SiC vs GaN Head-to-Head Performance Comparison

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A lot of engineers don’t have a good feel for how gallium-nitride FETs perform compared to silicon-carbide equivalents. So GaN Systems devised two 650-V, 15-A switching supplies using SiC and GaN to see how they compared. In an interview conducted by WTWH Media’s Lee Teschler, Jim Witham explains the differences that emerged in this head-to-head study.

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Global Leaders Collaborate on GaN Technology

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OTTAWA, Ontario – October 2, 2017 – The world is challenged with unsustainable increases in power consumption, combating climate change, implementing cleantech technologies and meeting green, CO2 reduction initiatives. Taiwanese electronics manufacturers work at the forefront of these efforts. To meet these challenges, GaN Systems, the world’s leading provider of gallium nitride (GaN) power transistors, and Taiwan’s Ministry of Economic Affairs (MOEA) have entered into a Letter of Intent to collaborate on expanding the economic and technical benefits of GaN technology to Taiwan’s electronics companies. To further advance Taiwan’s leadership role in the electronics industry, recognizing the importance and benefits of GaN, the MOEA will provide assistance to GaN Systems to extend its in-country business and representation. This agreement brings together two powerful forces – the leading manufacturer of GaN transistors and the government body that oversees Taiwan’s electronics industry. Working together, this alliance will collaborate to help solve some of the world’s most daunting power challenges.

Ms. Mei-Hua Wang, Vice Minister of Taiwan’s Ministry of Economic Affairs (MOEA), commented on the development, “As Taiwan plays a preeminent role in the Asian electronics industry, we are pleased to provide GaN Systems with the resources to continue their success with our leading manufacturers. This Letter of Intent strengthens the bonds between GaN Systems and Taiwan’s electronics industry.”

GaN Systems’ CEO, Jim Witham, added, “GaN Systems is delighted to join forces with Taiwan’s MOEA. We see this as an important demonstration of how companies and government work together to reinforce partnerships amongst industry leaders and across industry segments.”

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Gallium Nitride Sets Innovation Bars Higher

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The following article, written by Mathew Dirjish, originally appeared in Sensors Online.

Silicon has been the mainstay of semiconductor fabrication for as long as one can remember. It is the meat of transistors, OP amps, microprocessors, MCUs, PLCs, and numerous other devices. The material has proven more than viable and reliable and will be with us for countless years ahead.

Starting with power devices, a not so new kid on the block is proving to be silicon’s competitor to be reckoned with. Gallium nitride (GaN) is a semiconductor commonly used in light-emitting diodes. It is a hard material with a crystal structure, a property that makes it desirable for use in opto applications and high-power devices.

To make a long technical story shorter, the material has proven itself in fabricating power devices. Certain sources indicate that the first enhancement-mode gallium nitride transistors became available in 2010.

Designed to replace power MOSFETs in applications where switching speed or power conversion efficiency is critical, the GaN transistors exhibit significant advantages over silicon MOSFETs, particularly in the cost versus performance challenges.

Now, it appears GaN is making inroads to the world of sensors. It stands to reason since many sensors are silicon based and with the emerging need for multiple sensors on a chip, a.k.a., sensor fusion, GaN could open up many new areas for sensor innovation. The possibility of combining power functions, sensors, and optical functions on a small device may not be too far away in the future.

To get the best insight into this material and what we can see in the future, I had a brief Q&A with Jim Witham, the CEO of GaN Systems. The company manufactures a range of gallium nitride high power transistors for consumer, enterprise, industrial, solar/wind/smart-grid, and transportation power-conversion applications. The devices boast exceptionally low on-resistance, negligible charge storage, and enable switching efficiencies in excess of current silicon devices.

Mat Dirjish (MD): GaN Systems focuses on the use of gallium nitride instead of silicon in the development of power semiconductors. For some of our readers who may not be aware of the benefits of GaN and the tradeoffs of silicon, what sets the use of GaN above silicon for power applications?

Jim Witham (JW): By replacing legacy components with GaN transistors, engineers can design electronic systems that are 4x smaller, 4x lighter, that exhibit 4x less energy loss, and are less costly. The performance advantages provide customers with a profound array of benefits across markets from the IoT and datacenter servers to industrial equipment, electric vehicles (EVs), and autonomous vehicles.

MD: Although the primary focus appears to be transistors, HEMTs in particular, GaN-based violet laser diodes are used in Blu-Ray disc players. Do you foresee GaN being viable for other semiconductor types and if so, what is possible?

