The STEF4S is an integrated electronic fuse optimized for monitoring the output current and the input voltage. It can be connected in series to 3.3 V or 5 V rails, protecting the electronic circuitry on its output from overcurrent and overvoltage. The operating mode (5 V or 3.3 V) can be selected by a dedicated pin. The STEF4S has a controlled turn-on time, adjustable by an external capacitor. When an overload condition occurs the device limits the output current to a predefined safe value. If the anomalous overload condition persists it goes into an open state, disconnecting the load from the power supply. If a continuous short-circuit is present on the board, the E-fuse limits the output current to a safe value.
In case of overvoltage on the input, the device clamps the output voltage to a predefined value and protects the load.
If the anomalous fault condition persists, the internal thermal protection circuit shuts down the device and then automatically attempts to re-supply the load until the fault condition is removed.
Unlike mechanical fuses, which must be physically replaced after a single event, the E-fuse does not degrade in its performance after short-circuit/thermal protection interventions.