iCoupler技术为AC/DC设计中的氮化镓(GaN)晶体管带来诸多优势

winniewei 提交于 周一, 09/28/2020
iCoupler技术为ACDC设计中的氮化镓(GaN)晶体管带来诸多优势

作者:ADI现场应用工程师Robbins Ren

Highly efficient ac/dc power supplies are key to the evolution of the telecom and datacom infrastructure, as power consumption grows rapidly due to hyperscale data centers, enterprise servers, or telecom switching stations. However, the power electronics industry has reached the theoretical limit of silicon MOSFETs. Meanwhile, recent gallium nitride

top:-.5pt;mso-text-raise:.5pt">(GaN) transistors have emerged as a high performance switch to replace silicon-based MOSFETs, offering increased energy conversion efficiency and enabling greater density. A new isolation concept with new specifications is required to address the advantages of the GaN transistors.

大规模数据中心、企业服务器或电信交换站使得功耗快速增长,因此高效AC/DC电源对于电信和数据通信基础设施的发展至关重要。但是,电力电子行业中的硅MOSFET已达到其理论极限。同时,近来氮化镓(GaN)晶体管已成为能够取代硅基MOSFET的高性能开关,从而可提高能源转换效率和密度。为了发挥GaN晶体管的优势,需要一种具有新规格要求的新隔离方案。

GaN transistors can switch much faster than silicon MOSFETs and can achieve lower switching losses due to:

GaN晶体管的开关速度比硅MOSFET要快得多,并可降低开关损耗,原因在于:

u  栅极电容和输出电容更低。

u  较低的漏源极导通电阻(RDS(ON))可实现更高的电流操作,从而降低了传导损耗。

u  无需体二极管,因此反向恢复电荷(QRR)低或为零。

GaN transistors can enable most ac/dc power supplies that consist of separate power factor correction (PFC) and dc-to-dc sections: a front-end, bridgeless PFC and the following LLC resonant converter (two inductors and one capacitor). This topology exclusively relies on half-bridge and full-bridge circuits as shown in Figure 1.

GaN晶体管支持大多数包含单独功率因数校正(PFC)和DC-DC部分的AC/DC电源:前端、无电桥PFC以及其后的LLC谐振转换器(两个电感和一个电容)。此拓扑完全依赖于图1所示的半桥和全桥电路。

With a digital signal processor (DSP) as the main controller along with the GaN transistor used to replace the silicon MOSFETs, a new isolation technology is required to address the higher switching frequencies. This mainly includes the isolated GaN drivers.

如果将数字信号处理器(DSP)作为主控制器,并用GaN晶体管替换硅MOSFET,就需要一种新的隔离技术来处理更高的开关频率。这主要包括隔离式GaN驱动器。

图1.适合电信和服务器应用的典型AC/DC电源

Figure 1. Typical ac/dc power supply for telecom and server applications.

图1.适合电信和服务器应用的典型AC/DC电源

Typical Isolation Solutions and Requirements典型隔离解决方案和要求

UART Communication Isolation

UART通信隔离

The change from a previous analog controlled system to a DSP controlled system requires the isolation of the pulse-width modulated (PWM) signals and the additional control signals. The dual-channel ADuM121 can be used for UART communication between DSPs. To minimize the total system size required for the isolation, the epoxyresinsealantisusedinboardassembly.Smallersizeandhighpowerdensity arecriticalintheevolutionofac/dc.Smallerpackageisolatorsarerequired.

从以前的模拟控制系统转变为DSP控制系统时,需要将脉宽调制(PWM)信号与其他控制信号隔离开来。双通道ADuM121可用于DSP之间的UART通信。为了尽量减小隔离所需系统的总体尺寸,进行电路板组装时使用了环氧树脂密封胶。小尺寸和高功率密度在AC/DC电源的发展过程中至关重要。市场需要小封装隔离器产品。

PFC Section Isolation

PFC部分隔离

The propagation delay/skew, negative bias/clamp, and size of the ISO gatedriver iscriticalforGaNincontrasttoMOS.Todriveahalf-bridgeorfull-bridgetransistor with GaN, the ADuM3123 single-channel driver can be used for the PFC section and the ADuM4223dual-channel driver for the LLCsection.