JW: The three major applications for GaN are LED, power, and RF. GaN Systems focuses on power. The fourth application showing great potential is GaN sensors.

MD: Is GaN easily substituted for silicon in general semiconductor design/manufacturing? What are the major challenges in making the switch?

JW: In general, yes, one can think of our GaN transistors as just extremely fast MOSFETs. Second, we have solved the design challenges for customers by making our transistors easy to use and providing the design tools engineers expect. Evaluation kits, discrete parts and reference designs are easily acquired through common sales channels. Datasheets, application notes, and solution design files are available with an easy click from our website.

MD: Several sensor types are implemented on silicon and sensor fusion, the combination of two or more sensor types on a single chip, relies on silicon. Is GaN a viable material for creating low-power, fast reacting sensors and multiple sensor integrations?

JW: GaN sensors are receiving a lot of attention and focus today. Mercury detection, pH analysis, hydrogen sensing, and DNA and protein sensing are just a few of the areas being researched with GaN HEMT materials. As mentioned above, this could emerge as the fourth, very large application for GaN.

MD: In July, BMW’s investment arm, BMW i Ventures, made a significant investment in GaN Systems, which is viewed as a major display of confidence in the technology. What are some of the projects GaN will be working on as a result of this investment?

JW: As we recently announced, GaN Systems will use the funds to expand our global sales efforts and to accelerate new product development. The products under development will be used to help engineers design more efficient electronic systems in the markets we target, which include consumer, datacenter, industrial and transportation applications.

MD: What types of emerging applications are offering growth potential for GaN devices? Obviously there will be greater demands for power devices in IoT and IIoT systems. What impact will areas such as energy harvesting, artificial intelligence, augmented reality, and virtual reality on the direction of GaN devices?

JW: The IoT and IIoT segments, and I would add 5G to those, are very exciting. These applications generate massive amounts of data, driving the need for increased data storage and processing, which requires more power supplies and servers. GaN devices reduce power consumption and increase power supply density, saving customers operating costs and allowing more servers in the same rack. The same holds true for the automotive ADAS and autonomously driven vehicle space where automotive manufacturers are building datacenters to manage the 10X explosion in data generated by these vehicles. EV and HEV systems are undergoing extensive electrification, which increases semiconductor demand 3x to 4x more than vehicles currently require.

Wireless power transfer is an emerging application with a direct tie to sensors. This is a perfect method to supply power to these sensing devices. Then there are robot and drone applications that are just starting to take off; these will also leverage the advantages of wireless power transfer and charging.

Another emerging application for GaN is artificial intelligence and machine learning. These applications use microprocessors, GPUs and memory in their high-performance computing (HPC) that require higher power, in the order of 500 W in the same volume that currently delivers only 200 W. GaN transistors provide a path for designers to increase power density without adding volume or weight.

MD: If you can speak about it, what developments does GaN Systems have on the drawing board for the future?

JW: Our plans include product expansion in several different vectors – voltage, current, and frequency performance. Additionally, we will integrate features to save customers more space, cost and time.

In summary, GaN is undoubtedly going to make more than a little noise in several markets, particularly the sensors markets while continuing to make great strides in the power sector. It is definitely a technology to keep a steady eye on.

Ottawa tech firm GaN Systems revved up about BMW investment

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This article, written by David Sali, was originally published in the Aug. 25th issue of the Ottawa Business Journal.

Kanata company’s next-generation semiconductor technology attracts multimillion-dollar injection of equity led by German automaker

A Kanata firm that makes transistors that help electric and autonomous vehicles run more efficiently has landed millions in funding from one of the world’s leading automakers.

GaN Systems recently announced the new infusion of capital led by BMW i Ventures, the investment arm of the German high-performance car manufacturer. Existing investors BDC Capital, Chrysalix Venture Capital, Cycle Capital Management, RockPort Capital and Tsing Capital also contributed to the round.

Company officials would not divulge the size of the latest investment, but several media outlets have valued it at more than C$40 million.

It’s the latest funding win for GaN Systems, a rapidly growing west-end firm that specializes in high-speed semiconductors made of gallium nitride. GaN, as it’s commonly known, is a byproduct of aluminum and zinc production known for its incredibly high heat capacity and conductivity.

Read more.

