Chip capacitors
As shown, MLCC (Multi-layer Ceramic Capacitors), the shape is well distinguished.
actual internal structure
The principle of parallel plate capacitors is still used, but this is a laminated structure; the electrolytic capacitor is rolled up cylindrical;
Capacitance:
Stacked capacitance range: 0.00001UF to 100UF; generally it is this large, depending on the design of each manufacturer.
Size/Package:
0402, 0603
, 0805, 1206, 1210, 1810, 1812, 2010, 2512, and 2220 are marked with the size of all chip capacitor packages. For common consumer electronics products, in fact, normal or common packages
The sizes are as follows:
0402, 0603, 0805, 1206, why, for the sake of portability, electronic products are becoming smaller and smaller, and the corresponding PCB board and PCBA board are indeed expensive, so the first few are generally used, The most commonly used ones are 0402, 0603, and 0805, so when choosing, don’t take it for granted and say what kind of package you want. After all, the package and capacitance are stipulated in the capacitor packaging specification (for example, you want
a The capacitor in the 0402 package must be 100uf, which is fantastic for ceramic capacitors).
As shown in the figure below: Indicates the package size, mm corresponding to feet (note the difference between inch and mm)
Note: the difference between 0603inch and 0603mm.
Capacitance Accuracy:
This refers to the error of the capacitance value. Generally, the smaller the capacitance value, the higher the accuracy.
The accuracy of the capacitor, the smaller the capacity, the higher the accuracy. (For example, you require a 10pF capacitor), give you an accuracy of 20%, try it, the 10pF will shrink to 8pF immediately, obviously it will not work. Especially for the load capacitance of the CPU crystal oscillator, high precision is required, otherwise frequency offset problems will occur. (There are also circuit applications related to radio frequency circuits, so I won’t say much here).
The withstand voltage value of the capacitor:
Common withstand voltage values are shown in the figure above, and this withstand voltage value is determined by the manufacturer. Generally, the actual normal withstand voltage value is greater than this value. Just like you add 20V voltage to a 10V withstand voltage capacitor, in fact, the capacitor does not necessarily break down quickly. But for example, if the withstand voltage of the capacitor is 10V, then the actual capacitance of the capacitor is different when working in a circuit of 5V and 7.2V.
Capacitor thickness/height:
Manufacturers may be inconsistent, and the thickness will affect the size of consumer electronics. Just like if you want to make a mobile phone thinner, you can’t use very thick capacitors. Depending on the product type, you can only choose capacitors with thin and small packages.
It is also worth noting that in some product types, the height and arrangement of capacitors sometimes affect the natural convection air path during natural cooling.
Capacitor package leads;
As shown in the picture above, the lead wires of the capacitor package are silver, copper or electroplated, and the cheap and expensive ones can be seen at a glance. But which type depends on the requirements for reliability. This material will affect the parasitic parameters of the capacitor, and the impact is relatively large at high frequencies.
Pay attention to the relationship between packaging withstand voltage and capacity;
This is easy to understand, that is, to increase the capacity, the volume must be large or the distance between the parallel plates of the capacitor must be small; but if the distance is small, the withstand voltage value cannot be very large, because there is a restrictive relationship.
And the actual production process does not allow it. MLCC is pressed layer by layer, and the number of layers accommodated under a certain volume is also certain. If it is too close, the capacity is acceptable, but the withstand voltage value is not enough.
Effect of Temperature on Capacitance
temperature characteristics
According to the standards of the American Electrotechnical Association (EIA), MLCCs of different dielectric materials are divided into two categories according to temperature stability:
Class I ultra-stable level – C0G or NP0 (note that it is zero or not), corresponding to the national standard CC series.
Class II stable grade - X7R or X5R; Class II usable grade dielectric material Y5V, Z5U, corresponding to the national standard CT.
