Robust Automotive Supply Protection for ISO 7637-2 and ISO 16750-2 Compliance: Page 2 of 9

October 22, 2017 //By Dan Eddleman, Linear Technology (Analog Devices)
Robust Automotive Supply Protection for ISO 7637-2 and ISO 16750-2 Compliance
Automotive power supplies produce formidable transients that can readily destroy exposed onboard electronics. Over time, as electronics have proliferated in vehicles, automotive manufacturers have duly noted failures, compiling a rogues’ gallery of the responsible power supply transients. Manufacturers have independently created standards and test procedures in an effort to prevent sensitive electronics from falling prey to these events. Recently, though, automotive manufacturers have combined efforts with the International Organization for Standardization (ISO) to develop the ISO 7637-2 and ISO 16750-2 standards, which describe the possible transients and specify test methods to simulate them.
Figure 2. Unclamped load dump: If the battery connection is lost
during charging, the alternator’s output voltage can surge to 100V.

Without the battery to absorb the stator’s current, the output voltage surges to the very high voltages seen during unclamped load dump, as shown in Figure 3 from the ISO 16750-2 specification. This corresponds to the unclamped alternator scenario in “Test A—without centralized load dump suppression.”

Figure 3. Unclamped load dump pulse shape as described
in ISO 16750-2 specification (“Test A…”)

Alternators with Internal Voltage Clamps

Newer alternators use avalanche diodes that have well specified reverse breakdown voltages which limit the maximum voltage during load dump. Figure 4 shows current flow during a load dump fault in a clamped alternator that uses avalanche rated diodes in the six diode rectifier.

Design category: 

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