A 95.4% Hybrid Always-Dual-Path Recursive Step-Down Converter Using Adaptive Switching Level Control With 288 mΩ Large-DCR Inductor

This article proposes a hybrid always-dual-path recursive (ADPR) step-down converter to achieve high efficiency using a small-volume inductor with large dc resistance (DCR). The ADPR step-down converter utilizes only low-voltage transistors (1.5 or 3.3 V) for power switches. The converter has adopted adaptive switching level control, which includes adaptive mode transition (AMT) and adaptive duty modulation (ADM), based on one dual-flipped saw-tooth waveform. AMT and ADM enable a wide range operation and ensure flying capacitor charge balance while leading to higher efficiency. In addition, a complementary switch guarantees the reliable operation at lower input voltage to 2.8 V. The 130-nm prototype converter used a small-volume 4.7 μH inductor with 288 mΩ DCR, a 10 μF output capacitor, and two 4.7 μF flying capacitors to verify highly efficient always-dual-path recursive operation. The measurement results show that the ADPR step-down converter can be suitable for converting Li-ion battery (2.8–4.2 V) to 0.7–1.1 V while the ratio of the inductor current over the load current (I_LOAD) can be set between 0.42 and 0.66 at all range. The peak efficiency was measured up to 95.4% at V_IN = 3.7 V and I_LOAD = 75 mA. When V_OUT = 1 V and I_LOAD = 100 mA, the efficiencies were higher than 92.9% at whole input voltage ranges, ensuring small efficiency variation of 1.6%.