A buck DC-DC converter using automatic PFM/PWM mode change for high-efficiency Li-ion battery charger

We present a high efficiency buck DC-DC converter for switch-mode Lithium-ion (Li-ion) battery charger. To achieve a high efficiency over a wide load range, the converter enters a power saving pulse-frequency modulation (PFM) mode at light load currents. And the proposed buck converter features an automatic mode change between pulse-width modulation (PWM) and PFM depending on the load current level. The chip was fabricated in a 0.18 μm 1-poly 6-metal standard CMOS process in a 1.28 × 1.19 mm². The maximum efficiency is 93%.