AN2689 datasheet(6/42 Pages) STMICROELECTRONICS

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Electrical hazards in the automotive environment

AN2689

6/42

Doc ID 14310 Rev 3

The ISO 10605 ESD surge test is applied to a complete system. This is simulating the ESD

occurring on an electronic module in its environment due to human body contact.

1.2.2

Hazards on the supply rail

Transients that are generated on the supply rail range from severe low level-high energy, to

high level-low energy with sometimes high dv/dt. These mainly concern ISO 7637-2 and

ISO 10605 standards.

Figure 4 shows a simple representation of the form of major supply rail transients.

Figure 4.

Kinds of surges on power rail

The most energetic transients are those resulting from load-dump and jump start. But all

other hazards may affect the normal operation of electronic modules.

The “6 V crank” is caused by the starting of the car. The energy necessary to crank the

engine makes the power voltage drop to 6 V.

The load-dump is caused by the discharged battery being disconnected from the alternator

while the alternator is generating charging current. This transient can last 400 ms and the

equivalent generator internal resistance is specified as 0.5

minimum to 4  maximum.

The “+150/-220 V Spikes” are due to the ignition system that is necessary to ignite the

gasoline mixture. The frequency of the spikes depends on the engine rotation speed and the

number of cylinders. These generate electromagnetic radiation.

The “24 V jump start” results from the temporary application of an over voltage in excess of

the battery voltage. The circuit power supply may be subjected to a temporary over voltage

condition due to the regulator failing or deliberately generated when it is necessary to boost

start the car. In such condition some repair vehicles use 24 V battery jump to start the car.

Automotive specifications call for the support of this over voltage application for up to 60

seconds.

The “reverse battery” is the result of battery inversion by mistake. Thus accessories have

their power termination polarized in the wrong way.

The “25 kV ESD spike” is the result of electrostatic discharge (ESD)

All these events may affect the electronic environment as conducted hazards or as radiated

hazards.

Nominal

14 V

6 V Crank

87 V

Load dump

50 -220 V

Spikes

24 V Jump start

Reverse battery

±25 kV

ESD spikes

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