Select Schottky diodes based on avalanche performance

February 06, 2012 // By Helene Goulin and Philippe Merceron
Helene Goulin and Philippe Merceron, STMicroelectronics examines how to select the best Schottky diode in automotive applications to preserve the low forward voltage drop performance on one side and the ability to pass the ISO7637-2 pulses.

Automotive electronic modules require reverse battery protection to avoid the risk of destruction following the poor handling of the battery. Schottky diodes are preferred in this application because of their low forward voltage drop performance.

Although they are well suited to fulfill this requirement, they have to support the ISO7637-2 pulses, thus they are quite often chosen with a high breakdown voltage to pass the negative Pulse 1 and Pulse 3a tests—which does not help in getting the best forward performances because of the Schottky intrinsic trade-off obeys the rule: Higher the breakdown voltage, higher the forward voltage drop.

However there is a possibility to conciliate both conditions. Indeed, Schottky diodes have the ability to dissipate some power in the reverse condition—which deals with PARM parameter (repetitive peak avalanche power). For instance a 100V breakdown voltage Schottky diode may support on one hand the negative Pulse 1 and Pulse 3a of the ISO7637-2 standard and on the other hand offers a very good performance in forward due to very low voltage drop.

This article explains how to choose the best Schottky diode in automotive applications in order to preserve the low forward voltage drop performance on one side and the ability to pass the ISO7637-2 pulses.

State of the art
ISO16750 standard recognizes that automotive power rails may be subjected to some variations. Reverse battery connection due to poor maintenance is described as a big risk and electronic module suppliers know that some care shall be taken to handle this problem. Thus they add a battery reverse protection device to make their module survive.

Most of the time the reverse battery protection solution consists in adding a diode in series that prevents negative current to flow as the battery connection is reversed (Figure 1).

Figure 1: Typical schematic of a powered automotive module using a Schottky diode as reverse battery protection.

One of the drawbacks of this solution is that

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