Due to the integration of the 48 V electrical system and the 48 V standard in mild hybrids, protection against overcurrents or short circuits also needs to be reassessed, since a greater distance is required between the relay contacts at 48 V (supply voltage) than at 12 V in order to extinguish the arc that occurs when the protective relay is switched. This results in a delayed shutdown and faster wear of the contacts.
Therefore, conventional 48 V relays are replaced with eFuses. They are based on semiconductors and do not have contacts whose wear is fundamentally linked to switching devices. This leads to a longer service life. Furthermore, their faster switching behavior, diagnostic capabilities, and lower tolerances ensure significantly greater safety.
Vishay has developed a smart eFuse that is designed to continuously switch loads up to 200 A at 48 V. The maximum current can be set between 1 and 200 A. If the set value is exceeded, the eFuse switches within 1 µs. In contrast to a conventional fuse, the eFuse can be reset, meaning it does not need to be replaced after tripping.
Even at a switching capacity of 200 A, its power loss does not exceed 14 W. In other words, passive cooling is sufficient up to an ambient temperature of 100 °C. Active cooling is only required at higher ambient temperatures.
Two-stage switch-on behavior
The smart eFuse operates with a two-stage switch-on procedure. The short-circuit test is performed first. During the test, a 13 µs pulse is applied via a resistor connected in series. If the output voltage is below 10% of the input voltage, a short circuit is assumed and the eFuse switches off again. However, if the output voltage is above 10% of the input voltage, the second stage, also known as pre-charging, takes place.
To prevent excessive current caused by capacitive components on the consumer side when the eFuse is switched on, the components are pre-charged via a series resistor until the output voltage corresponds to 85% of the input voltage. Upon reaching this value, the eFuse is switched on.
Main components of the smart eFuse
At the core of the smart eFuse are 20 N-channel SQJQ160E MOSFETs from Vishay. They are based on the latest TrenchFET Gen-IV technology, which enables a very low RDSon of just 0.8 mΩ. As bidirectional MOSFETs, they prevent reverse-current flow when the eFuse is switched off. They come in a compact PowerPAK-8x8L package and operate reliably within a –55 °C to +175 °C temperature range.
Very low power loss is guaranteed by the high number of MOSFETs connected in parallel with a total RDSon of 0.3 mΩ. The temperature of the MOSFETs does not rise to more than 65 °C above the ambient temperature.
The WSLP3921L3000FEA shunt from Vishay allows accurate current measurement with minimal power loss, ensuring safe fuse shutdown. Its AEC-Q200 certification and 1% accuracy at 0.0003 Ω resistance make WSLP3921L3000FEA ideal for safety-related applications.
Temperature monitoring of the board also contributes to an increased level of safety. It is implemented with Vishay’s NTC thermistor NTCS0805E3103JMT. It, too, is AEC-Q 200 certified and has 10 kΩ resistance with a deviation tolerance of 5%.
The components are located on a double-sided FR4 (flame-retardant) board measuring 125 mm × 60 mm in size. The smart eFuse can be controlled both via control elements on the board and via an external microcontroller or mechanical switch. The board’s power consumption is 53 mA when the eFuse is disabled and 95 mA when it is conductive.
With these features, the smart eFuse from Vishay enables modern circuitry concepts and thus paves the way for the development of future-oriented vehicles.
For more information and a direct ordering option, please visit our e-commerce platform at www.rutronik24.com.
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