Definition of the electrical transients and tests

AN3361

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Definition of the electrical transients and tests

Two ISO standards are applicable to this situation.

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ISO 16750

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ISO 7637-2

The ISO 16750 standard defines the variations that automotive power rails may undergo. A

reverse battery connection due to poor maintenance is described as a key condition to be

considered. Electronic modules thus usually have a reverse battery protection device to

guard against this condition. Most of the time this protection consists of a diode in series

that prevents negative current from flowing if the battery connection is reversed (see

Figure 1).

This solution involves a voltage drop across the diode and therefore some power

dissipation. This is why a Schottky diode is preferred as its forward voltage drop is less than

that of a conventional bipolar diode.

Figure 1.

typical schematic of a powered automotive module using a Schottky

diode as reverse battery protection

ISO 7637-2 specifies the methods and procedures to test for compatibility with conducted

electrical transients of equipment installed on passenger cars and commercial vehicles fitted

with 12 V or 24 V electrical systems, whatever the propulsion system (spark ignition or

diesel engine, electric motor). The standard describes bench tests for both the injection and

measurement of transients.

The bench tests consist in applying positive or negative pulses to the modules. The test is

successful if there is no damage on the device. Each pulse models an abnormal behavior.

The most sever cases are given in Table 1.

Battery reverse protection

Electronic module

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