June Birth Magoncia

user Electronics Engineer

city Innovuze Solutions, Inc.

  • Automotive Precision eFuse

  • Created: May 09, 2017

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In different applications like in automotive, fuses are used to avoid damages caused by current surges or overcurrent. However, traditional fuses used in the automotive field are low in accuracy and response time. This slow response time creates damage possibilities to loads and series path components such as wiring, semiconductors, and connectors. In this reference design, an automotive efuse is designed to replace a traditional fuse. This efuse offers overcurrent protection with higher accuracy and features not found in traditional fuses.

This automotive efuse is built out of semiconductor devices. The circuit design can be categorized into the following sub-circuits: (1) current sense and activation (CSA), (2) switch and control (SC), and (3) LDO power supply and protection (transient suppression). The efuse is bidirectional, which means that either J1 or J3 can be connected to the battery while the other one is connected to the load. Both terminal lugs (J1 and J3) have TVS diodes (D1 and D3) connected in parallel to the input which act as transient suppressors. The CSA circuit is mainly composed of current sense resistors in parallel (R1 and R3) and two INA300 current sense comparator configured for bidirectional operation. The role of the CSA circuit is to monitor the current flowing from the battery to the load and provide activation signal to the SC circuit. When current flows through the current sense resistors (R1 and R3), there is a voltage dropped across the differential inputs of the INA300 device. This voltage serves as a reference whether the current flowing from the battery to load is normal or excessive. If the current is normal, the /ALERT pin of the INA300 pulls the gate of Q4 HIGH which allows Q1 and Q2 to conduct so that current can flow from the battery to the load. But if overcurrent condition occurs, the /ALERT pin is pulled LOW and as a result, both Q1 and Q2 turns OFF, disconnecting the load from the battery to avoid damage. The SC circuit as shown in the schematic diagram, is composed of Q1, Q2, Q3, Q4, and some protection diodes. Q1 and Q2 are used for switch and reverse polarity functions while Q3 is used to switch and discharge the gate to source voltage of Q1 and Q2. The MOSFET Q4 receives the activation signal from the CSA circuit and is used to turn off the switch circuit. R4, R11, and R13 are used to bias the circuit during the startup and operation phases. D4 is used to protect Q3 while D2 and D9 are used to protect Q1 and Q2, respectively. The power supply is mainly composed of a wide input voltage LDO regulator LM9036 and switching diodes from the DB3X316N0L device. The DB3X316N0L internal diodes serve as current steering diodes which allow power supply input to the LM9036 either from J1 or J3 terminals. The LM9036 generates 3.3V to supply the INA300 devices.

The design of this automotive efuse allows DC input operating voltage from -28V up to 28V. The overcurrent limit is up to 30A with an accuracy of 97.36%. The average turn on resistance of this efuse design is 11.05mΩ. The trip current response time is 13.8us. This efuse can be used in applications such as automotive efuse box, body control module, high-side smart switch, and electronic control unit.