“The physical properties of gallium nitride (GaN) semiconductors are comparable to those of silicon devices. Traditional power supply metal-oxide-semiconductor field-effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs) can increase power density only at the expense of efficiency, form factor, and heat dissipation.
The physical properties of gallium nitride (GaN) semiconductors are comparable to those of silicon devices. Traditional power supply metal-oxide-semiconductor field-effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs) can increase power density only at the expense of efficiency, form factor, and heat dissipation.
Using GaN enables faster processing of power electronics and more efficient powering of an increasing number of high-voltage applications. GaN’s better switching capability means it can convert higher levels of power more efficiently with fewer devices, as shown in Figure 1. GaN semiconductors enable new power and conversion systems in AC/DC power supply applications. (For example, 5G communications power rectifiers and server computing) GaN continues to push the boundaries of new applications and is beginning to replace traditional silicon-based power solutions in the automotive, industrial and renewable energy markets.
Figure 1: Magnetic power density comparison between silicon design and GaN design
GaN FETs: New Integrated Systems
Large data centers, enterprise servers, and communications switching centers consume large amounts of power. In these power systems, the FETs are often packaged separately from the gate drivers because they use different process technologies and end up creating additional parasitic inductance.
In addition to resulting in larger form factors, this may also limit the switching performance of GaN at high slew rates. On the other hand, TI GaN FETs with integrated gate drivers, such as the LMG3425R030, with a slew rate of 150V/ns, reduce parasitic inductance to a greater extent, reduce losses by 66% compared to discrete GaN, and Electromagnetic interference is minimized. Figure 2 shows a TI GaN FET with an integrated gate driver.
Figure 2: Integration of a 600V GaN FET with gate driver and short-circuit protection
In data centers and server farms, TI’s new GaN FETs enable simpler topologies (such as totem-pole power factor correction), resulting in lower switching losses, simplified thermal design and reduced heat sink size. These devices achieve twice the power density and 99% efficiency compared to silicon MOSFETs in a 1U rack server of the same size. This power density and efficiency savings becomes especially important when considering the long-term impact. For example, suppose a server farm improves AC/DC efficiency by 3% per month by installing GaN devices. If that server farm were converting 30kW of power per day, they would save over 27kW per month, which is about $2,000 per month and $24,000 per year.
When GaN FETs are integrated with current limiting and thermal detection, it prevents shoot-through and thermal runaway events. In addition, system interface signals enable self-monitoring functions.
Reliability is a critical factor in power electronics. Therefore, highly integrated GaN devices can more effectively improve reliability and optimize the performance of high-voltage power supplies by integrating functions and protection functions compared to traditional cascaded and stand-alone GaN FETs.
With external drivers, parasitic inductance can cause switching losses as well as ringing and reliability issues at high GaN frequencies. Common source inductance greatly increases conduction losses. Likewise, designing robust overcurrent protection circuits at high slew rates is difficult and expensive. However, since GaN itself lacks a body diode, it reduces ringing on the switch node and eliminates any reverse recovery losses.
GaN device with protection function
The structure of GaN devices is very different from that of silicon devices. Although they can switch more quickly, they still face unique challenges from a performance and reliability standpoint. There are also issues such as design simplicity and bill of materials cost when using discrete GaN devices.
The new family of industrial 600V GaN devices integrates GaN FETs, drivers and protection functions at the 30-50mΩ power stage, providing a single-chip solution for 100-10kW applications. The LMG3422R030, LMG3425R030, LMG3422R050 and LMG3425R050GaN devices target high power density and high efficiency applications.
Unlike silicon MOSFETs, GaN can conduct in the third quadrant in a “diode-like” manner and minimize dead time by reducing the voltage drop. TI’s ideal diode mode in the LMG3425R030 and LMG3425R050 further reduces losses in power delivery applications. Please read the application note “Optimizing GaN Performance Using Ideal Diode Mode” for more information.
These GaN devices have passed 40 million hours of device reliability testing, including accelerated switching testing and in-application hard switching testing. These reliability tests are performed under highly accelerated switching conditions at maximum power, voltage, and temperature.
Designers of switching power supplies are constantly striving to increase power density and efficiency. Silicon MOSFETs and IGBTs have lower power density and efficiency, and silicon carbide (SiC) devices have higher power density and efficiency, but also cost more.
GaN devices enable solutions to achieve twice the power density of premium superjunction FETs. Likewise, they facilitate certification to standards such as 80Plus Titanium, which require very high power efficiency for server and communications applications.
Although GaN is a revolutionary technology in power electronics, it still requires careful process and materials engineering. This requires building high-quality GaN crystals, optimizing dielectric films and ensuring very clean interfaces in the fabrication process. In addition to this, skilled testing and packaging is a must.