Unpredictable continuous conduction mode switching frequency variation that occurs commonly in ripple-based control can lead to serious electronic-magnetic interface noise problems and thus increase the effort required for designing noise filters. Sensorless load current correction and dynamic tolerance window techniques are proposed in this paper to reduce the frequency variations caused by conduction losses without employing complicated circuits such as phase-locked loop or current sensors. The proposed dc-dc buck converter with input voltage ranging from 2.7 to 3.6 V and an output voltage between 1.0 and 1.2 V was fabricated using a standard 0.18-μm CMOS process, and the converter achieved excellent adaptive voltage positioning function. Experimental results show that the switching frequency variation improved approximately 60% over traditional techniques in constant on-time control when the load current was changed from 150 to 1000 mA. The measurement results also show that frequency variation across the entire input/output and loading ranges was lowered to only ±2.6%. The maximum power efficiency was 88.2% at 150 mA with an input voltage of 2.7 V.
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