与使用MOS相比,使用GaN时,传输延迟/偏斜、负偏压/箝位和ISO栅极驱动器尺寸非常重要。为了使用GaN驱动半桥或全桥晶体管,PFC部分可使用单通道驱动器ADuM3123,LLC部分则使用双通道驱动器ADuM4223

Powering the Devices Behind the Isolation Barrier

为隔离栅后的器件供电

BasedonADI’sisoPower®technology,whichisdesignedforpowertransferacross the isolation barrier, the ADuM5020 is a compact chip solution that can match a GaNtransistor’sauxiliarypowersupplywiththatofagate.

ADI公司的isoPower®技术专为跨越隔离栅传输功率而设计,ADuM5020紧凑型芯片解决方案采用该技术,能够使GaN晶体管的辅助电源与栅极的辅助电源相匹配。

Isolation Requirements

隔离要求

To take full advantage of a GaN transistor, the preferred requirements for isolated gate drivers are:

为了充分利用GaN晶体管,要求隔离栅极驱动器最好具有以下特性:

u  最大允许栅电压<7 V

u  开关节点下dv/dt>100 kV/ms ,CMTI为100 kV/µs至200 kV/µs

u  对于650 V应用,高低开关延迟匹配≤50 ns

u  Negative voltage clamp (–3 V) for turning off用于关断的负电压箝位(–3 V)

There are several solutions to drive both the high-side and low-side of the half-bridge transistor. One myth about the traditional, level-shifted, high voltage driveris that the simplest single-chip implementation is widely used only for silicon-basedMOSFETs.Insomehighendproducts(forexample,powersupplyforservers), the ADuM4223 dual-isolated driver is used to drive an MOS for compact designs. However, when turning to GaN, the level-shift solution has disadvantages, such as very large propagation delay and limited common-mode transient immunity (CMTI) and is not optimal for high switching frequency. The dual-isolated driver lacks layout flexibility in comparison to single-channel drivers. Meanwhile, it has difficultyintheconfigurationofthenegativebias.Table1showsacomparisonof thesemethods.

有几种解决方案可同时驱动半桥晶体管的高端和低端。关于传统的电平转换高压驱动器有一个传说,就是最简单的单芯片方案仅广泛用于硅基MOSFET。在一些高端产品(例如,服务器电源)中,使用ADuM4223双通道隔离驱动器来驱动MOS,以实现紧凑型设计。但是采用GaN时,电平转换解决方案存在一些缺点,如传输延迟很大,共模瞬变抗扰度(CMTI)有限,用于高开关频率的效果也不是很理想。与单通道驱动器相比,双通道隔离驱动器缺少布局灵活性。同时,也很难配置负偏压。表1对这些方法做了比较。

Table 1. Comparison of Different Methods in Driving a GaN Half-Bridge Transistor

表1.驱动GaN半桥晶体管不同方法的比较

Solution

解决方案

Technology

技术

Merits

优点

Challenge

挑战

ADI product

ADI产品

Integrated high-side and low-side driver

集成高端和低端驱动器

Level shift

电平转换

Simplest single-chip solution

最简单的单芯片解决方案

Large delay time, limited CMTI,
external bootstrap circuit

大延迟时间、有限的CMTI、
外部自举电路

 

Dual-isolated Integrated driver

双通道隔离集成驱动器

Magnetic

磁性

Single-chip solution

单芯片解决方案

Sacrifice layout flexibility,
need time to charge
the bootstrap cap

牺牲布局灵活性、
需要时间给
自举电容充电

ADuM4223

ADuM4223

Single-channel isolated driver

单通道隔离驱动器

Magnetic

磁性

Easy for layout, high CMTI, low propagation delay/skew

易于布局、高CMTI、低传输延迟/偏斜

Require external auxiliary
power supply

需要外部辅助
电源

ADuM3123, ADuM4121

ADuM3123、ADuM4121

Isolators and ISO power

隔离器和isoPower

Magnetic

磁性

Layout flexibility, easy for negative bias, no bootstrap circuit

布局灵活、负偏压配置简单、无自举电路

High cost, EMI issue

成本高、EMI问题

ADuM110+ ADuM5020

ADuM110+ ADuM5020

图2.在isoPower器件中实现UART隔离和PFC部分隔离,需要采用ISO技术及其要求

Figure 2. Typical ISO opportunity and requirement showing the UART isolation and PFC section isolation in isoPower devices.图2.在isoPower器件中实现UART隔离和PFC部分隔离,需要采用ISO技术及其要求

Single-channel drivers are ready for GaN transistors. A typical single-channel driveristheADuM3123,usingexternalpowersuppliedbyZenerdiodesanddiscrete circuits for negative bias (optional) as shown in Figure3.

