MLCC (Multilayer Ceramic Chip Capacitor) has now become one of the most commonly used components of electronic circuits. MLCC seems to be, on the surface, very simple, but, in many cases, the design engineers or production, process personnel on the understanding of the MLCC but there is a lack of place. The following talk about MLCC selection and application of some of the issues and considerations.
1, MLCC is relatively simple, but, is also a relatively high failure rate of a device. Failure rate is high, on the one hand, the MLCC structure of the inherent reliability problems, in addition to selection issues and application issues.
Because capacitors are considered "simple" devices, some design engineers do not pay enough attention to them and thus do not understand the unique characteristics of MLCCs. In an idealized situation, when selecting capacitors, the main consideration is the capacity and withstand voltage two parameters are enough. However, for MLCCs, it is not enough to consider only these two parameters.
2, for the entry soon design engineers, the component specifications of the number of sequences (E12, E24, etc.) do not have a concept, will be given to the 0.5uF and other non-existent specifications out. Even experienced engineers have no idea about the compression of specifications. For example, in the filter circuit, the original someone used a 3.3uF capacitor, his circuit can also be used 3.3uF capacitor, but he may choose a 4.7uF or 2.2uF capacitor specifications have not been used. Do not look at the manufacturer's selection manual selection of people, but also make the following mistakes, such as selecting a 0603/X7R/470pF/16V capacitors, and in fact the general manufacturers 0603/X7R/470pF capacitors are only produced in the 50V and above the voltage and not 16V and other voltages.
3, in addition to note that the chip capacitor package there are two ways of expression, one is the British system of expression, a metric system of expression. U.S. manufacturers with imperial, Japanese manufacturers basically metric, and domestic manufacturers with imperial and metric. A company used to the capacitor package, can only be unified with a system to indicate that the engineers can not use this engineer with the British system that engineer with the metric system. Otherwise it will get confused
4, in addition, design engineers in addition to understanding the temperature performance of the MLCC, but also should know more about the performance. For example, Y5V dielectric capacitors, although the capacity is very large, however, this ferroelectric ceramics have a disadvantage, in that its static capacity with its DC bias voltage increases and decreases, the maximum will even fall 70%. For example, a Y5V/50V/10uF capacitor, in the 50V DC voltage, its capacity may be only 3uF!
5, different materials have different frequency characteristics. Designers must understand the different frequency characteristics of different materials. For example, C0G (also known as high-frequency thermal compensation dielectric) of the high-frequency characteristics of good, X7R second, Y5V poor. In the smoothing (power supply filtering) purposes, the requirements of the capacity as large as possible, so available Y5V capacitors, that is, Y5V capacitors can replace the electrolytic capacitors.
6, generally speaking, MLCC ESL (equivalent series inductance), ESR (equivalent series resistance) is small, is relative to the electrolytic capacitors (including tantalum electrolytic capacitors). In fact, at high frequencies, the ESL and ESR of MLCCs are not negligible. General C0G capacitor resonance point can reach hundreds of MHz, general X7R capacitor resonance point can reach dozens of MHz, while the Y5V capacitor resonance point is only a few MHz or even less than 1MHz. The resonance point means that, beyond this frequency, capacitance is no longer a capacitive characteristic, but an inductive characteristic. If you want to use MLCCs for higher frequencies, such as microwave, then you must use specialized microwave materials and processes to manufacture MLCCs. Microwave capacitance requires that the ESL and ESR must be much smaller.