As electric vehicles are equipped with 400- to 800-V battery packs, the power systems under the hood require a way to protect the high-voltage distribution and loads from hazards.
Microchip is offering a faster form of circuit protection with a series of SiC-based high-voltage electronic fuses targeted at EVs that feature a continuous current rating of up to 30 A.
I had the opportunity to check out one of the reference designs, which I walk through in the video above. The model I reviewed integrates all of the building blocks of a high-voltage e-fuse, including automotive-grade, 1,200-V silicon-carbide (SiC) MOSFETs at the heart of the unit.
A PIC microcontroller (MCU) controls the device and connects to the 1.5-A gate driver that turns the FETs on and off. Voltage, temperature, and current sensing are also part of the package.
The device exhibits the advantages of SiC, including its high-frequency switching properties, which gives it the ability to detect and interrupt overcurrent faults faster. The rapid response times reduce peak short-circuit currents from tens of thousands to hundreds of amps, preventing a fault from causing a hard failure. It can tolerate short-circuits for up to 10 µs.
The overcurrent protection capabilities of the high-voltage electronic fuse is represented by its time-current characteristic (TCC) curve, which plots the response time as a function of current.
The curve in this case is formed by three detection methods, depending on the response times required and the level of current traveling through the system. It can use current measurements sampled by the core independent peripherals (CIP) of the MCU to identify overcurrent faults. Alternatively, high currents can be flagged by estimating the junction temperature of the SiC power FETs. Lastly, in case of a short circuit, hardware-based current measurements are used.
The electronic fuse, now shipping in sample quantities, features a LIN communication interface that enables easy configuration of the overcurrent trip characteristics, said Microchip.
Unlike standard fuses that must be ripped out and replaced after being used, the advantage of an electronic fuse is that it’s resettable, which reduces system complexity. Shocks, arcing, and contact bounce that can take a toll on reliability over time are lesser issues when using e-fuses.
The board also supports Microchip’s MPLAB X IDE for software development and debugging.
In the end, the reference design is useful as a development tool, giving you a window into how e-fuses work when used in high-voltage power-distribution systems. Microchip said the e-fuse is not only suited for EV systems, but it can also shine in dc smart grids, EV chargers, and other markets.