SiC Solutions Extend the Range of High-Power Applications

­The demand for power devices is constantly increasing, driven by the impulse coming from sectors with major innovation such as e-mobility, renewable energy, and data centers. Power applications today have continuously more stringent requirements, linked above all to achieving higher efficiency (with consequent reduction of power losses), together with a reduction in weight and size.

Traditional silicon-based MOSFETs and IGBTs, which have been constantly developed and improved over the years, demonstrate their limitations in power applications in which higher switching frequencies, higher heat-dissipation capacity, reduced weight, and smaller footprint are required.

Silicon carbide (SiC) is a wide-bandgap semiconductor that overcomes the limits of Si technology due to its ability to operate at higher voltages, frequencies, and temperatures without being damaged. More than 10 years after its introduction on the market, SiC has now reached a maturity and reliability that allow its use in the most critical power applications, like automotive, renewable energy, data centers, and aerospace.

Microchip has developed rugged SiC MOSFETs with a higher repetitive Unclamped Inductive Switching (UIS) capability; negating the need to add a snubber to protect the SiC MOSFET from overvoltage stress (avalanche). When the current flowing through an inductance is abruptly interrupted, the magnetic field induces a counter electromotive force, which can generate very high voltages across the MOSFET itself. For power devices, it is therefore essential to achieve a high degree of ruggedness, understood here as the ability to resist SiC MOSFET degradation when subjected to UIS; otherwise additional components are needed to protect the SiC MOSFET from avalanche. In addition to their ruggedness, Microchip SiC MOSFETs solutions offer “IGBT-like” short circuit performance to withstand unexpected system transients.

To meet the requirements of power applications that use high switching frequencies and high operating voltages to increase efficiency and reduce the weight and size of the solution (such as electrified transportation, renewable energy, aerospace, and industrial applications), Microchip’s new 3.3 kV SiC MOSFETs include R_DS(on) (down to 25 mΩ), and SiC SBDs that feature a current rating of up to 90A.

Although 3.3 kV IGBTs are currently used in numerous applications, their switching speeds are limited, resulting in high switching losses and large system size. The use of 3.3 kV SiC MOSFETs allow designers to reduce losses, size, and weight of the solution; and reduce the complexity of multi-level system to simply 2-level designs.

SiC: Advantages and Applications

Compared with traditional Si power devices, such as MOSFETs and IGBTs, Microchip’s SiC solutions offer:

·       Higher junction temperature and improved cooling, Lower R_DS(on) and higher efficiency

·       3× higher thermal conductivity, resulting in higher power density and higher current capabilities

·       2× higher electron saturation velocity, resulting in faster switching and size reduction (in addition, higher switching frequency enables smaller magnetics, transformers, filters, and passives, reducing the footprint of the solution)

·       Lower switching losses

·       10× lower failure-in-time rate for neutron susceptibility than comparable IGBTs at rated voltages

·       Extremely low parasitic (stray) inductance, at <2.9 nH in SiC modules

The typical markets and applications addressed by Microchip’s SiC products are:

·       Transportation: The high robustness and operating voltage of SiC devices is essential for creating efficient voltage inverters and converters, as well as protection devices, used in electric vehicles (cars, buses, trucks, rail, boats, eVTOL, and planes), and the charging infrastructure.

·       Industrial: High switching frequency, low losses, and excellent thermal management make SiC devices the ideal solution for applications such as motor control, switching power supplies, UPS, welding, and induction heating.

·       Renewable energies: SiC-based inverters can be used in photovoltaic applications and in wind turbines to reduce power losses and increase efficiency.

·       Medical: Reliable, robust, and efficient power supplies are required in diagnostic equipment, such as MRIs and X-rays.

·       Aerospace and defense: The properties of SiC allow power devices based on this material to operate at high voltages and high temperatures without being damaged. Microchip’s SiC product portfolio includes the BL1, BL2, and BL3 family of baseless power modules, which have passed multiple validation tests compliant with the RTCA DO-160G standard and are now qualified for aerospace applications, including cargo and heavy drones.

