Factors contributing to the ΠPlacement factor

The Pi_placement factor contribute to the calculation of the Pi_induced factor. The Pi_placement is one of the factor showing if the component is exposed to over stresses. It is well known that component at interfaces are more subjected to overstress. In the same way, the same component will be more exposed in a power function than in a digital function. The typical example of overstress affecting the interfaces is the unpluging of the equipement while powered.

What are the criteria to choose the Pi_placement ?

First of all, for a rapide study, the same Pi_placement may be given to a complete board. For a more detailled study, it is better to define the placement component by component.

Interface or non interface ?

Of course it depends of the whole system architecture.

An item should be placed in the "interface" category if it is subjected to a stronger exposure to overstress because of its position in the whole system.

You are right that :

- Item between the equipement and external systems are interfaces.

- Item at the interfaces are often (but not necessarily) protection items (transil, tranzorb...), filtering items (filters, coil, capacitors - yes), isolation means (optocouplers, transformers...).

Note that if your electronic board do have such protections, this is becauses external overstresses have been taken into account in the design. A well performed FMECA will probably shows that most failures of this protections are not mission critical. The operationnal reliability is therefore better despite the bigger amount of components.

Low level or power ?

From the FIDES Guide point of view, low level analog function are mainly discrete input/output, measurement, analogic logic and so on.

Power function are especially power supply or power transmission.

At first sight I would place the threshold around a current of 1A.

I hope these explanations will help you.

Lambda