Buck Converter With Load Adaptive Losses and 256x Sub-mW Load Transient Response Time of 0.8 ms Using Synchronous Control

The authors propose a pulse-frequency modulation based buck converter that uses synchronous control. The controller clock continuously tracks twice the switching frequency through internal control that employs a primary clock. The system responds to 256x load rise transients within four switching periods using synchronous control to have fine output voltage attributes with a 27 nF-capacitor at output. Zero current switching in ≤10 ns is achieved using an active diode (AD). Employment of the AD ensures nonoverlap conduction of the switches in the buck converter. The analog AD-controller operates bias-free and the power consumed by it scales with switching frequency. As the average switching frequency is proportional to load, the losses in the main controller and AD-controller scale with load that improves the efficiency at light load. The system fabricated in 180 nm CMOS technology for 1.2 V output voltage, enhances the state-of-the-art transient response rate in synchronous mode (to 2.6–657 μA in 812.8 μs) for limiting the voltage droop to 7 mV. Peak efficiency achieved is 94.8% at 788 μW output. Efficiency >80% is obtained for the minimum output power levels of 12.4 μW and 1.75 μW at primary clocks of 1.25 MHz and 1.25/32 MHz, respectively.