This application note explains how to choose the best Schottky diode for automotive applications. It explains the trade-off between the forward voltage drop and the breakdown voltage, and provides the test methods for the reverse avalanche performance of Schottky diodes.
Electronic modules connected to automotive power rails may be affected by polarity inversion due to poor battery handling and load-dump surges. 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, featuring a low forward voltage drop.
However, the diode needs a breakdown voltage higher than 150 V to pass tests for negative pulses defined in ISO 7637-2, which tends to lower forward performances. This application note explains how to reconcile these conditions by choosing Schottky diodes that can dissipate some power in reverse condition (Parm parameter) to withstand the required surges while maintaining good forward performance.
Schottky diodes feature a low forward voltage drop compared to conventional bipolar diodes, which reduces power dissipation.
For Schottky diodes, the higher the breakdown voltage required to pass tests, the higher the forward voltage drop.
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.