In modern automotive and industrial applications, reliability is paramount. From automotive domain controllers to CNC machines in industrial settings, the reputation of manufacturers hinges on ensuring reliability, regardless of whether the final product is simple or complex. Additionally, the cost of warranty repairs and even product recalls must be considered. However, electronic circuits will inevitably fail, either due to external influences or component degradation over time. To minimize the impact of such failures, it is advisable to implement circuit protection devices based on sound design practices. This article explores the limitations of standard circuit protection devices and how electronic fuses can enhance design reliability.
The most common (and cost-effective) form of circuit protection is the traditional fuse. These fuses typically consist of a wire or thin metal strip with a low melting point. When inserted into a power supply line, the heat generated by a current exceeding the fuse's rating causes the wire/strip to melt, disconnecting the circuit from the power source.
This disconnection is not usually instantaneous—the. The time it takes for a fuse to "blow" is inversely proportional to the magnitude of the fault current. If the current is only slightly above the fuse's rating, it may continue to flow for a while, affecting the power supply rail and potentially damaging the circuit.
Fuses are not user-friendly; once blown, they must be replaced, often requiring user intervention. If the user (intentionally or accidentally) uses an incorrectly rated fuse, it can pose a fire hazard.
Other devices, such as Positive Temperature Coefficient (PTC) thermistors, can also be used for circuit protection. These PCB-mounted devices increase their resistance as temperature rises, thereby limiting current flow. Provided the overcurrent is not too high (or the PTC will become open-circuited), the thermistor will cool down as the current decreases, allowing normal operation to resume.
While fuse replacement is no longer needed, PTC thermistors are non-linear and not suitable for applications with a wide temperature range.
Electronic Fuses
Electronic fuses (also known as eFuses, a term coined by onsemi when they first introduced such devices) are an alternative that offers basic circuit protection along with many additional features. Typically, they provide overcurrent (including short-circuit), overvoltage, reverse current, and overtemperature protection.
Although these innovative devices have many applications, they are commonly used in hot-swap situations or environments where power supply faults frequently occur. They are also ideal for applications with a high likelihood of load faults or systems that need to limit inrush current.
The combination of an enable pin and a precise current control mechanism allows these devices to merge the functions of a load switch and a fuse, making them an essential building block in modern point-of-load control systems within power distribution architectures.
The primary advantage of electronic fuses is their flexibility and auto-reset function, which eliminates the need for user intervention. As intelligent devices, these additional features enable electronic fuses to perform more functions within the system beyond just overvoltage/overcurrent protection (where electronic fuses excel).
For example, many electronic fuses include a "PGOOD" (Power Good) pin that can be used with the system controller to sequence power rails precisely. Some also feature a tri-state pin, which can be used to ensure the simultaneous turn-on and turn-off of multiple power rails.
Electronic fuses can detect reverse current (something traditional fuses cannot do), making them valuable in redundant power supply applications requiring ORing. They are also useful in scenarios where large capacitors need to maintain a charge after the system shuts down, commonly used to limit inrush current at startup.
In many applications, capacitors (or capacitive loads) can pose challenges, leading to large inrush currents that can damage components or PCB traces. Electronic fuses offer multiple features to help designers address this issue, such as self-recovery or current limiting to allow capacitors to charge in a controlled manner.
As intelligent devices, electronic fuses can monitor temperature, voltage, and current and relay data to the system controller. This capability is particularly useful for detecting early warning signs of faults.
Electronic Fuses in Automotive Applications
As more technology is integrated into vehicles, the need for circuit protection has increased to ensure reliable operation and prevent damage. Circuit protection is particularly crucial in automotive applications because the battery's current capacity is sufficient to damage sensitive electronic components.
Electronic fuses are commonly used in the power lines of subsystems such as head-up displays or infotainment systems to disconnect and shut down these systems in the event of a fault.
In systems partially located outside the vehicle, external component damage can lead to short circuits that harm internal circuits. For example, in-car infotainment systems with external LNAs and GPS antennas are connected via electronic fuses to protect the internal circuitry.
If the vehicle's systems are divided into different zones, electronic fuses can be cascaded within the system to provide both overall and subsystem protection.
In Advanced Driver Assistance System (ADAS) domain controllers, for example, a master fuse can be connected between the power supply and the main system, while secondary fuses can protect peripherals like externally mounted ultrasonic parking sensors.
The wiring harness in modern vehicles is a complex subsystem. Once the vehicle is assembled, replacing the harness is costly and challenging, making protection critical. The harness connects many power-hungry devices (fans, window motors, air conditioning, other actuators). Fuses are typically used before these systems to protect the harness from excessive current.
Latest Examples of Electronic Fuse Technology
The onsemi NIV(S)3071 is a 60 VDC, 65 VTR electronic fuse that integrates four independent channels into a single 5.0 mm x 6.0 mm package, with each channel capable of supporting up to 2.5 A of continuous current (10 A total). Each channel's RDSon value is only 80 mΩ, ensuring minimal energy loss within the electronic fuse.
All channels feature configurable current limiting, with additional functions including output voltage clamping, digital fault indication, configurable current trip time, and a fixed 1 ms soft start.
The NIV3071 operates within a junction temperature (TJ) range of -40ºC to +150ºC and provides 2 kV ESD protection, making it ideal for demanding automotive applications, including 12 V and 48 V systems.
The NIV(S)4461 is an electronic fuse that offers overcurrent, undervoltage, and inrush current protection in industrial automation, telecommunications, and computing applications. The device supports voltages up to 360 V and continuous currents up to 4.2 A.
Key features include low resistance (typical RDSon = 39 mΩ) and fast trip time. It also offers programmable current limiting (21-157A), undervoltage, and adjustable slew rate control. User-configurable features include latch-off and auto-retry.
The NIV(S)4461 comes in a DFNN1024 package, measuring just 3.0 mm x 3.0 mm, and uses industry-standard pin layouts, compliant with UL2367 and IEC62368 standards.
Conclusion
Circuit protection is an essential part of modern design, ensuring the reliability of circuits and systems while minimizing damage in the event of faults or unforeseen circumstances.
While traditional fuses offer a degree of protection, modern electronic fuses deliver higher precision, greater flexibility, and a wider range of functions, significantly enhancing protection capabilities.
