The use of gallium nitride (GaN) in power applications is an important innovation that promises to make a significant contribution to the goal of efficient power conversion. GaN is a semiconductor material that is already in use and is widely used in LED lighting and the increasingly important wireless field. With the advancement of technology and the improvement of failure rate, GaN provides many advantages in applications such as AC and DC power conversion and level conversion.
GaN-based switching power transistors can operate at high voltages with higher performance and lower losses than previously used silicon (Si) transistors.
GaN can operate under high frequency conditions and maintain high performance and efficiency. GaN devices use a GaN-on-Si process that is suitable for existing Si manufacturing processes. Because GaN devices are much smaller with the same current capability.
As a result, GaN transistors are more cost-effective than Si equivalents, making GaN devices attractive for applications ranging from large industrial equipment to miniaturized handheld devices. High-performance power supply design not only requires higher operating frequency, but also achieves precise switching characteristics, and the huge advantages of GaN are driving the advent of the era of efficient power conversion.
Today, power supply designers are beginning to rethink their circuit designs, looking for ways to power systems that can fully exploit the potential of new GaN transistors while avoiding harmful effects.
Traditional solutions usually start with the components themselves, such as GaN switches, Si switch drivers, high-speed switching controllers, power inductors, transformers and capacitors; integrated circuit (IC) manufacturers developing power products can do this by providing collaborative systems level solutions, achieving substantial performance design improvements for customers, and even integrating multiple chips into modular packages.
GaN’s place in the power supply chain
Most electronic equipment uses switching power supplies (SMPS), which can effectively convert alternating current to direct current (AC to DC) and step voltages 110-120V, 220-240V or 12-, 5-, 3.3-V, etc. required by the system Power supply range;
These functions are typical for consumer electronics and data centers. SMPS are also used in DC-to-DC conversion and renewable energy inverters, automotive electronics, industrial equipment and other types of high-power systems.
Figure 1 shows a typical SMPS workflow diagram. SMPS rectifies the input voltage (usually high-voltage and low-frequency alternating current) into DC. The power line filter is used to prevent the high-frequency components generated in the power supply from being reflected back during the transmission process. The high-frequency power switch (the core of SMPS) converts DC The signal is converted into a pulse voltage waveform and stabilized and filtered for output at the level required by the low-voltage system.
A feedback controller from the output is used to provide a pulse-width modulated (PWM) signal to the power switch driver to achieve regulation; the signal pulse width gradually increases or decreases as load demand changes.
Traditionally, power switches have used silicon MOSFETs (metal oxide semiconductor field effect transistors), but they are now being replaced by GaN FETs.
Depending on the system design requirements, a variety of topologies can be used, ranging from singleFET boost converters to multiple dual-FET designs, up to 4 FET full-bridge converters, in the arrangement of power switches.
Switches and their drivers are very sensitive parts of the entire design because they must perform every operation exactly as instructed by the controller, otherwise the operation of the power system will become unstable.
In addition, noise is injected into the feedback loop due to the rapid rise and fall of the modulation voltage, which can also cause instability in the power supply system. A requirement of all grid-connected systems is to isolate the parts coming from the grid and the parts provided to the power system to ensure the safety of user equipment.
Another problem is that high-frequency operations during the power conversion process cannot be allowed to interfere with the transmission of grid energy and generate unnecessary noise on the power transmission lines.
GaN devices solve this isolation requirement through conversion operations at higher frequencies, effectively reducing the impact of electromagnetic interference; conversion at higher frequencies can reduce the size of isolation transformers and input filters.
Advantages of applying GaN in SMPS systems
In the application of power switches, GaN has more important advantages than silicon materials because GaN can provide lower losses at higher voltages and use less energy when switching. After years of development, Si switches have been greatly improved, but under the same size and voltage conditions, GaN has excellent performance that cannot be matched by Si devices.
Currently, Si MOSFET has certain cost advantages compared with GaN, but as time goes by, the cost difference will become smaller and smaller.
The operating voltage range of GaN switching devices is very wide, so power supply designers can achieve higher switching frequencies over a wide input and output voltage range while achieving the desired design efficiency in a smaller physical size. The most valuable application of GaN is in power solutions that are as miniaturized as possible.
Figure 2 shows the basic structure diagram of a GaN transistor. From the previous discussion, we can know that the GaN material is located on the Si substrate. The advantage of this design is that it can fully utilize the advantages of decades of Si processing and take advantage of the specialties of the new material GaN. One of the benefits is that it can achieve higher bandgap voltage.
Semiconductors are a special class of materials because the band gap energy is the voltage jump required to change the material from an insulator to a conductor. The bandgap energy of 3.2 electron volts (eV) offered by GaN is almost three times that of Si.
In theory, higher bandgap energy means better performance at higher temperatures because more heat can be held before the substance becomes a conductor; this inherent property is expected to improve cars, Device performance in industrial and other high temperature environments.
