This paper proposes a wide output range and tri-mode BUCK circuit which utilizes PWM mode, PFM mode and PSM mode at heavy, light and very light loads respectively. By shutting down the majority of the internal modules, employing minimum loop control and reducing the quiescent current, the design could lower the static power consumption. The work, therefore, could increase efficiency at very light load. The proposed BUCK is fabricated using SMIC 0.18 µm process. Test results show that when the

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... put is 4 V and the output is 1.8 V, the efficiency of the proposed BUCK is 90% and 85% at 300 mA and 5 mA load current respectively.