eFuses (or electronic fuses) are integrated circuits that can replace large conventional fuses or other protection devices, such as self-healing polymer fuses. They use small plastic packages (such as DFN and flip-chip packages), integrate control loops and low on-resistance power switches, and connect input ports and loads.

　　 When connected in series to the main power line, eFuse works like a standard fuse, has detection capabilities, and responds quickly to over-current and over-voltage conditions. When an overload condition occurs, the device limits the output current to a safe value defined by the user. If the abnormal overload condition persists, the device enters the open state and disconnects the load from the power supply. The overload current limit can be set by an external resistor.

　　 Most eFuses of STMicroelectronics have an input overvoltage clamp function, so it can also provide protection for the load against input voltage deviation caused by power regulation failure.

　　In the process of hot-swapping power supplies or boards when the power is turned on, eFuse increases the output voltage in a linear and controllable manner to prevent high inrush current from the power supply to the load, thereby avoiding power supply overload. This feature is very useful in those applications where a single power supply service is connected to multiple loads on the same power rail (such as HDD arrays and servers). The start time can be adjusted by replacing the soft start capacitor.

　　Efuse electronic fuse

　　 In the eFuses of STMicroelectronics, some devices operate in lockout or auto-retry mode after a failure event. (The fault status signal is sent by the eFuse to the system controller through the fault pin.) The former type can be reset by the user through the reset pin, and the latter type can automatically try to reset after a fault occurs. On STEF01 (a fully programmable universal electronic fuse), the user can set this mode through an automatic pin.

　　Different from traditional circuit protection, eFuse provides faster and more accurate intervention, no need to replace after activation. Typical applications of eFuse are HDD/SSD arrays and servers, industrial and network hot-swappable boards, and devices powered by a separate external AC adapter.