在USB-C PD同步整流器中使用GaN hemt:方法和设计指南。
由于对高功率密度的持续需求，USB-C快速充电器的开关频率需要增加，以减小变压器和滤波器组件的尺寸。基于宽带隙(WBG)半导体材料的新兴技术为提高功率密度提供了新途径。在高开关频率下，用于同步整流器(SR)开关的GaN hemt具有较低的电荷和更快的开关过渡的优点。此外，在相同的额定电压和导通电阻下，GaN HEMT的尺寸比硅(Si) MOSFET的尺寸小。尽管有这些明显的优势，最先进的系统仍然使用MOSFET sr。但这背后的原因是什么?与mosfet相比，GaN相对较高的第三象限(体二极管)模式压降在开/关延迟时间内引入了更高的传导损失。这些“死区”损耗随着开关频率的增加而增加。为了使这些损失最小化，必须对控制器电路进行优化，以缩短开关门偏置的延迟。最先进的SR控制器具有数十到数百纳秒的延迟时间。这在LLC、有源箝位反激(ACF)，特别是准谐振(QR)反激等拓扑结构中引入了重大损失。 Even with a well-optimized controller, the delay times could be quite long, still in the order of tens of nanoseconds, due to PCB layout parasitics that affect the accuracy of drain-source voltage (VDS) sensing and reaction time of the SR controller. However, by addressing the issues during the design process, the full potential of GaN in SR applications can be realized. This paper presents the methodology of using GaN HEMTs for SR in USB-C PD charger and adapter designs. First, we provide an overview and comparison of the most common charger & adapter topologies used in the market. Then synchronous rectification characteristics are discussed, and design tips are provided regarding the usage of GaN HEMT as SR. Finally, we introduce Infineon’s 65 W Full Gan ACF converter Evaluation Board.
由博士Gökhan森，高级职员工程师，英飞凌技术
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