eFuses bring intelligence to power protection

Fuses have existed since the discovery of electricity, providing a way to disconnect a load during overcurrent conditions. These simple devices were low cost, simple to use and reliable. However, they lacked flexibility and required physical replacement after they had operated, which could be highly inconvenient depending upon the location of the equipment they were deployed in.

Conventional fuses are sacrificial devices that contain a thin wire that melts during overcurrent conditions, thereby disconnecting the load. This prevents damage to power sources and loads, eliminating any risk of overheating or fire as well as safeguarding users from a potential electric shock due to the fault.

In systems that are located nearby and not sealed, conventional fuses are often adequate, however there are significant limitations – especially in more complex systems.

Firstly, the time taken to ‘blow’ depends upon the current applied and there may be a significant delay before disconnection, permitting damage to occur. This is further compounded by the wide (+/-25%) tolerance of these devices.

Complex systems, such as those containing inductive or capacitive elements can experience large inrush currents on startup which is particularly challenging in the context of conventional fuses.

Fuse technology has advanced to include resettable devices such as polymeric positive temperature coefficient (PPTC) devices. PPTCs increase resistance as they heat due to an overcurrent and return to normal as the heat subsides. This can be useful in interfaces (such as USB) but PPTCs remain slow to react, they do not disconnect the load completely and they are affected by ambient temperature.

Increasingly, sophisticated modern electronic systems require more advanced protection that is able to deal with a variety of situations while providing comprehensive protection that is fast acting. eFuses were invented to address this need.

eFuse devices are based upon a MOSFET that is controlled by an integrated current-sensing circuit. Should the current exceed a definable threshold, the MOSFET opens rapidly (<1uS), preventing damage to the system. As solid-state devices, eFuses are resettable, either automatically or via a signal from a microcontroller, enabling rapid recovery and reducing downtime.