Abstract
Constant on-time (COT) controlled multi-phase buck converter has been widely used in high-current applications such as computing devices to achieve high entire-load-range efficiency. However, the literature lacks comprehensive analysis and design guide of the current-balance loop in COT control, resulting in possible low efficiency, per-phase current protection false-trigger, and stability issue. To solve the aforementioned issues, dc inductor current equations and small-signal models are proposed for COT control with the current-balance loop. Current-balance loop gain design guideline is then proposed to achieve accurate dc current balance and stability. Experiment and simulation results verify the analysis and the accuracy of the proposed models.
Highlights
Multi-phase buck converter with constant on-time (COT) control has been widely used in applications requiring lowoutput-voltage, high-current, and high entire-load-range efficiency such as computing devices and processors [1]–[8]
The contribution of this paper is to propose a comprehensive analysis and design guideline for multiphase buck converter with current-mode COT (CMCOT) control and current-balance loop
Current-balance control is achieved by sensing per-phase inductor current and adjusting per-phase on-time
Summary
Multi-phase buck converter with constant on-time (COT) control has been widely used in applications requiring lowoutput-voltage, high-current, and high entire-load-range efficiency such as computing devices and processors [1]–[8]. The contribution of this paper is to propose a comprehensive analysis and design guideline for multiphase buck converter with CMCOT control and current-balance loop. One is the compensated output voltage Vc, and the other is the summation current feedback signal isum·Ri, where Ri is the current sensing gain These two signals determine the turn-on timing of two duty cycles through PWM comparator and distributor. Current-balance control is achieved by sensing per-phase inductor current and adjusting per-phase on-time. The voltage-second balance method is used to derive the relationship between inductor current, the duty cycle D, and parasitic resistances in CCM [9]. If duty cycle is derived, it can be substituted into (4) to obtain inductor current
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