A 12/24 V-to-sub-1 V Double Step-down Converter with Dual-ramp Control for VCF Balancing and Fast Transient Response

In data centers and artificial intelligence supercomputers, power supplies are urgently needed to offer high conversion ratio with high efficiency and fast transient response. Current solutions struggle to achieve both high efficiency and fast transient response, simultaneously. This paper introduces a novel Double Step-down (DSD) Converter featuring a dual-phase ramp for 12/24 V-to-sub-1 V conversion. The impact of flying capacitor voltage VCF deviation on DSD converters are analyzed and a dual-ramp control architecture is proposed to alleviate VCF deviation, thereby enhancing system robustness. Additionally, we propose a novel approach of leveraging high-frequency pulse injection to suppress undershoot and introduce a discharge path to mitigate overshoot, thereby the transient characteristics of converter are significantly improved. By seamlessly integrating low-frequency steady-state control with high-frequency transient enhancement control, this work successfully overcomes the conventional bottleneck of balancing high efficiency and fast transient response. The most distinctive feature is that the proposed dual-ramp and transient enhancement synergy achieves VCF balancing during both steady-state and transient responses. A prototype is implemented with a 0.18-μm Bipolar-CMOS-DMOS (BCD) technology, achieving high power efficiencies of 92.2%, 89.1%, and 83% at frequencies of 250 kHz, 500 kHz, and 1 MHz, respectively. During a load transient of 1.49 A / 300 ns, the undershoot and overshoot are reduced to 280 mV and 160 mV, respectively, and the corresponding response times are 20 μs and 12 μs, respectively. Measurement results highlight the synchronous enhancement in both efficiency and transient response achieved by the proposed method and topology.