Newly Enhanced LTSpice Model Simplifies Designing with GaN

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Engineers gain a head-start and design accuracy

OTTAWA, Ontario, August 15, 2017 – Power system design engineers want to be fast, accurate and confident with their simulated designs prior to building hardware. Achieving these goals with GaN designs has become easier with GaN Systems’ new set of LTSpice models. Increasing efficiency and power density requires proper layout and understanding of the characteristics of these fast transistors. GaN Systems provides a full-featured set of LTSpice simulation files that are available now for download that allow for a variety of inputs and simulations options; select the product of interest and then select the LTSpice button. Additionally, LTSpice application notes GN007 and GN008 are available on the GaN Systems website.

The LTSpice model user guide helps engineers model systems at three levels, ranging from an initial overview of circuit performance to detailed analysis and fine tuning of the design:

  • Level 1: Basic adjustment and analysis of switching speeds, optimized for quick simulation.
  • Level 2: In addition to Level 1 features, includes thermal inputs and Cauer thermal RC network transient models for simulating the device junction temperature and self-heating effect.
  • Level 3: In addition to Level 2 features, includes parasitic losses, provides the most accurate model with longest simulation times.

To confirm the accuracy of the LTSpice model, laboratory measurements of GaN E-HEMT switching losses were recorded using a half-bridge, double-pulse test circuit. The switching losses measured in the test were then compared with the LTSpice model simulations. The comparison demonstrates a strong correlation between the simulated results and real-time circuit measurements. With a 400 V, 0 to 30 A switching current setup using a 650 V, 50 milliohm GS65008T device, the difference between actual measurement and the simulated model is less than 5%, a very good number for Eon/Eoff accuracy. The outcome is a simulation tool that provides a convenient and accurate way to understand GaN switching characteristics, evaluate GaN switching performance under different electrical conditions and build overall confidence in a new product design.

Larry Spaziani, GaN Systems VP of Sales and Marketing, commented on the benefits of the LTSpice tool, “By developing and making available for download this full-featured LTSpice simulation tool, GaN Systems has made it easier for power system designers to leverage all the benefits of GaN transistors and to optimize their system performance. Rarely do designers use spice simulation to estimate Eon/Eoff; with our models they can. We expect that this tool will help designers more fully understand GaN technology and accelerate their design completion.”

BMW i Ventures Leads Strategic Investment in GaN Systems

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Mountain View – July 18, 2017 – GaN Systems, the world’s leading provider of GaN power transistors, announced the closing of an investment round led by BMW’s investment arm, BMW i Ventures. Consistent with its investment strategy, BMW i Ventures recognizes that GaN Systems’ products maximize the efficiency of electronic systems while dramatically reducing size, weight and overall system cost. The investment will be used to expand global sales and accelerate new product development. BMW i Ventures joins the existing investors: BDC Capital, Chrysalix Venture Capital, Cycle Capital Management, RockPort Capital and Tsing Capital.

“GaN Systems’ power transistors have created new possibilities for engineers to build the power electronics demanded by today’s systems. Gallium Nitride-based transistors have become, in my opinion, the next big stepping stone in miniaturization. We have seen systems ¼ of the size while providing better efficiency than traditional silicon-based alternatives. With GaN, any system that needs power can become smaller, lighter and more efficient. These capabilities are particularly relevant in the automotive sector,” stated Uwe Higgen, managing director, BMW i Ventures.

GaN Systems’ CEO, Jim Witham, commented on the landmark investment, “From computer/phone chargers and data center servers to factory motors and electric cars, our customers have validated the GaN value proposition of small, efficient, low-cost power electronics. These benefits are widely recognized by the world’s biggest companies across all industries.”

“There are many examples of how GaN benefits power systems,” continued Higgen. “With autonomous cars, there will be the need to massively scale the data center infrastructure. Data center power consumption is one of the biggest cost drivers, and increasing the efficiency of power conversion will account for billions of dollars in cost savings and enable a more sustainable infrastructure around the globe.”

A Performance Comparison of GaN E-HEMTs versus SiC MOSFETs in Power Switching Applications

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This article was originally published in the June 2017 issue of Bodo’s Power Systems.

Research on wide bandgap (WBG) devices has been conducted for many years. The reason that the properties of Gallium Nitride (GaN) and Silicon Carbide (SiC) excite power engineers is because they show substantial performance improvements over their silicon-based counterparts.

By Jason (Jianchun) Xu and Di Chen, GaN Systems Inc.

