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  • LIN Transceiver with Reverse Battery Protection

  • Created: Jun 18, 2014

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Summary

A common requirement for most battery-powered applications is a reverse-battery-protection safeguard. This safeguard can be either mechanical or electronic, and there is often a special connector or symbol to highlight it in the application circuit. Electronic battery-reverse-voltage protection is preferred, however, because it provides a higher level of safety. The simplest form of battery-reversal protection is a diode in series with the positive supply line. The diode allows current from a correctly installed battery to flow to the load and blocks current flow to a backward-installed battery. This solution has two major drawbacks: The diode must handle the full load current, and its forward voltage drop shortens the equipment's operating time (the regulator output is one diode drop below the battery voltage, so the regulator drops out prematurely).

The TJA1021 is the interface between the Local Interconnect Network (LIN) master/slave protocol controller and the physical bus in a LIN. It is primarily intended for in-vehicle sub-networks using baud rates from 1 kBd up to 20 kBd and is LIN 2.1/SAE J2602 compliant. The TJA1021 is pin-to-pin compatible with the TJA1020 with an improved Electrostatic Discharge (ESD) specification. The transmit data stream of the protocol controller at the transmit data input (TXD) is converted by the TJA1021 into a bus signal with optimized slew rate and wave shaping to minimize Electromagnetic Emission (EME). The LIN bus output pin is pulled HIGH via an internal termination resistor. For a master application, an external resistor in series with a diode should be connected between pin INH or pin VBAT and pin LIN. The receiver detects the data stream at the LIN bus input pin and transfers it via pin RXD to the microcontroller.

After changing the battery of a car or during maintenance work on the electronic system of a car, the battery has to be reconnected. During this event, it is possible that the polarity of the battery could be applied in reversal direction. Today’s battery terminals are marked with colors and the terminal post itself are mechanically different, nevertheless the possibility for reverse battery is still present, at least for short connection duration. With reverse applied voltage, shorts via diodes or transistors could occur leading to fatal errors of the electronics of the car. This means, that the ECUs (Electronic Control Unit) have to be protected against reversal battery polarity.

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