified in a four phase current-mode hysteretic controlled buck converter that is designed in a 0.35μm CMOS process. The converter delivers 9.6W peak power with a maximum chip power density of 5W/mm2 and a peak efficiency of 87.2% at 10MHz. At a nominal load of 4A and with ±20% industrial standard L and DCR mismatches, the proposed technique reduces the maximum phase current imbalance from 460mA to 25mA and improved the efficiency by about 1%.