对于GaN晶体管,可使用单通道驱动器。ADuM3123是典型的单通道驱动器,可使用齐纳二极管和分立电路提供外部电源来提供负偏压(可选),如图3所示。

New Trend: Customized, Isolated GaN Modules

新趋势:定制的隔离式GaN模块

Presently, GaN devices are typically packaged separately from their driver. This is due to the differences in the manufacturing processes of GaN switches and isolation drivers. In the future, integrating the GaN transistors and the isolation

目前,GaN器件通常与驱动器分开封装。这是因为GaN开关和隔离驱动器的制造工艺不同。未来,将GaN晶体管和隔离

barrier drivers into the same package will further enhance the switching performance as it will reduce the inductor parasitics. Some key telecom vendors plan to package their GaN systems as individual customized modules themselves. Inthelongterm,thedriverforGaNsystemsmayenableitsimplementationintosmaller size isolator modules. Tiny, single-channel examples such as the ADuM110N (low propagation delay, high frequency) and the isoPower ADuM5020, which offer simplicity in design, as shown in Figure 4, to support thistrend.

栅驱动器集成到同一封装中将会减少寄生电感,从而进一步增强开关性能。一些主要的电信供应商计划自行封装GaN系统,构建单独的定制模块。从长远来看,用于GaN系统的驱动器也许能够集成到更小的隔离器模块中。如图4所示,ADuM110N等微型单通道驱动器(低传输延迟、高频率)和isoPower ADuM5020设计简单,可支持这一应用趋势。

图3.用于GaN晶体管的单通道、隔离式isoCoupler驱动器

Figure 3. A single-channel, isolated isoCoupler driver application overview for a GaN transistor.图3.用于GaN晶体管的单通道、隔离式isoCoupler驱动器

图4.iCoupler ADuM110N和isoPower ADuM5020非常适合Navitas GaN模块应用

图4.iCoupler ADuM110N和isoPower ADuM5020非常适合Navitas GaN模块应用

Conclusion

结论

GaN transistors with smaller device sizes, lower on resistance, and higher working frequency offer many advantages over traditional silicon-based MOSFETs. Adopting GaN technology could cut total solution size without compromising efficiency. GaN devices have great prospects, especially in medium and high voltage power supplies. ADI’s iCoupler® technology brings excellent benefits in driving the emerging GaN switches and transistors.

与传统硅基MOSFET相比,GaN晶体管具有更小的器件尺寸、更低的导通电阻和更高的工作频率等诸多优点。采用GaN技术可缩小解决方案的总体尺寸,且不影响效率。GaN器件具有广阔的应用前景,特别是在中高电压电源应用中。采用ADI公司的iCoupler®技术驱动新兴GaN开关和晶体管能够带来出色的效益。

References

参考资料

Bismuth,Alain.TheComingHardwareRevolutioninDataCenterEnergyEfficiency.” GaN Systems, Inc., April2020.

Bismuth、Alain。“针对数据中心能源效率即将到来的硬件革命”GaN Systems, Inc.20204月。

EiceDRIVER 1EDF5673K and 1EDS5663H.” Infineon Technologies AG, May 2018.

EiceDRIVER 1EDF5673K1EDS5663H。”Infineon Technologies AG,2018年5月。

GN001 Application Brief: How to Drive GaN Enhancement Mode HEMT.” GaN Systems, Inc., April 2016.

GN001应用简报:如何驱动GaN增强模式HEMT”GaN Systems, Inc.20164月。

Oliver, Stephen. “GaN Power ICs: Integration Drives Performance.” Bodo’s Power Conference, Munich. Navitas, December 2017.

OliverStephen。“GaN功率IC:通过集成提升性能。”慕尼黑Bodo功率会议。Navitas,2017年12月。

About the Author

作者简介

Robbins Ren is a field applications engineer located in Shenzhen, China. Robbins joined ADI in 2010 and is responsible for power and iCoupler product support for communications customers in China. He received his master’s degree in power electronics from South China University of Technology. He can be reached at robbins.ren@analog.com.

Robbins Ren是中国深圳的一名现场应用工程师。Robbins于2010年加入ADI公司,负责中国通信客户的电源和iCoupler产品支持。他获得了华南理工大学电力电子硕士学位。

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