eFuse

In electric and hybrid vehicles, many fuses i.e. conventional thermal fuses are used to protect systems such as onboard chargers, auxiliary systems, BMS, and junction boxes.

Fuses are a well known, common solution for the system protection of electric machines, which are relatively robust against overcurrent. However, in order to avoid damage to power semiconductor devices such as SiC and GaN used in onboard chargers against surge currents such as short-circuits that occur in the order of microseconds, the accuracy of fusing current and order of milliseconds of fusing time may not be sufficient. The new eFuse system, which detects such a surge current that could damage the devices precisely within the order of nanoseconds and cuts off the current, will be the key to protecting systems in next-generation EVs.

The eFuse project introduces a new eFuse system, which achieves a short-circuit detection response time of 160ns or less under the test condition of 650A of short-circuit current in an 800V system.

Project goals

The eFuse system is designed to handle different modes of operation, i.e. short-circuit and overcurrent, and generates current cutoff triggers in three circuits: short-circuit detection, dI/dt detection, and overcurrent protection. This circuit configurations allow better current turn-off controls for different operating modes, resulting in a more flexible protection system than a fuse.

Fast and accurate current detection is necessary to protect against damage to SiC, GaN, and other semiconductor power devices due to short-circuit currents and other causes. In this project, we adopted the CZ39xx series’ current sensor from Asahi Kasei Microdevices, which is ideal for this application with a 4MHz bandwidth, less than 100ns of response time, and fast settling from switching noise. It is also robust to strong magnetic fields of over several hundred milli-Tesla. These circuits employing CZ39xx series current sensor, peripheral circuits including control logics, and semiconductor switches composed of SiC power devices are mounted on a single compact PCB.

This has resulted in eFuse, an elegant protection device that can be resettable without replacing any components, and has cut off characteristics that match the cause of abnormal currents, such as short circuits or overcurrent.