GaN FETs Enable EVs & Industrial Power Designs

Article By : Maurizio Di Paolo Emilio

The company claims its next generation of 600-V and 650-V GaN FETs for automotive and other industrial applications achieve 99% efficiency.

Texas Instruments has announced its next generation of 600-V and 650-V gallium nitride (GaN) field-effect transistors (FETs) for automotive and industrial applications. Leveraging GaN-on-Si technology and an integrated fast-switching 2.2-MHz gate driver, the new GaN FET families achieve 99% efficiency as per data sheet specifications.

Increasing sales of electric vehicles (EV) is creating a strong demand for compact and lightweight power management solutions. Simultaneously, the availability of more efficient and cost-effective industrial solutions will reduce emissions, contributing to a cleaner environment.

In an interview with Power/EE Times, Steve Lambouses, vice president for high voltage power, and Steve Tom, GaN product line manager, at Texas Instruments, highlighted how the use of new GaN FETs can reduce the size of power management solutions in industrial environments, especially chargers and DC/DC converters in electric vehicles (EVs) where they will contribute to longer battery life.

Industry trends in power
The world’s appetite for energy will continue to grow, while the ability to generate more power will be more limited. Texas Instruments believes semiconductor innovation will enable engineers to do more with less power. “We can see 5 trends in the industry,” said Lambouses. “Power density, increasing power density enables more system functionality at reduced system costs. Low EMI, minimizing interference with other system components and simplifying the engineer’s design ad qualification processes.”

Tom added,”Other topics are Low Iq to extend the battery life, low noise and precision to improve reliability for precision analog applications, and isolation to enable the highest working voltage and highest reliability in high-voltage and safety-critical applications.”

Bipolar and FET transistors find it difficult to cope with high power demands. They can only increase power density if efficiency, form factor and heat dissipation are sacrificed — inefficient switching results in heavy automotive losses. Fast switching technology with wide bandgap materials offers benefits that include reduced system size and cost, as well as increased efficiency. GaN can operate at high temperatures and voltages, helping to efficiently meet a wide range of communications and industrial designs.

“So to optimize the efficiency, we push the switching frequency with the integration, and we can do this because the packaging inductances are small,” said Tom.

One of the challenges in the field of electric vehicles is fast and efficient charging. GaN technology can offer fast charging that uses energy much more efficiently.

In an electric vehicle, efficient energy management involves the battery and its charging, the safety of the batteries themselves, and the cost-effectiveness of the product. Lithium-ion batteries can account for 30% of the cost of a vehicle, and “GaN-based solutions can reduce losses by more than 40%,” says Lambouses. Because of GaN’s greater switching capabilities, it can convert higher power levels more efficiently with fewer components, as shown below in Figure 1.

Figure 1: Comparing the power density of the magnetics of silicon designs vs. GaN designs (Source: Texas Instruments)
Figure 1: Comparing the power density of the magnetics of silicon designs vs. GaN designs (Source: Texas Instruments)

GaN FET solutions
In large-scale power systems, “standard” FETs are used separately from their gate drivers due to different process technologies. This creates additional parasitic inductance, limiting the switching performance of the GaN. Common source inductance significantly increases switching losses.

TI’s new family of industrial 600-V and 650-V (the latter for automotive) GaN devices integrates a GaN FET, driver, and protection functions at 30 and 50-mΩ power stages to provide a single-chip solution for applications ranging from sub-100 W to 22 kW.

“A GaN FET with an integrated gate driver, such as the LMG3425R030, can minimize parasitic inductance at a slew rate of 150 V/ns, while providing 66% lower third-quadrant losses and higher EMI attenuation than discrete GaN FETs,” said Tom.

Figure 2: The integration of a 600-V GaN FET with a gate driver and short-circuit protection (Source: Texas Instruments)
Figure 2: The integration of a 600-V GaN FET with a gate driver and short-circuit protection (Source: Texas Instruments)

When considering the long-term impacts, this implementation, as highlighted by TI, becomes particularly relevant to efficiency. The new GaN FETs reduce conversion losses and simplify thermal control design.

“The integration of over-current and over-temperature protection features protects the system against common power supply fault conditions by offering self-monitoring,” said Lambouses.

A highly integrated GaN device can more effectively increase the reliability and optimize the performance of high-voltage power supplies by integrating functional and protection features. Unlike silicon MOSFETs, GaN conducts in the third quadrant in ‘diode-like’ mode and minimizes dead time by reducing voltage drop. TI’s ideal diode mode in the LMG3425R030 and LMG3425R050 further minimizes losses in power delivery applications.

“The main benefits of these solutions can be summarized in the following points: it enables twice the power output, in a 1U rack server, doubling the power density compared to silicon MOSFETs;  99% efficiency in AC/DC power delivery applications; Integrated, high-speed protection and digital temperature for power supply units (PSUs),” said Tom.

The dead time loss is related to the reverse conduction voltage of the device. For Si MOSFETs, this voltage is determined by its body-diode’s characteristics. For GaN, the reverse conduction voltage depends on the third quadrant characteristic (Figures 3 and 4).

Figure 3: Cross Section Of The Lateral Structure Of GaN FET (Source: Texas Instruments)
Figure 3: Cross Section Of The Lateral Structure Of GaN FET (Source: Texas Instruments)
Figure 4: Simplified Behavior Of GaN in 1st and 3rd Quadrant (Source: Texas Instruments)
Figure 4: Simplified Behavior Of GaN in 1st and 3rd Quadrant (Source: Texas Instruments)

LMG3522R030-Q1 and LMG3525R030-Q1 650-V are automotive-grade of this family. “They reduce the size of electric vehicle (EV) onboard with 2.2-MHz integrated gate driver,” said Tom. All versions have boards for fast implementation in various applications. They are configured to have a socket-style external connection for easy interface with external power stages.

Designers of switching power supplies are continually seeking to increase power density while increasing efficiency. GaN devices enable solutions with higher power density than super junction FETs. But at the same time, they also require careful circuit, process, and material engineering: i.e., high-quality GaN crystal growth, dielectric optimization, and test optimization through new JEDEC JC-70 guidelines for switching reliability evaluation procedures for gallium nitride power conversion devices.

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