A Wide Load Range and High Efficiency Switched-Capacitor DC-DC Converter With Pseudo-Clock Controlled Load-dependent Frequency

Abstract

A high efficiency 3.3V-to-1V switched-capacitor (SC) step-down DC-DC converter with load-dependent frequency control (LFC) and deep-green mode (DGM) operation is proposed for system-on-a-chip (SoC) application. According to output loading current, the LFC technique can immediately and dynamically adjust the switching frequency through the use of pseudo-clock generator (PCG) and lead-lag detector (LLD) circuit to obtain high power conversion efficiency and small output voltage ripple over a wide loading current range. Therefore, adequate loading current supplying function and output voltage regulation can be guaranteed. Moreover, the DGM operation, similar to pulse skipping mode, can mask the switching clock to reduce power loss at ultra-light loads for further improving power efficiency. The test chip fabricated in 55 nm CMOS process demonstrates that the proposed fast transient converter can deliver wide load range from 10 mA to 250 mA with two small flying capacitors (C-F1, C-F2 = 0.1 mu F) and one output capacitor (C-OUT = 1 mu F). The peak conversion efficiency is 89% compared to the ideal value of 91% (3 * V-OUT/V-IN). In other words, the peak normalized efficiency is equal to 98%. The overall normalized efficiency is always kept higher than 90% while the output voltage ripple is guaranteed smaller than 30 mV.