Research on wide bandgap (WBG) devices has been conducted for many years. The reason that the properties of Gallium Nitride (GaN) and Silicon Carbide (SiC) excite power engineers is because they show substantial performance improvements over their silicon-based counterparts. Both GaN and SiC have material properties superior to Si for switching power devices. WBG devices offer five key characteristics, including high dielectric strength, high-speed switching, tolerance of high operating temperature environments, high current density, and low on-resistance. However, currently, there are few papers that compare how GaN and SiC devices perform in real power switching applications. In this article, we present the results of a head-to-head comparison of GaN E-HEMTs and SiC MOSFETs used in a DC-DC synchronous buck converter application. Due to lower internal capacitances and zero reverse recovery charge, we conclusively demonstrate that GaN E-HEMTs offer significant improvements in power conversion efficiency, especially at higher frequencies.

For this study, the performance of the GaN transistor GS66508T (650 V/ 30 A, 50 mΩ) from GaN Systems Inc. was compared with the SiC MOSFET C3M0065090J (900 V/ 35 A, 65 mΩ) from CREE Inc. To simplify comparing the GaN E-HEMT and SiC MOSFET, the test used a common evaluation motherboard GS665MB-EVB, paired with an interchangeable daughterboard (Figures 1-4). These boards are configurable either as a buck, boost or double-pulse tester. The two daughterboards also have a very similar design. They both contain the same PCB layout, 2 oz. copper, 4 PCB layers, homogeneous thermal via and layout parasitics. The very fast switching speeds exhibited by GaN and SiC transistors require gate drivers that combine very high timing accuracy with excellent common-mode transient immunity (CMTI). To accommodate these criteria, Silicon Labs’ Si8271 isolated gate driver with high CMTI was used on both daughterboards.

Figure 1: GS66508T-EVBDB

Figure 2: C3M0065090J-EVBDB

Figure 3: Bottom-side of GS66508T-EVBDB

Figure 4: GS665MB-EVB

Table 1 shows the electrical characteristics of the GaN E-HEMT GS66508T and the Cree SiC MOSFET C3M0065090J. These characteristics have a major influence on the fundamental performance of the devices.

Table 1: Electrical Characteristics

A half-bridge, hard switching, double pulse test was conducted under 400 V/ 15 A on both GaN and SiC daughterboards. The turn-on resistor Rg(on) was 10 Ω, while the turn-off resistor Rg(off) was 1 Ω. The results of two double pulse switching tests follow. Figure 5 and Figure 6 show a close-up view of the turn-on and turn-off periods, and demonstrate the switching performance of the GaN E-HEMT GS66508T versus the SiC MOSFET C3M0065090. In the turn-on period, dv/dt of the GaN E-HEMT reached 90 V/ns, 4X faster than the SiC MOSFET 18 V/ns. In the turn-off period, dv/dt of the GaN E-HEMT performed 2X faster than the SiC MOSFET.

Figure 5: Double Pulse Test Hard Switch Turn-on

Figure 6: Double Pulse Test Hard Switch Turn-off

Fig. 7 shows the switching loss measurements with a drain-to-source voltage of 400 V, drain current from 0 to 30 A for GS66508T and C3M0065090J. The turn-on loss dominated the overall hard switching loss. For GaN E-HEMT, Eon at 0 A is the Qoss, caused by the Coss at the high side switch. For the SiC MOSFET, Eon at 0 A is the sum of Qoss and the reverse recovery charge Qrr at the high side switch. Using the same test conditions, the GaN E-HEMT shows a much improved Eon/Eoff. The Eon/Eoff difference between GaN and SiC can be quantified by calculating the switching loss: (Eon+Eoff)×fsw. For example, at 400 V/ 15 A, and 100 kHz, the switching loss Psw of GaN is 5.217 W, while the Psw of SiC is 15.211 W, ∆Psw=9.994 W. However, at 200 kHz, the Psw of GaN is 10.434W, versus a SiC Psw of 30.422 W, ∆Psw=19.988 W. The result, shown in Fig. 8, clearly shows that at higher switching frequencies, GaN provides a significant performance improvement over SiC. For instance, at 100 kHz, GaN provides 10 W savings, but in the same system at 200 kHz, 20W is saved.

