Alternative Component (Second Source)
An alternative component is an electrically and mechanically equivalent replacement part that can be used without changing the board design when the main part cannot be sourced. Equivalence is not just package compatibility; threshold voltage, on-resistance, speed and temperature behaviour must also be compared.
For a part to count as an alternative, compatibility is required at three levels.
- Mechanical compatibility: same package, same pad layout, same pin order. An IC that performs the same function but has a different pin order is not an alternative, it is a reason for a revision.
- Electrical compatibility: for a power MOSFET the on-resistance and gate threshold voltage, for a regulator the dropout voltage, for an optocoupler the current transfer ratio are compared. A MOSFET with a high gate threshold may not turn fully on with the same driver stage and will heat up more.
- Behavioural compatibility: switching speed and the variation curve with temperature. A much faster part can generate extra noise in the same circuit.
Alternatives are identified on paper, verified on a few boards and then recorded in the bill of materials as an "approved second source". Using an unverified equivalent in a rushed production run is a common source of problems that only show up in the field months later.
The context in which this term is used: Our Services