March 2012

Doc ID 022926 Rev 1

1/16

AN4069

Application note

5 V and 12 V power line protection based on STEF05 and STEF12

electronic fuses

Introduction

This demonstration board is based on the STEF05 and STEF12 electronic fuses (E-fuses).

It is designed to help developers to evaluate the benefit of the complete protection offered by

the E-fuse family and to customize their own application. The E-fuse family of hot-swap

converters is designed to replace the mechanical fuses on low voltage power lines.

The STEF05 and STEF12 are integrated electronic fuses optimized for monitoring the

output current and input voltage. Connected in series to the 5 V/12 V rails, they are capable

of protecting the electronic circuitry on their output from overcurrent and overvoltage.

The turn-on time is programmable by means of an external capacitor, allowing the control of

the inrush current at startup and during hot-swaps.

When an overload condition occurs, the E-fuse 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, when

power is re-applied the E-fuse initially limits the output current to a safe value, and then

again goes into an open state. Both devices are equipped with a thermal protection circuit.

The intervention of thermal protection is signaled to the board monitoring circuits through a

signal on the ENABLE/FAULT pin that can be connected to other parts belonging to the

same family to cause a simultaneous shutdown during failure events.

Unlike mechanical fuses, which must be physically replaced after a single event, E-fuses do

not degrade in their performance after short-circuit/thermal protection interventions and can

be reset either by re-cycling the supply voltage or by using the ENABLE pin.

Figure 1.

Board image

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