GaN Development Curve in SMPS Design
Although GaN has many advantages, the technology is only just starting to make its way into power supply design. Previous applications in LED and wireless fields may give people the impression that GaN is already well-positioned for application in power supply design.
In fact, using GaN in power FETs requires significant process and device development, making the development of such products slow. The differences between new FETs and Si devices make IC suppliers and system designers act cautiously during the development phase and gradually solve various complex problems encountered in the design.
Traditional GaN devices are typically on or in depletion mode, while silicon MOSFETs are enhancement-mode devices that are off. To provide drop-in replacements for silicon MOSFETs, GaN FET switch suppliers have redesigned their products to operate in enhancement mode or use a series switch to provide normally-off functionality.
Replacing Si MOSFETs with GaN FETs is just the beginning of a redesign. The high-frequency capabilities of GaN transistors require greater timing accuracy in switch drive signals. In addition, switches are highly sensitive to parasitic impedances from packaging, interconnects, and external sources.
Integrated Si-based GaN drivers can turn GaN switches on and off at high speeds, helping to advance the design of GaN switching power supplies. Mature silicon processes enable the development of these extremely precise, high-frequency tunable drivers.
For example, TI's LM5113 gate driver is designed to control mid- to high-level high-end and low-end enhanced GaN power switches. The gate driver integrates the required components to achieve performance optimization. This integration can not only reduce the circuit board Space can also help simplify the design.
In addition to enabling high-precision drive timing with minimal latency, the device also provides critical protection for efficient and precise operation of GaN switches. For example, a bootstrap clamp keeps the gate-source voltage within a safe operating region; high-current pull-down improves dv/dt immunity and prevents unexpected low-side activation; and independent source and drain pins allow optimization On- and off-times improve efficiency and reduce noise, while fast propagation delay matching optimizes dead time during switching transitions.
GaN-based SMPS system-level solution design
Combined with fast and precise power management control, GaN gate drivers feature highly advanced GaN-based SMPS designs. Therefore, improvements in SMPS performance are limited by how well the gate driver itself is optimized, and even the shortest possible traces between the driver and the GaN switch can cause delay times to vary with the design.
Future IC solutions will need to control variability issues caused by the layout and design of passive components, as these are critical to the coupling characteristics of drivers and switches. Since the two devices discussed above are based on different materials and have very different characteristics, the cost of integrating them on a single chip may still be relatively high in the near future.
However, a single-package module integrating FETs, drivers, and switching-enabled passives (shown in Figure 3) will significantly reduce the SMPS area and component count; this size reduction also means lower system manufacturing costs and GaN Improvement of design efficiency.
As important as reducing the size of the solution is reducing design complexity, driver switch modules will reduce chip-to-chip connection lengths, minimize delay times and parasitic impedances, thereby reducing distortion of the switch output pulse waveform. A well-designed module can greatly reduce the parasitic factors of a multi-chip design, perhaps even by an order of magnitude or more.
Another important factor in providing a system-level solution is the controller-regulator, which must operate at the high frequencies supported by GaN and must respond to changes in output voltage in real time. The time resolution must also meet precise pulse width requirements to minimize conduction losses during dead time.
Fortunately, digital power controllers can support these requirements and provide additional performance and I/O capabilities. TI provides comprehensive expertise in digital power control, combining the company's power technologies to provide system-level solutions for GaN regulation and control switching.
There is also a need to investigate magnetic components based on GaN designs, as these components are currently still customized for silicon-enabled frequencies. TI cooperates with power supply manufacturers and GaN research institutions to continuously propose new design requirements to magnetic component suppliers based on the specific needs of the market.
As the scope of use of GaN power devices continues to expand, magnetic device suppliers will improve existing technologies in a market-oriented manner. Once the time is right, the industry will be able to feel the benefits of GaN devices in many power supply applications.
GaN innovation will meet future market needs
The continuous growth of the world's population and the acceleration of social development have led to an increasing demand for electricity. Increasingly urgent environmental pressure forces us to do more things with less energy. As we try to address these needs, the world will benefit from innovations that help us deliver, convert and consume electricity more efficiently, resulting in technologies that improve our lives.
GaN is one such innovation that promises to reduce power losses in power conversion, thereby helping us get more benefits from limited energy. To address the challenges of GaN, TI is leveraging its leadership in research and development to create solutions that reduce the complexities of high-frequency power conversion. These differentiated solutions will help simplify designs, save space and reduce component count while minimizing signal delays and spurious interference.
With the emergence of these advantageous products, SMPS developers will be able to launch higher-performance systems faster. The success of high-performance systems will further propel GaN into new application areas, including high-power industrial equipment and low-power consumer markets. Modules and other key components of system-level solutions will help us realize the full potential GaN technology offers in terms of power efficiency.
