Melting fuses have two main features. They do not require an auxiliary power supply and, therefore, do not consume power themselves, thus preventing the battery from slowly draining while the vehicle is parked. And if chosen correctly, they protect the power lines in the wiring harness due to their I²t characteristic as the weakest link in the wiring chain. However, as automated driving functions advance, the demands on the 12 V electrical system are forever increasing, making traditional melting fuses inadequate.
In a highly automated vehicle (ADAS level L2 and higher), a short circuit in one part of the electrical system must not affect critical components in other areas or the redundant electrical system. Such faults need to be detected and isolated immediately in order to protect other consumers and the voltage source.
An eFuse must therefore offer additional performance features, such as:
- adjustable triggering characteristic, adapted to the load and the line cross-section,
- low dispersion of the triggering characteristic,
- fast activation in µs,
- resetability via electrical signals or bus communication,
- diagnosis feedback,
- suitability even with capacitive load-switching, and
- support of developments according to ISO 26262 in terms of functional safety.
eFuses with new functions
The new PROFET (Protected Field Effect Transistor) Wire Guard family from Infineon offers a range of new features: The integrated and adjustable I²t function protects wires from overheating. Six I²t protection curves can be selected via an external resistor depending on the cross-section of the connected wire. The temperature model in Wire Guard operates onboard and does not require any assistance from an external microcontroller. This ensures protection even when the µC is in standby mode or going through a reset cycle.
The triggering threshold for fast overcurrent shutdown can also be set via an external resistor. It protects the voltage source (e.g. battery or zone controller) and other consumers from short circuit feedback. Harmful feedback can result in extended periods of undervoltage, causing other control units to undergo an undervoltage reset and become unavailable for the driving function. PROFET Wire Guard supports applications with fail-operational architecture by providing rapid error detection and failure isolation in the event of overcurrent.
The diagnosis feedback of the module allows various status and actual values to be read sequentially via one single pin. The status and actual values include the actual current value, the selected I²t protection curve, the I²t status, and the threshold value for overcurrent shutdown.
At low load currents, PROFET Wire Guard automatically switches from I²t mode to IDLE mode. In IDLE mode, Wire Guard reduces current consumption to around 50 µA with a fully controlled switching transistor and active protection functions. Thanks to the energy-saving IDLE mode, Wire Guard is particularly suitable as an eFuse for system sections and loads that are active during parking.
Thanks to the capacitive load-switching (CLS) mode, Wire Guard is also ideal for fast charging and switching on large capacitive loads. Such a capacitive load can, for example, be the DC link capacitors of a motor inverter. To activate CLS mode, the Wire Guard input is controlled with a defined PWM signal. This PWM signal sets the module to CLS mode with the “continuous auto restart” switch-off strategy. The switching cycles “switch on and supply with defined maximum current” and “switch off due to protection against steep temperature rise” are repeated until the voltage drop at the output transistor, in on-state, falls below a certain value. In this case, the capacitive load is considered sufficiently charged. After that, the PWM signal is permanently switched through and can be replaced by a high level at the control input. Advantage: The module remains in the specified safe operating area (SOA) during this period.
Extended product family
Infineon has added several derivatives to the PROFET product family. Load Guard without I²t emulation is intended for lower currents up to approx. 5 A. Moreover, when currents reach critical levels for wiring, Wire Guard products come into their own. They are ideal for use in 12 V power distribution and in zone controllers that operate in an ASIL-classified system and ensure a fail operational concept.
Populated evaluation printed circuit boards with Wire Guard or Load Guard are available for test purposes. These daughterboards fit on the PROFET One4All motherboard. Wire Guard can then be configured and tested using a PC GUI (Infineon Smart Power Configuration Switches Wizard) via an interface converter (µIO stick).
Summary
PROFET Wire Guard from Infineon is well on the way to becoming the ideal eFuse. Thanks to its diagnosis and protection properties, low power consumption, and available safety documents, it is ideally suited for use in 12 V power distribution in terms of functional safety. Wire Guard reliably protects the entire circuit consisting of the source, Wire Guard itself, wiring, and load.
For more information and a direct ordering option, please visit our e-commerce platform at www.rutronik24.com.
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