Depending on the type of dielectric, the capacitance can become reduced at high temperatures, leading to changes in frequency response. The end result is unpredictable performance of a tuned circuit, such as a filter.

C0G dielectric is a class I material. Dielectrics in this class are temperature compensating, and thus are suited for resonant circuit applications or those that require Q and stability of capacitance characteristics. These include critical timing or tuning circuits, high-current or pulse applications, and circuits where low losses are critical, as well as decoupling, bypass, filtering, transient voltage suppression, blocking, and energy storage.

It is possible to produce C0G capacitors that exhibit no change in capacitance with respect to time and voltage, and capacitance change with reference to ambient temperature as low as ±30 ppm/ºC over a wide temperature range. Such a small change can be considered negligible as far as automotive applications are concerned.

With Class II dielectrics like X7R, on the other hand, high values of capacitance can be achieved within small component dimensions. This is ideal for space-constrained automotive control units. Although there’s a measurable change in capacitance with respect to time and voltage, the change is predictable. Also, with careful attention to component design, the change in capacitance with reference to ambient temperature can be kept within ±15% from –55°C to +125°C.

These characteristics make X7R MLCCs suitable for bypass and decoupling applications, or for circuits such as window comparators, where Q and stability of capacitance characteristics aren’t critical. In applications that require greater temperature stability, buffer circuitry may be used to stabilize system behavior. Alternatively, lookup tables may be implemented in software to adjust critical constants.

For critical applications where reliability and capacitance stability at higher operating temperatures are a concern, there’s a new class of dielectric called Ultra-Stable. Devices already in the market have zero capacitance change with respect to applied, rated dc voltage, and temperature-related change of less than ±15% from –55°C up to 150°C