eFuses, or electronic fuses, are integrated circuits that can replace larger conventional fuses or other protection devices such as resettable polymeric fuses. Housed in small plastic packages, such as DFN and Flip-chip, they integrate a control circuit and a power switch with low on-resistance, connecting the input port to the load.
When connected in series to the main power rail, an eFuse operates like a standard fuse with the ability of detecting and quickly reacting to overcurrent and overvoltage conditions. When an overload condition occurs, the device limits the output current to a safe value defined by the user. If the anomalous overload condition persists, the device goes into an open state, disconnecting the load from the power supply. The overload current limit can be programmed by means of an external resistor. An input overvoltage clamp function is available in the majority of ST's eFuses, therefore the load can also be protected against power supply regulation failure leading to input voltage excursion.
At turn-on, during power hot-plug or hot swapping of boards, the eFuse ramps up the output voltage in a linear and controlled way, which prevents a high inrush current flowing from the power source to the load, consequently avoiding power supply overload. This function is very useful in applications where a single power supply serves several loads connected to the same rail, such as HDD arrays and servers. The startup time is adjustable by changing a soft start capacitor.
The STEVAL-EFUSE01 allows full evaluation of the STEF01 E-fuse and is designed to help you test and develop a power path protection to the system. The STEF01 E-fuse integrates a control circuit and a low on-resistance MOSFET switch and provides a full set of protections, including overcurrent, overvoltage and inrush current. You can adjust UVLO threshold, clamping voltage and overload current limits through mechanical trimmers.
An external MOSFET, driven by the STEF01 gate driver pin, can be mounted to implement a reverse-current blocking circuit. The inrush current can be controlled by the output voltage ramp rate, with the dedicated soft start circuit embedded in the STEF01 device. The STEVAL-EFUSE01 evaluation board lets you easily adjust the output voltage ramp rate at the desired startup time, by changing the Cdv/dt capacitor.
As most applications require a flag to signal that the output voltage is in the correct range, the STEVAL-EFUSE01 features a PG test point for information about the voltage drop on the pass element. The STEVAL-EFUSE01 also features thermal latch and auto-retry thermal protection modes, selectable through a dedicated jumper configuration.
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