High-Voltage SiC FET Repackaged for High Power Density

This article appeared in Electronic Design and has been published here with permission.

Check out our APEC 2023 digital magazine for more show coverage.

Qorvo’s new series of space-saving 750-V silicon-carbide (SiC) FETs offer high efficiency and reliability that’s ideal for space-constrained ac-dc power supplies handling hundreds to thousands of watts.

Part of the company’s UJ4C/SC series, the 750-V SiC FETs are housed in surface-mount TO-leadless (TOLL) packages that are suited for everything from solar inverters and other renewable-energy gear to EV chargers. Ranging from 5.4 to 60 mΩ, the devices are said to have 4X to 10X better on-resistance (R_DS(on))—or the resistance between the drain and source regions of the FET during on-state operation—than alternatives like IGBTs, SiC MOSFETs, and GaN power ICs.

The devices, the first in a new family of 750-V SiC FETs in the TOLL packages, were on display at APEC 2023.

The compactness of the surface-mount package is a boon to power density. Measuring a mere 9.9 × 11.7 × 2.3 mm, the TOLL package is 30% smaller than the industry-standard D2PAK in terms of the amount of space it requires on the circuit board, making for easy placement. The SiC FETs also are half the height of the D2PAK package, while the new package touts better thermal performance and less inductance, too.

Why SiC?

SiC, a wide-bandgap (WBG) semiconductor, has unique physical and electrical properties that help it safely handle higher voltages and currents and lose less power to heat when converting and/or distributing power around a system.

Fast-switching speeds put SiC ahead on the energy-efficiency front. High-speed switching also opens the door to the use of smaller transformers, capacitors, EMI filters, and other passive components that are core building blocks in power supplies. As a result, SiC supports smaller form factors when used in the power electronics at the heart of everything from onboard chargers to solar inverters, which end up weighing less and generating less heat as well.

Qorvo said the new SiC FETs improves on every major figure of merit for resistance and output capacitance, helping curtail conduction loss when they convert power from one level to another in ac-dc or dc-dc power supplies. Thus, they exhibit higher efficiency relative to regular MOSFETs or IGBTs. The 750-V parts have more margin for managing voltage transients compared to 600- or 650-V FETs, while the durability of SiC means that it can tolerate higher operating temperatures.

Other Package Benefits

The new packaging not only saves space on the PCB and prevents excessive power losses, but it also blocks out electromagnetic interference (EMI) more effectively than a switched-mode power supply (SMPS) without it.

Furthermore, the SiC FETs are well-suited for electronic relays, fuses, and circuit breakers that are able to actively monitor load current and input voltage to prevent overcurrent events and block overvoltage spikes. The fast speeds of SiC-based FETs translate to faster response times, which means that the fuse or circuit breaker can shut off very high currents—and even short-circuits—before a system is overloaded.

On top of its high tolerance for heat, the higher thermal conductivity of SiC pulls heat out of the chip more effectively. That opens the door for customers to use smaller heatsinks or passives instead of active cooling. The new SiC FETs support thermal resistance of 0.1°C per watt from the semiconductor’s internal operating area (the junction of the MOSFET) to the case on the package that’s mounted directly to a PCB or heatsink.

The SiC FETs use Qorvo’s unique cascode configuration, in which a SiC JFET is co-packaged with a standard Si MOSFET to deliver a normally-off SiC FET device. The device’s standard gate-drive characteristics allow for the use of off-the-shelf gate drivers. The devices can be safely driven with standard 0 to 12 V or 15 V.

The current rating of the power FETs is 120 A at case temperatures of up to 144°C. The chips also have a high degree of ruggedness, with pulsed current ratings of 588 A up to half a millisecond. Coupled with improvements in conduction loss and heat dissipation, the SiC power devices provide an I²t rating that’s 8X better than a silicon power FET in the same package, increasing its immunity to transient overloads, said Qorvo.

The Kelvin source connection in the package also helps keep EMI in check for high reliability. The new parts include an integrated ESD gate protection clamp.

In addition, the TOLL-packaged devices work with the company’s FET-Jet tool, which allows the instant evaluation of efficiency, component losses, and junction temperature rise for parts in a wide range of ac-dc and isolated and non-isolated dc-dc converter topologies. Single and parallel devices can be compared under user-specified heatsinking conditions to help you select the best solution.

The repackaged 750-V SiC FETs complement the 750-V SiC FETs that the company recently rolled out in 7-lead D2PAK-7L packages for soft-switched dc-dc converters, EV onboard chargers, and data-center power supplies.

Check out our APEC 2023 digital magazine for more show coverage.