Overcoming the limitations of traditional protection devices with eFuse

Using e-Fuses to Overcome the Limitations

of Legacy Protection Devices

Overcoming the limitations of traditional protection devices with eFuse

Abstract: Reliability is of paramount importance in modern automotive and industrial applications. Whether the end product is simple or complex, from automotive zone controllers to computer numerical controls in industrial applications, failure to ensure reliability can damage the manufacturer’s reputation. In addition, the cost of warranty repairs or even product recalls must be considered. However, electronic circuits will always fail, either due to external influences or due to component degradation over time. Therefore, good design practice recommends the use of circuit protection devices to ensure that the effects of failures are minimized. This article describes the limitations of standard circuit protection devices and how electronic fuses can be used to improve designs.

The most common (and cheapest) form of circuit protection is the ordinary fuse. This type of fuse is usually based on a metal wire or thin metal strip with a low melting point temperature. The fuse is usually inserted into the power supply line, and when the rated current is exceeded, the heat generated in the fuse causes the metal wire/metal strip to melt, thus disconnecting the circuit from the power supply.

This disconnection is usually not instantaneous, and the time it takes for the fuse to "blow" is inversely proportional to the magnitude of the fault current. If the current is only slightly above the fuse rating, it may continue to pass for a while, affecting the supply rail and causing circuit malfunction or damage.

Fuses are inconvenient to use; once they blow, they need to be replaced (usually by the user). If the user (accidentally or intentionally) uses the wrong rating, they pose a fire risk.

For circuit protection, other devices can be used, such as positive temperature coefficient (PTC) thermistors. These devices mounted on the PCB increase in resistance as temperature rises, limiting the flow of current. As long as the overcurrent is not too large (otherwise the PTC thermistor would become an open circuit), the temperature will drop as the current decreases and normal operation will resume.

While fuse replacement is no longer necessary, PTC thermistors are non-linear and, due to their operating principle, are not suitable for applications over a wide temperature range.

Electronic fuse

Electronic fuses (also known as eFuses, a term coined by ON Semiconductor when it first introduced these devices) are an alternative that provides basic circuit protection functions today, as well as many additional features. Typically, they provide overcurrent (including short circuit), overvoltage, reverse current, and overtemperature protection.

While these innovative devices have many applications, they are often used in hot-swap situations, or where power failures are common, in applications where there is a high probability of load failure, or in systems where inrush current needs to be limited.

The enable pin, combined with a high-precision current control mechanism, allows the device to combine the functionality of a load switch and a fuse, becoming a basic building block for point-of-load control systems in modern power distribution architectures.

The main benefits of eFuse are flexibility and automatic reset capabilities without user intervention. As an intelligent device, these additional features allow eFuse to perform more functions in the system than just overvoltage/overcurrent protection (which eFuse excels at).

For example, many eFuses include a power good (“PGOOD”) pin that can be used with a system controller to precisely sequence power rails. Some eFuses also include a tri-state pin that can be used to ensure that multiple power rails are turned on and off simultaneously.

Electronic fuses are able to detect reverse current flow (which traditional fuses cannot), making them useful in redundant power applications where ORing is required. They are also useful in situations where a bulk capacitor is required to maintain charge after the system has been shut down, typically to limit inrush current at startup.

Figure 1: Electronic fuses offer several features to enhance protection

In many applications, capacitors (or capacitive loads) can present challenges, resulting in large inrush currents that can damage components or PCB traces. Electronic fuses can provide a variety of features to help designers address this issue, such as self-recovery or limiting inrush current to allow capacitors to charge in a controlled manner.

As intelligent devices, e-fuses can monitor temperature, voltage, and current and communicate that data to the system controller. This is particularly useful in detecting early warning signs of failure.

Electronic Fuses in Automotive Applications

As more technology is integrated into cars, the need for circuit protection increases to ensure reliable operation and prevent damage. Circuit protection is especially important in cars because the current capability of the battery is enough to damage delicate electronic components.

Electronic fuses are often used in the power lines of subsystems, such as head-up displays or infotainment systems, in order to disconnect and shut down these systems in the event of a fault.

In some systems located outside the vehicle, damage to external components may cause a short circuit, thereby damaging the internal circuits. For example, in a telematics system, the external LNA and GPS antenna are connected through an electronic fuse to protect the in-vehicle circuits.

If the vehicle system is divided into different zones, electronic fuses can be cascaded within the system to provide overall protection as well as subsystem protection.

Figure 2: Cascaded electronic fuses are sometimes used in automotive zone control applications

For example, in an advanced driver assistance system (ADAS) domain controller, a primary fuse may be connected between the power supply and the main system, while a secondary fuse may be used to protect system peripherals such as an externally mounted ultrasonic parking assist sensor unit.

The wiring harness in a modern car is a complex subsystem. Once the vehicle is assembled, it is costly and difficult to replace the harness, so protection is critical. The harness connects many power-consuming devices (fans, window motors, air conditioning, other actuators). Fuses are usually used before these systems to protect the harness from excessive current.

Examples of the Latest Electronic Fuse Technology

The ON Semiconductor NIV(S)3071 is a 60 VDC, 65 VTR eFuse that integrates four independent channels into a single 5.0 mm x 6.0 mm package, each channel supporting up to 2.5 A of continuous current (10 A total). The RDSon value of only 80 mΩ per channel ensures that energy dissipation within the eFuse is minimized.

All channels have configurable current limit, and other features include output voltage clamping, a digital flag to indicate faults, configurable current trip time, and a fixed 1 ms soft-start.

Capable of operating over a -40ºC to +150ºC junction temperature (TJ) range and offering 2 kV of ESD protection, the NIV3071 is ideal for demanding automotive applications, including 12 V and 48 V.

The NIV(S)4461 is an electronic fuse that provides overcurrent, undervoltage, and inrush current protection in applications such as industrial automation, telecommunications, and computing. The device supports voltages up to 360 V and continuous currents up to 4.2 A.

Notable features of the device include low resistance (typical RDSon = 39 mΩ) and fast trip time. The device also includes programmable current limit (21-157A), undervoltage and adjustable slew rate control. User-configurable features include latch-off and self-recovery.

The NIV(S)4461 is available in a DFNN1024 package measuring only 3.0 mm x 3.0 mm. It has an industry standard pinout and complies with UL2367 and IEC62368 standards.

Summarize

Circuit protection is an essential component of modern design, ensuring circuit and system reliability and minimizing damage in the event of faults or unexpected conditions.

While traditional fuses provide a certain level of protection, modern electronic fuses offer greater precision, flexibility and functionality, significantly improving protection levels.