1 Introduction

A loss of power in data center server power-supply units can interrupt everything from entertainment to financial transactions to home security systems. Specifications such as the V2 Power Shelf Specification from the Open Compute Project (OCP) [1] emphasize the need to reduce server downtime with robust AC dropout control algorithms. In addition, the need for cost-effective solutions in data centers to improve power factor correction (PFC) light load and peak efficiency while shrinking passive components is becoming difficult with conventional continuous conduction mode control [2-8].

To address this problem, TI developed a gallium nitride (GaN)-based high-density design using two-phase integrated triangular current mode (iTCM) PFC (Figure 1) [9]. Low-value inductors operating at a high frequency have enabled the high efficiency (>99%) and power density (120 W/in³) of this design. These small inductors present a unique problem to AC dropout recovery in that only a few microseconds of switch on-time can result in over 70 A of switch current. In addition, any delays in timing can also result in significant reverse current, further exacerbating PFC recovery. Keeping the current levels at a safe magnitude and preventing reverse current required the development of a new solution to the AC dropout and recovery problem. This article discusses this solution with lab verification data based on the Variable-Frequency, ZVS, 5-kW, GaN-Based, Two-Phase Totem-Pole PFC Reference Design [10], for which Table 1 lists the primary components and system specifications.