Silicon fuses help simplify vehicle wiring harnesses and reduce weight by eliminating user-accessible fuse boxes and its associated cabling and installation. The savings in weight contributes to improving vehicle performance, including extended driving range and reduced CO2 emissions.
Intelligent fuse protection can keep automotive PCB traces, connectors, and wire harnesses from overheating, often with no impact on load transients like inrush currents. Such requirements can guarantee that the insulation of wires and PCBs are subject to a limited temperature and time budget that’s below the reliability specified values.
Not respecting such specified limits can lead to the formation of a conducting path by carbonization across the organic insulation materials and the local hot spot can conduct leading to sparking and fire ignition.
STi2Fuse is a new family of intelligent fuses from STMicroelectronics aimed at replacing standard melting fuses in automotive power-distribution systems. ST’s I2t fuse—I2t stands for ampere squared seconds, also known as the melting point in a fuse—is a defining feature of the STi2Fuse product family. It delivers fast-acting, resettable, and reliable overcurrent protection. The STi2Fuse family consists of two kinds of devices: an integrated solution for low/mid-power ranges and a gate controller for high-power ranges.
STMicro’s proprietary eFuse technology features intelligent circuit breaking aimed at protecting PCB traces, connectors, and wire harnesses from overheating. According to the company, these devices help save component and production costs, while extending electric-vehicle (EV) range and reducing the carbon footprint of vehicles. The monitoring, control, and digital interface capabilities of the devices help automotive systems comply with ISO 26262 and related Safety Integrity Levels (SIL).
Power Protection
The VNF1048F automotive high-side switch controller combines system-protection and diagnostic features with eFuse functionality for the implementation of an overcurrent protection mechanism. The control IC is interfaced to a host microcontroller through a 3.3- and 5-V CMOS-compatible SPI interface and provides protection and diagnostics to the system.
As the first in ST’s new STi2Fuse family with integrated I2t protection, the VNF1048F is compatible with 12-, 24-, and 48-V automotive power subsystems. Its flexibility is well-suited for the latest automotive zonal electronic/electrical architectures that boost efficiency and reliability while supporting increased electrification.
The controller has a serial peripheral interface (SPI) for a host microcontroller to configure and monitor system-protection and diagnostics. These include undervoltage and overtemperature protection, thermal protection for the external high-side MOSFET, desaturation shutdown, and I2t fuse settings. Precision digital current sensing is built-in. Analog-to-digital converters (ADCs) for monitoring the temperature-sensing thermistor voltage, output voltage, and MOSFET drain-source voltage also are integrated in the device.
When the current in the load is pulse-width-modulated, the eFuse function calculates the mean square root of the current. Mean square root of the current also is calculated when switching the power switch on/off during normal operation or after a switch is turned off due to a short-circuit/overload condition. So, if, for example, the circuit is broken due to an overload and after a while the circuit is activated again, the eFuse keeps the previous condition in memory.
The VNF1048FTR is in production now and available in the QFN 32L 5- × 5-mm, 32-lead package from $1.77 for orders of 1,000 pieces.