Figure 7: Switching Energy of the GS66508T versus the C3M0065090J

Figure 8: 400 V/ 15 A GS66508T and C3M0065090J Switching Loss Comparison

To measure the thermal resistance R_(th(JA)) of both devices, a 35×35 mm heatsink was mounted on bottom of both daughterboards. In addition, an electrical fan with an air flow of 12.0 CFM (0.340 m3/min) was attached to the heatsink. Using the same test conditions, R_(th(JA)) for the C3M0065090J measured 7.724⁰C / W, versus an R_(th(JA)) for the GS66508T of 5⁰C / W. The thermal resistance from junction to ambient of GaN measured 1.5X better than SiC, as shown in Figures 9-11.

Figure 9: Thermal Resistance Comparison of GaN vs. SiC

Figure 10: GS66508T Thermal Resistance Setup

Figure 11: C3M0065090J Thermal Resistance Setup

A synchronous buck converter with an input voltage of 400 V and an output voltage of 200 V was tested. At a 200 kHz switching frequency, the output power varied from 100 W to 1 kW. Figure 12 compares the sync buck converter system efficiencies and the device’s hard-switching junction temperature using GaN E-HEMTs versus SiC MOSFETs. The graph shows that the efficiency and junction temperature using GaN E-HEMTs performed better than SiC MOSFETs under same test conditions. Power loss of the devices was equal to (Tj-Tamb)/(Rth(JA)). From 0 to 1 kW, at 200 kHz GaN Ploss is only 45%-59% that of SiC. Table 2 shows the performance improvement of GaN E-HEMTs over SiC MOSFETs at an output power of 900 W. At Pout = 900 W, the Tj of the GaN E-HEMT was 59⁰C lower than the SiC MOSFET, and the power loss of GaN was 5.38 W lower than that of SiC. The superior performance of GaN versus SiC can be attributed to its lower Eon/Eoff. Because the conduction loss was small, the switching loss (Eon+Eoff)*fsw accounts for over 85% of device’s total power loss. Hence, as the switching frequency increases, GaN E-HEMTs will perform better than SiC MOSFETs.

Figure 12: Synchronous Buck DC/DC System Efficiency (400 V – 200 V, 200 kHz, Tamb = 25°C)

Table 2: Power Loss and Junction Temperature Comparison at Pout = 900 W

Conclusion

This article compares the fast switching device characteristics of GaN E-HEMTs versus the best competing SiC MOSFETs. When used in synchronous buck DC/DC converter applications, the converters that use GaN E-HEMTs exhibit much higher efficiencies than ones that use SiC MOSFETs. In this application, the results clearly demonstrate that the performance of GaN E-HEMTs exceeds the performance of the best SiC MOSFETs in terms of switching speed, parasitic capacitance, switching loss and thermal characteristics. Furthermore, compared with their SiC counterparts, GaN E-HEMTs facilitate the construction of significantly more compact and efficient power converter designs.

Customer Products on Display at PCIM 2017

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This video, originally published on Electronics Products Magazine’s YouTube channel, was recorded at PCIM 2017. GaN Systems’ CEO, Jim Witham, talks with Alix Paultre about the adoption of GaN technology and describes some of the 30+ customer products displayed at PCIM that are performance-optimized by GaN transistors.

Watch on YouTube >

Paralleled GaN Transistors Boost Converter Power Up to 100kW

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This article was written by Sam Davis and first appeared in powerelectronics.com
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Paralleling GaN transistors increases the power handling capability of a high-efficiency and high-power density converter. To be successful, parallel operation depends on the designer’s ability to deal with parasitic elements within the GaN devices as well as those associated with interfacing circuits.

Characteristics of enhancement-mode (e-mode) GaN, such as positive temperature coefficient of RDS(ON) and a temperature-independent threshold voltage, make them excellent candidates for paralleling. GaN Systems’ GS66516T is a GaN transistor that has these characteristics so it can operate efficiently and reliably in a parallel configuration; its features are listed below. After analyzing its parasitics, paralleled GS66516T transistors will be designed into the prototype of a half-bridge capable of 240A rated current.

In parallel applications, the junction temperature of low RDS(ON) GaN transistors increase to balance current sharing during the ON state, because of positive temperature coefficiency of RDS(ON). On the other hand, the threshold voltage (Vth) of GaN Systems’ GS66516T is nearly constant as a function of junction temperature, as shown in Fig. 1. A device with lower Vth turns on earlier and turns off earlier, resulting in a higher turn-on switching loss and a lower turn-off switching loss. However, because of the characteristics of GaN, dynamic current sharing and switching loss distribution is not affected by unbalanced temperature distribution of paralleled transistors.

