With the emergence of new power switching technologies based on materials such as silicon carbide (SiC) and gallium nitride (GaN), performance is better and power is higher than ever before, and so is the gate driver matched with it. This article will show you some of the major differences between GaN and SiC switches and IGBT/MOSFETs, how gate drivers will support them, and introduce the gate driver solutions introduced by ADI.
New power switching technologies can be in line with high power applications
For many years, the choice of power switching technologies for power output systems has been very simple. At low voltage levels (usually below 600 V), MOSFET is usually selected, and at high voltage levels, IGBT is usually more selected. With the emergence of new power switching technologies in the form of SiC and GaN, this situation is changing.
These new switching technologies have many obvious advantages in performance. The higher switching frequency can reduce the size and weight of the system, which is very important for photovoltaic inverters used in energy applications such as solar panels and target markets such as automobiles. Increasing the switching speed from 20 kHz to 100 kHz can greatly reduce the weight of the transformer, thus making the motor of the electric vehicle lighter, allowing it to travel longer distances, and reduce the size of the inverter used in solar energy applications, thus making it more suitable for industrial applications. In addition, higher operating temperatures (especially GaN devices) and lower power -on drive requirements can also simplify the design work of system architects.
Like MOSFET/IGBT, these new technologies are in their infancy and seem to be able to meet different application requirements. Until recently, GaN products were usually in the 200 V range. Although these products have developed rapidly in recent years and there are many products in the 600 V range, this is still far from the main range of SiC (close to 1000 V), which shows that GaN has naturally replaced MOSFET devices and SiC has replaced IGBT devices. Since superjunction MOSFETs can bridge this gap and realize high voltage applications up to 900 V, in certain GaN research and development, devices capable of handling applications with voltages above 600 V are now available.
New power switching technologies have pros and cons
Although the advantages brought by the new GaN and SiC power switching technologies are extremely attractive to designers, they are not without cost. First and foremost is the increase in cost. The price of this device is several times higher than that of equivalent MOSFET/IGBT products. IGBT and MOSFET production is a well-developed and highly understood process, which means that compared with their new rivals, their costs are lower and their price competitiveness is higher. At present, compared with their traditional rivals, the prices of SiC and GaN devices are still several times higher, but their price competitiveness is continuously improving.
Higher switching frequency also creates common-mode transient immunity, which is a very serious problem for system designers. The high slew rate signal coupled with the isolation barrier in the isolated gate driver may corrupt data transmission, resulting in unwanted signals at the output. In traditional IGBT-based systems, gate drivers with immunity between 20 kV/s and 30 kV/s are sufficient to withstand common-mode interference. However, GaN devices often have slew rates that exceed this limit. In selecting a gate driver for a stable system, its common-mode transient immunity shall be at least 100 kV/s.
International regulations drive demand for isolated gate drivers
New international regulations on motor energy efficiency are accelerating the migration from fixed speed, direct online induction motors to inverter controlled machines. A common requirement is an IGBT gate drive and some form of current measurement at a minimum for protection in simple open-loop inverters, through to high fidelity current control in drives and servos.
This trend toward even more efficient motors is increasing the demand for IGBT-based frequency inverters that transform the rectified mains input into the variable frequency voltages that drive the motor. Inverter controlled motors have the output torque or speed optimally matched to the shaft load to minimize energy consumption, reduce motor running temperatures, and improve motor reliability. Isolation technology is a critical element in the drive system since it safely isolates the controller user interfaces from the dangerous high voltages connected to the inverter.
There are generally two approaches to addressing the induced turn on of inverter IGBTs—using bipolar supplies and/or the addition of a Miller clamp. The ability to accept a bipolar power supply on the isolated side of the gate driver provides additional headroom for the induced voltage transient.
ADI gate driver solves difficulties in new power switching technologies
In view of the rapid development of new power switching technologies, ADI has also introduced corresponding gate drivers to cope with it. For example, the ADuM4135 uses ADI's iCoupler® technology to provide common-mode transient immunity up to 100 kV/s, which can cope with such applications. However, improving CMTI performance often results in additional delays. The increased delay means increased dead time between the high-side and low-side switches, which reduces the performance. This is especially true in the field of isolated gate drivers, where signals are transmitted over the isolation barrier and generally have a longer delay. However, the ADuM4135 not only provides 100 kV/s CMTI but also has a propagation delay of only 50 ns.
The ADuM4135 is a single-channel gate driver optimized specifically for driving IGBTs. ADI's iCoupler® technology supports isolation between the input signal and the output gate driver. The ADuM4135 provides Miller clamping for robust IGBT single-rail power shutdown at gate voltages below 2 V. It can operate with unipolar or bipolar secondary supplies with or without Miller clamping. ADI’s chip-scale transformers also provide isolated communication of control information between the high and low voltage domains of the chip. The chip status information can be read back from the dedicated output to control the reset of the device when a secondary power failure occurs on the primary side of the device.
In addition, the ADuM4135 integrates a desaturation detection circuit to provide protection for high voltage short-circuit IGBT operation. Desaturation protection includes noise reduction features, such as a masking time of 300 ns after masking the voltage spikes due to initial start-up switching events. The internal 500 µA current source ensures a small number of devices. However, to improve the noise immunity level, the internal blanking switch also supports the addition of an external current source, with the secondary undervoltage lockout (UVLO) set to 11.67 V and the common IGBT threshold level noted. The ADuM4135 can be used in MOSFET/IGBT gate drivers, photovoltaic inverters, motor drives, power supplies, and other fields.
The ADuM4135 supports 4A peak drive output capability, with the resistance of the output power device less than 1 Ω, supports desaturation protection, provides isolated desaturation fault reporting, has soft shutdown capability on fault and Miller clamping output with gate sense input, supports isolated fault and readiness function, has a low propagation delay of only 55 ns (typical), and has a minimum pulse width of 50 ns, and operates at the temperature range of − 40 ℃ to + 125℃.
ADI_EVAL-ADuM4135EBZ
The ADuM4135 has an output voltage range of 30V and an input voltage range of 2.3 V to 6 V, supports output and input undervoltage lockout (UVLO), has a creepage distance of 7.8 mm (minimum), a common-mode transient immunity (CMTI) of 100 kV/µ s, a lifetime of 20 years at 600 Vrms or 1092 V DC operating voltage, complies with safety and regulatory certification, 5 kV AC a minute per UL 1577 compliant, supports CSA component acceptance notification 5A, DIN V VDE V 0884-10 (VDE V 0884-10): 2006-12 and V IORM = 849 Vpeak (reinforced/basic). In addition to speeding up customer product development, ADI has also introduced a matching evaluation kit EVAL-ADuM4135EBZ as an option for customers.
Conclusion
The application of GaN and SiC devices in power conversion has been long considered, and now it has finally come true. Although this technology can provide attractive advantages, they come at a cost. In order to provide excellent performance, the new switching technologies need to change the requirements of the isolated gate driver used and will bring new problems to system designers. ADI's ADuM4135 can help solve this problem and make it easier to develop related products. It will be the best ready-made and feasible solution for GaN and SiC.
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