The comparison between how R_DS(on) varies with temperature in Si and SiC is quite significant. In Si MOSFETs, the temperature dependence of the R_DS(on) (shown in Figure 2) does not vary with the rated voltage of the device, as the electron mobility in Si MOSFETs is dominated by thermal scattering. In the temperature range between 25˚C and 150˚C, R_DS(on) increases at a ratio of about 2.7 to 1.

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Figure 2: RDS(on) vs. temperature in Si MOSFET

In Figure 3, instead, we can observe the same type of curve referred to a 1200V SiC device belonging to the Microchip family. In this case, in the temperature range between 25˚C and 175˚C, R_DS(on) typically varies with a ratio between 1.5 and 1.8. Therefore, compared with the previous one, it is an almost flat curve.

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Figure 3: RDS(on) vs. temperature in SiC 1200V device

Digital Programmable Gate Drivers

To solve the critical challenges that might arise when operating SiC and IGBT power devices at higher switching frequencies, Microchip has designed the AgileSwitch family of configurable digital gate drivers. In particular, SiC MOSFETs need to be controlled by properly setting the right gate drive parameters. Otherwise, turn-off spikes, ringing, electromagnetic interference, and DSAT might cause permanent damage to the device.

The AgileSwitch drivers allow designers to control, monitor, and protect SiC-based applications with Augmented Switching technology, providing up to seven fault notifications and protection for safe and reliable operation. Microchip offers a full line of module adapter boards and gate-driver cores, along with their plug-and-play gate-driver boards to address a wide range of SiC power modules.

Figure 4 shows an AgileSwitch SiC dual-channel gate driver core for 1200V SiC modules. The gate-driver cores, which integrate the Augmented Switching control technology, feature robust short-circuit protection and are fully software-configurable, including ±V_gs gate supply voltages. Because SiC devices can withstand short-circuit for a much-reduced period (about 2–3 µs), it is essential to adopt the appropriate short-circuit protection parameters for the gate driver.

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Figure 4: Dual-channel configurable digital gate driver core for 1200V SiC

Unlike conventional analog gate drivers, these digital gate drivers can switch up to 200 kHz are fully software configurable and prevent false faults and mitigate ringing, Electromagnetic Interference (EMI) as well as overshoot and undershoot in SiC and IGBT power modules. Plugged into the module adapter board, the digital gate driver core allows designers to quickly evaluate module and gate driver and reduce time to market.

The gate driver shown in Figure 4 provides up to 10A of peak current and includes an isolated DC/DC converter (with configurable output voltage) and low-capacitance isolation barrier for PWM signals and fault feedback. The Intelligent Configuration Tool (ICT) is a GUI that allows users to quickly configure the relevant gate driver parameters without having to worry about changing hardware. The configurable features include Augmented Switching turn-on and turn-off, ±V_gs gate voltages (V_gs positive from 15 V to 21 V, V_gs negative from –5 V to 0 V), power supply under- and overvoltage lockout, desaturation detection settings, dead time, fault lockout, and reset settings.

Tools and Development Kits

Microchip’s SiC portfolio is supported by a wide selection of SiC SPICE models compatible with the MPLAB Mindi analog simulator modules and driver board reference designs. Additionally, the Intelligent Configuration Tool (ICT) enables designers to set the relevant SiC gate-driver parameters for Microchip’s AgileSwitch family of configurable digital gate drivers. The ICT interface allows designers to configure several gate driver parameters, including the gate switching profiles, system- critical monitors, and controller interface settings. New devices can be quickly and easily characterized, changing the driver settings in the lab or in the field with no soldering required. The result is a gate driver customized and optimized to meet the application’s requirements without having to change hardware. To further speed time to market, ASDAK (without SiC module) and ASDAK+ (with SiC module) accelerated development kits include the hardware and software elements required to optimize the performance of SiC power modules and systems, saving designers development time on new designs.

Microchip Technology