Network resistors may be used in a wide variety of applications to increase component density, reduce part count and increase factory throughput. They are regularly used in pull up/pull down resistor and terminating resistor applications with a wide range of variants available from several major manufacturers.
In more specialist applications resistor networks may also be used to solve system design challenges including thermal and reliability issues, resistor and tolerance matching and TCR matching. Often a standard device will not match the specific system requirements and custom resistor networks are the only solution. Examples include networks of various resistor values in the same package, resistors with non-standard tolerances and resistor networks designed to solve specific system capacitance or inductance issues.
When designing a custom resistor network there are several issues to consider including:
Dimensions and connection method.
Surge and transient conditions.
Temperature coefficient of resistance (TCR).
Where several resistors are required on the same substrate it is important to first establish the normal operating power rating of each device and sum these to give the total power rating. This, coupled with the connection details, will give a first indication of the resistor network dimensions.
Based on this information the system designer may decide how the surge or transient conditions can reduce the operational life of the network resistor or cause catastrophic failure. It is important to understand these conditions so the resistors can be designed accordingly. The mass of the network, the geometry of the resistor and the final resistor trim all have an influence on resistor network design and manufacture.
One of the key advantages of custom resistor networks is the ability to combine several resistor values, with various tolerances in the same package but there are limitations. Different resistor values may require the use of different manufacturing materials and require varying amounts of substrate area. Close co-operation between the system designer and the resistor manufacturer is required to agree on the inevitable design compromises.
The system designer must clearly state the expected change in the value of a single resistor in response to a change in temperature (TCR). Perhaps, more important, they must also be able to specify the TCR tracking. That is the expected change in the ratio of two or more resistors in response to a change in temperature. A successful end product requires close co-operation between the system designer and the manufacturer.