A High-Light-Load-Efficiency, Low-Ripple-Voltage PFM Buck Converter for IoT Applications

A very high-light-load-efficiency, low-ripple-voltage pulse-frequency modulation (PFM) buck converter for IoT applications is presented in this paper. The PFM buck converter is widely used because of its higher light-load efficiency. However, it has a higher ripple voltage than its pulse-width modulation counterpart. Although the ripple voltage of a PFM buck converter can be reduced by increasing the output capacitance, we find that this leads to a decrease in the light-load efficiency due to increased controller loss. This problem is analyzed and verified by IC measurements in this work. The proposed PFM buck converter remarkably reduces the controller loss even at low ripple voltages by replacing the static comparator with a dynamic comparator, which provides a high voltage gain, fast evaluation speed, and low power consumption. In addition, to further reduce the controller loss, a dynamic shut-down control method, which selectively turns off control circuits, is used. The proposed PFM buck converter was fabricated with 0.35 m CMOS technology. The magnitude and variation of the output ripple voltage are 3 and 2 mV, respectively, and the light-load and peak efficiencies are 81.1% and 94.8%, respectively.