From Gate Drivers to E-fuse Demonstrators, SiC Devices Target EV Tech
Semiconductor companies are leveraging the properties of SiC to achieve fast switching speeds and improved isolation in new EV designs.
After an unprecedented year of sales in 2022, demand for electric vehicles is only projected to increase in the future. As gas prices rise to astronomical levels, electric vehicles offer an alternative that is both economical and sustainable.
The basic components of a modern electric vehicle. Image courtesy of the National Renewable Energy Laboratory (NREL)
As demand for these vehicles increases, designers are tasked to work with electrical components that can switch high voltages quickly, safely, and efficiently. Below is a roundup of some recently released components and tools to help designers meet the strict safety, efficiency, and performance requirements of up-and-coming EV designs.
TI Leverages SiC for EV IGBTs and Traction Inverters
Recently, Texas Instruments introduced the UCC5880-Q1 SiC gate driver for IGBTs and traction inverters for EVs. The gate driver isolates the high-voltage motor circuitry connected to the output of the traction inverter from the low-voltage electrical components near the input. Without isolation, a current spike caused by the high voltages used in the motor circuitry could severely damage the low-voltage components.
A SiC gate driver isolates low-voltage and high-voltage circuitry. Image courtesy of Texas Instruments
One of the key innovations of the UCC5880 is also the bidirectional SPI communication interface. This allows the system to vary the drive strength (and consequently the SiC slew rate) and optimize the overall efficiency and switching speed by managing the transient overshoot of the gate.
Managing the SiC slew rate is important to overall system efficiency. Image courtesy of Texas Instruments
TI claims that because the UCC5880 allows designers to vary the gate-drive strength in real-time between 20 A and 5 A, system efficiency can improve by as much as 2%. This efficiency can result in an EV that can drive seven more miles on a battery charge and 1,000 more miles a year for an EV driver charging their car three times per week.
Microchip's SiC E-Fuse Demonstrator Stops Fault Currents in Short Order
Microchip is targeting EV design efficiency with a different SiC-based approach. The company's E-Fuse Demonstrator Board uses the fast switching capabilities of SiC to interrupt fault currents in microseconds (approximately 100–500 times faster than mechanical techniques) because of its high-voltage, solid-state nature. This quick response time mitigates hard failures by shrinking peak short-circuit currents from tens of kiloamps to hundreds of amps. The demonstrator comes in six variations for 400 V–800 V battery systems with a current rating of 30 A.
Microchip's SiC-based E-Fuse Demonstrator Board. Image courtesy of Microchip
According to Microchip, designers can sidestep design-for-serviceability limitations with the E-Fuse Demonstrator's reset features. These features streamline vehicle packaging for improved BEV/HEV power system distribution. The demonstrator also includes a built-in Local Interconnect Network (LIN) communication interface to speed up the development time for SiC-based auxiliary uses. With this interface in place, designers can access diagnostic status and configure over-current trip characteristics without changing any hardware components.
Onsemi Reveals Fast-switching MOSFETs and Half-bridge PIMs
Also homing in on EV efficiency is Onsemi, with a new SiC product portfolio that aims to handle up to 1200 V—a significant increase over previous product families. Included in this new portfolio are EliteSiC MOSFETs and modules for higher switching speeds common in 800 V EV onboard chargers and energy infrastructure use cases. These include solar and energy storage systems and EV charging.
Schematic diagram of the NXH003P120MNF2, one of the devices in the 1200 V EliteSiC MOSFET family. Image courtesy of Onsemi
Onsemi is also eyeing industrial applications with its new portfolio—namely, with the new EliteSiC M3S devices in half-bridge power integrated modules with an "industry-leading lowest RDS(on)." The devices are described as "highly integrated" and include direct bonded copper designs to balance current sharing and thermal distribution between parallel switches, a desirable feature in DC-AC, AC-DC, and DC-DC high-power conversion stages.
The 1200 V EliteSiC MOSFETs are automotive qualified and built for high-to-low voltage DC-DC converters and high-power onboard chargers up to 22 kW.
Why SiC Holds Its Popularity in EV Designs
Several properties of SiC (silicon carbide) make it suitable for electric vehicle applications versus other semiconductor compounds. These include its high thermal conductivity, breakdown voltage, bandgap energy, and electron mobility. The high breakdown voltage and band gap energy of SiC make it good for high-voltage designs, while better electron mobility and thermal conductivity allow for faster switching speeds and heat transfer.
These performance benefits are significant considering the number of high-voltage systems in an EV: consider the high-voltage DC battery, an AC motor to drive the wheels, DC electrical components for interior and exterior features (such as the infotainment system and headlights), and a thermal cooling system. In such systems, a DC-DC buck converter steps down the high main battery voltage for other lower-voltage DC components. A traction inverter converts the DC battery voltage to an AC voltage for the motor. And a traction inverter with insulated-gate bipolar transistors (IGBTs) can switch rapidly and convert DC to AC.
Finally, all high-voltage circuits in the system require protection since the DC battery voltage is generally very high (>400 V). A short circuit condition could cause severe damage to this system without such protection.
Block diagram showing the location of a traction inverter within an EV. Image courtesy of Texas Instruments
With these strict constraints in mind, it's no wonder why semiconductor manufacturers like TI, Microchip, and Onsemi are targeting SiC, whether they're developing high-voltage MOSFETs or demonstrator tools for testing.