GaN Systems GS66516T features:

– 650 V enhancement mode GaN power switch
– Top-side cooled configuration
– RDS(ON) = 25 mOhms
– IDS(max) = 60 A
– Ultra-low FOM (Figure of Merit = RDS(ON) × QG ) Island Technology® die
– Low-inductance GaNPX® package
– Gate drive requirements (0 V to 6 V)
– Transient tolerant gate drive (-20/+10 V )
– Switching frequency >10 MHz
– Fast and controllable fall and rise times
– Reverse current capability
– Zero reverse recovery loss
– 9 x 7.6 mm2 PCB footprint
– Dual gate and source sense pads for optimal board layout
– RoHS 6 compliant


1. Vth of GS66516T vs. Temperature.

Parasitics are the main challenge for configuring parallel operation of the power stage and gate driver circuits, which are sensitive to the high di/dt and dv/dt during the switching process. We need to remove bottlenecks of applying GaN to ~100 kW power electronics systems, which are not only limited to ZVS typologies but also hard switching applications.

Parasitic Inductance

Figure 2 shows the equivalent circuit of a half- bridge power stage consisting of two high-side and two low-side GaN in parallel. This includes all the parasitic inductance in the gate drive loop and power commutation loop. It is necessary to understand the effects of parasitics and device characteristics on paralleled transistors when switching on.


2. Equivalent Circuit of Half Bridge with 2x GaN HEMTs in Parallel.

When the controller signal is added to the low-side gate driver, the higher switch of the totem pole circuit in the gate driver chip turns on. The gate driver capacitor begins to charge the CISS (CGS + CGD) of the paralleled GaN. When VGS>Vth (threshold voltage of GaN), the two-Dimensional Electron Gas (2DEG) begins conducting, as shown in Fig. 3. To simplify the analysis, we can divide the switching on process of paralleled GaNs into four periods: P1-delay period, P2-di/dt period, P3-dv/dt period, P4-remaining switching period.


3. State of GaN transistor when switching on.

Table 2 presents the effects and design rules of various parasitics in the gate drive loop and power loop. These parameters refer to the equivalent circuit in Fig. 2 of a half-bridge employing parallel GaN transistors.

Parasitic inductance is a function of the magnetic flux caused by the current. According to the law of electromagnetic induction, with the multi-layer magnetic-flux-canceling design strategy, the parasitics of the trace could be greatly reduced. The direction of the commutation current on two adjacent layers are opposite so that the generated flux outside the loop cancel each other.

Compared to Direct Bonded Copper (DBC) substrate, the PCB could easily adopt the multi-layer structure and smaller distance between layers to obtain a better magnetic flux canceling effect.


4. 240A/650V half-bridge employs four paralleled GS66516T GaN transistors.

Figure 4 is the schematic of the half-bridge power stage consisting of four high-side and four low-side GaN transistors in parallel rated at 240A/650V. Figure 5 depicts the board layout of the half-bridge.


5. Layout of 240A/650V GaN transistors based Half Bridge.

GaN Systems’ GaNPX packaging technology eliminates leads and bonding wires, which also aids circuit performance. Compared with using traditional TO-247 packages, this approach reduces stray inductance by >90% (Fig. 6).

The half bridge with four GaN transistors in parallel was modeled in Ansys Q3D. The power loop and gate-driver loop inductance were evaluated by Finite Element Analysis. The commutation loop inductance of the proposed design is only 0.7 nH, about one-fourth of the best available E-mode GaN-based power module. For each paralleled GaN transistor, quasi-common source inductance is <0.2 nH, and gate drive loop inductance is 4.2 nH.

6. GaNPX packaging technology.

Parasitic Capacitance

Parasitic capacitance is another design consideration. During the switch-on process, COSS as well as the reverse recovery charge (as seen in Si/SiC MOSFETs) increases the current spike and switching loss. Generally speaking, in hard switching application, the more transistors we parallel, the higher switching loss we get. There are an optimum number of paralleled GaN transistors to reach the highest efficiency for a specific application.

