Constant Off-Time-Based Current-Balancing Technique With Accuracy and Transient Optimization in Wide I/O Range for Multi-Phase Regulator

A constant off-time (COFT) based current-balancing (CB) technique is proposed for integrated multi-phase DC-DC switching regulators with wide input/output (I/O) voltage range. The small-signal characteristics and design criteria of the proposed technique are derived based on describing functions. The current-balancing accuracy of the proposed technique depends merely on the ratio between the sensing FETs and the corresponding power switches ( $\alpha $ ), while the requirement on absolute equivalent sensing-resistances ( $R_{\mathrm {i}}$ ) and the matching of sensing circuits among phases are relaxed. Meanwhile, both the proposed current-balancing behavior and the adjustment of phase number will not affect the stability and the transient behavior of the multi-phase system. Furthermore, as a crucial block of the COFT control scheme, the proposed self-tuning PLLs of clock synchronization loop can remain fixed bandwidth under different I/O voltages, which further enhance the system stability. Therefore, in principle, the phase-interleaving with fixed switching frequency can be realized without the limit of duty cycle. As a result, the proposed CB technique can alleviate the stringent matching requirement of layout in conventional multi-phase systems, as well as the loop compensation difficulty. It is verified by an integrated dual-phase regulator fabricated in a $0.18\mu $ m BCD process. Experimental results show that the regulator can provide 0.9-1.8V output from a 2.3-5.5V input at both steady state and load-transient state with significantly higher performance by the proposed CB technique, ensuring current-imbalance ratio within ±1.3%.