A Current-Mode-Hysteretic Buck Converter With Constant-Frequency-Controlled and New Active-Current-Sensing Techniques

Abstract

This article presents a hysteretic-current-controlled buck converter with constant-frequency-controlled and active-current-sensing (ACS) techniques. This converter used phase-frequency-locked techniques to achieve constant switching frequency. Even if the input voltage or output load current changes, the switching frequency will be as stable as possible at 1 MHz. The proposed ACS circuit will not generate sparks, so the current feedback loop does not need a sample-and-hold circuit, and that will reduce the transient response time. The proposed buck converter has been fabricated with TSMC 0.35 μm CMOS 2P4M technology; the total area of the chip is 1.5 mm × 1.5 mm. The measurement results of this buck converter show that the maximum power efficiency is 90% when the output voltage is 2.5 V and the load current is 300 mA. The output voltage range is 2.5-1 V, and the maximum load current is 600 mA. When the load current varies between 100 and 500 mA, the load transient response is 2.6 μs/2.2 μs and undershoot/overshoot is 20 mV/30 mV. The switching frequency of this buck converter is locked at 1 MHz and the voltage error is within 1%.