The engineer’s guide to ceramic capacitors

Do you know the difference between Class 1 and Class 2 ceramics? Do the terms NP0, COG and MLCC mix you up? This guide on when and how to use ceramic capacitors explains it all.

This article is part of The engineer’s complete guide to capacitors. If you’re unsure of what type of capacitor is best for your circuit, read How to choose the right capacitor for any application.

What is a ceramic capacitor?

Ceramic capacitors are used widely. Ceramic capacitors are non-polarized and have a good frequency response because they offer a low equivalent series resistance (ESR) and a low equivalent series inductance (ESL). Small capacitance values can withstand voltages as large as 1 kV. Depending on temperature range, temperature drift and tolerance, ceramic capacitors have two active classes: Class 1 and Class 2.

A ceramic disc capacitor. (Image: Wikimedia / Elcap.)

Ceramic capacitors are available in disc packages with radial leads. Surface mount multilayer ceramic chip (MLCC) capacitors are very popular. The stacking of very thin layers permits MLCC capacitors to provide relatively large values of capacitance at lower voltages. For example, AVX offers a military CDR 25 style MLCC that can possess 0.470 µF maximum at 50 V or a maximum of 0.150 µF at 100 V. Bare leadless disc ceramic capacitors are available for microwave applications.

Illustration of a multilayer ceramic chip (MLCC) capacitor. (Image: Wikimedia / Elcap.)

Class 1 ceramic capacitors

Class 1 ceramic capacitors are accurate and provide temperature compensation inherently. They are the most stable in terms of temperature sensitivity and drift, and they have the lowest losses. Class 1 ceramic capacitors are well suited for resonant circuit applications where stability is critical or where a well-defined temperature coefficient is needed. Consequently, they are used in applications that require a measure of precision, like timers and oscillators. Temperature coefficients are expressed using notation like the following:

• N200 means a negative temperature coefficient of 200 ppm/^oC
• P100 means a positive temperature coefficient of 100 ppm/^oC
• NP0 means the temperature coefficient is 0 ppm/^oC

The Electronics Industry Alliance (EIA) uses the notation COG instead of NP0. Class 1 ceramic capacitors are NP0.

Class 2 ceramic capacitors

Class 2 ceramic capacitors have improved volumetric efficiency, meaning that larger values of capacitance are available with a relatively smaller physical size. However, their tolerance is wider and they are not as stable as Class 1 ceramic capacitors. The ceramic dielectric is characterized by a non-linear change in capacitance over its temperature range. These capacitors are usually selected for use in less critical coupling, decoupling, and bypass applications. They are very susceptible to aging effects.

Class 2 ceramic capacitors have several dielectric names. The more popular groups are X7R, X6R and X5R.

Class 2 ceramic capacitors exhibit microphony. The dielectric has a piezoelectric characteristic. If the capacitor experiences mechanical vibrations, they can be transformed into electrical signals—like a microphone. The reverse effect can also occur. The varying electric field between the plates will cause them to move like a loudspeaker, and this can generate an audible sound. Sensitive low-level signal processing systems use only Class 1 ceramic capacitors to avoid the microphony effect.

Applications of ceramic capacitors

Class 1 ceramic capacitors perform well in applications that require precision like oscillators, timers and analog-to-digital converters. Class 2 ceramic capacitors are the usual choice for non-critical decoupling, coupling and bypassing applications.

Alternatives to ceramic capacitors

Metallized film capacitors are an alternative to ceramic capacitors. The below table describes the differences between these two options.

*Note that PPS is notation for polyphenylene sulfide (PPS) film capacitors. On a data sheet description, you might see “stacked metallized PPS film chip capacitor” for an SMD package.