AN3361 Datasheet - STMicroelectronics

Introduction
Electronic modules connected to automotive power rails may be affected by polarity inversion due to poor battery handling and load-dump surges when the battery is disconnected while the alternator is still charging. To protect against these phenomena, module manufacturers add reverse-battery protection, usually using diodes.

Schottky diodes are preferred over bipolar ones because of their higher performance in direct conduction. Schottky diodes feature a low forward voltage drop, and are able to withstand the pulses defined in ISO 7637-2.

However, the diode needs a breakdown voltage higher than 150 V in order to pass the tests for negative pulses 1 and 3a, whereas this tends to lower the forward performances. For Schottky diodes, the intrinsic trade-off obeys the rule: the higher the breakdown voltage, the higher the forward voltage drop.

There is a way to reconcile these conditions. Some Schottky diodes (depends on the technology) have the ability to dissipate some power in reverse condition. This concerns the PARM parameter (Repetitive Peak Avalanche Power). For instance a 100 V breakdown voltage Schottky diode may on the one hand support the negative pulse 1 and pulse 3a of the ISO 7637-2 standard and on the other hand offer a very good performance in forward voltage drop.

This Application note explains how to choose the best Schottky diode trade off in automotive applications in order to preserve the low forward voltage drop performance and the ability to pass the ISO 7637-2 pulses.