In Zero Voltage Switching (ZVS) application, during the dead time, the reactive energy stored on magnetic components begins to discharge and charge the parasitic capacitance. To secure ZVS, the reactive power has to be higher than the stored energy in the parasitic capacitance of GaN transistors and PCB board and the dead time loss of GaN transistors. On the other hand, to increase the efficiency of system, the reactive power needs to be controlled as close to the required energy as possible, which requires a precise modeling of parasitic capacitance. Parasitic capacitance of PCB and magnetic components can’t be ignored when compared with the ultra-small COSS of a GaN transistor. The PCB parasitic capacitance is modeled in Ansys Q3D in Figure 7.


7. Parasitic Capacitance Extraction in Q3D.

The current spike measured during the hard switching-on in the lower switches is contributed by the displacement charge current of the parasitic capacitance between voltage jumping point and BUS+ node, which was measured in Fig. 8. The measured equivalent capacitance is about 2 nF.

Total parasitic capacitance of the half-bridge power stage is 3.2 nF (1.73 nF to BUS+ node, 1.48 nF to BUS- node).


8. COSS Charge @ Different Load Current.

Experimental Verification

Figure 9 shows the prototype of a half-bridge power stage consisting of four high-side and four low-side GaN transistors in parallel that is rated at 240 A / 650 V. It has been experimentally verified by the double pulse test.


9. Prototype of 240A/650V GaN-based Half Bridge.

As shown in double pulse test waveform in Fig. 10, reliable hard switching on and off are realized at the rated power, 240 A/400 V with clean transition waveforms, while the spike on VDS during switching off is only 52 V even with close to 60 V/ns turn-off speed, which shows the benefit of low power loop inductance.


10. Double Pulse Test Waveform @240 A/400 V.

GaN parameters

– HEMT = High Electron Mobility Transistor
– RDS(ON) = On-state drain-to-source resistance
– CGS = Gate-to-source capacitance
– CGD = Gate-to-drain capacitance
– CISS = Input capacitance
– COSS = Output capacitance
– CRSS = Reverse transfer capacitance
– QG = Total gate charge
– VGS = Gate-to-source voltage
– VDS = Drain-to-source voltage
– IDS(max) = Maximum drain-source current

PFC Design – Maximizing Efficiency and Lowering Cost with GaN Transistors

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GaN Systems releases industry’s first E-HEMT bridgeless-totem-pole Power Factor Correction reference design

OTTAWA, Ontario, May 9, 2017 – Achieving efficiencies greater than 98% in conventional Power Factor Correction (PFC) circuits is challenging. The major hurdle is fixed diode bridge losses. An option to overcome this is to use silicon MOSFETs in place of the diodes to achieve efficiencies of 99% or more. However, this BTPPFC approach suffers from poor reverse recovery performance, is suitable only for low power, and requires complicated control parameters. GaN Systems mitigates these drawbacks by replacing silicon MOSFETs with GaN E-HEMTs that eliminate the body diode (zero Qrr) and exhibit very fast switching. To provide design engineers with a platform to demonstrate the performance of GaN HEMTs, GaN Systems has released the GS665BTP-REF, the industry’s first 3 kW continuous current mode (CCM) E-HEMT-based BTPPFC reference design.

The 3 kW GS665BTP-REF reference design compares the switch-on losses of a silicon-based CoolMOS CFD2 with losses exhibited by a GaN Systems 650 V E-HEMT. The results show that GaN has superior reverse recovery. Operating the CCM BTPPFC at 50 kHz, GaN dissipates only 0.75 W switching loss due to the Qoss Loss at turn-on, while the CoolMOS CFD2 shows a loss of 20 W, solely due to Qrr. The result is excellent hard-switching performance in a CCM BTPPFC with maximized efficiency.

Comprehensive documentation for the GS665BTP-REF reference design, entitled “High-Efficiency CCM Bridgeless Totem Pole PFC Design using GaN E-HEMT,” is available for download from GaN Systems website. The documentation includes the motivation, operating principles, and design considerations for the BTPPFC using 650 V GaN E-HEMTs. Also included in the documentation are discussions pertaining to test setup, test results (i.e. efficiency, power factor, waveforms, thermal measurements), and applications.

Paul Wiener, GaN Systems VP of Strategic Marketing, commented on the release of the reference design, “Now power design engineers have a tool to help them leverage the increased efficiencies and reductions of space, weight and BOM costs provided by GaN transistors. Today we are seeing these benefits show up in products as diverse as battery chargers, energy storage systems and power supplies in enterprise applications. As design engineers explore ways to improve power system performance, we expect that this reference design will play an instrumental role in the development of many more commercial products.”