Class I capacitor
1. Monolithic ceramic capacitors with temperature compensation characteristics (dielectric constant is several hundred)
EIA (American Electronics Industries Association) standard uses the code form of "letter + number + letter" to indicate the temperature coefficient of class I ceramics, such as C0G, pay attention The middle is "zero", which is commonly written as COG; NP0 (Negative-Positive-Zero) IEC (International Electrotechnical Commission) standard;
C0G (C indicates that the effective figure of the capacitance temperature coefficient is 0 ppm/℃; 0 indicates that the multiplication factor of the effective figure is -1 (that is, 10 to the power of 0); G indicates that the tolerance with temperature is ±30ppm).
Other combinations are just uncommon, but they can be calculated according to the figure below: Calculated according to the above table
, the final TCC of the C0G capacitor is: 0×(-1)ppm/℃±30ppm/℃. The corresponding temperature coefficient of other Class I ceramics, such as U2J capacitors, is calculated as: -750 ppm/°C±120 ppm/°C.
As shown in the figure above and the characteristics of the material capacitor: stable temperature characteristics, small capacitance, high price, often used in resonant circuits.
Most of this type of capacitor capacity is below 1000pF. The main low power performance index of this type of capacitor is the loss tangent value tanφ (DF value). The accuracy of common capacitors is generally below 10%: NP0 is the
most Commonly used monolithic ceramic capacitors with temperature compensation characteristics, its filling medium is composed of rubidium, samarium and some other rare oxides; when the temperature is from -55°C to 125°C, the capacity change is 0±30ppm/°C, and the electric capacity The variation of capacity with frequency is less than ±0.3ΔC.
So these are commonly used in radio frequency circuits: WIFI modules and peripheral circuits; BT circuit modules and peripheral circuits; GPS modules and peripheral circuits and other RF modulation circuits. Because these modules are more prone to heat, the temperature rises, and the large change in capacity will affect the circuit performance. Therefore, the temperature compensation type capacitor is used. In a certain temperature range, the capacitance value is stable and the electrical performance is basically unchanged.
Class II capacitor
1. Temperature-stable ceramic capacitors (stable grade)
X7R temperature range: -55–125°C
X5R temperature range: -55–85°C
High dielectric constant, relatively high capacity, capacity change is affected by temperature. Commonly used in power supply filtering, etc.;
the difference is mainly in the temperature range and the change characteristics of capacitance with temperature. The table below shows what these codes mean.
Take X7R as an example (X means that the capacitor can work at a minimum of -55°C; 7 means that the capacitor can work at a maximum of +125°C; R means that the capacitance changes with temperature as ±15%)
Similarly, the normal operating temperature range of Y5V is -30°C to +85°C, and the corresponding capacitance change is +22 to -82%; while the normal operating temperature range of Z5U is +10°C to +85°C, the corresponding capacitance change is It is +22～-56%.
The capacitance value is above 1000pF. The main performance of this type of capacitor is the equivalent series resistance ESR at low power consumption. The capacity of X7R capacitors is different under different voltage and frequency conditions. It also changes with time and when the
voltage Changes in its capacity are acceptable under conditions. Its main feature is that the capacitance can be made relatively large under the same volume.
2. General-purpose capacitor with temperature limit (available type)
Y5V
general-purpose capacitor with temperature limit, its capacity can change by 22% to -82% in the range of -30°C to 85°C.
Cheap circuits with low precision, low cost.
The high dielectric constant of Y5V allows the manufacture of capacitors up to 4.7μF in a small physical size .
Z5U
has a capacity variation range of 22% to -56% in the range of 10-85°C.
Large temperature characteristic, large capacity and low cost.
Despite its unstable capacity, it has a wide range of applications due to its small size, low equivalent series inductance (ESL) and equivalent series resistance (ESR), and good frequency response.
The following are several common capacitance value variation curves with temperature:
The capacitors described above are generally recommended to use the temperature range;
Actual Model of Capacitance
Commonly used models
The equivalent series resistance of a capacitor is formed by connecting the lead resistance of the capacitor in series with the equivalent resistance of the two plates of the capacitor. The equivalent series inductance of a capacitor is composed of the capacitor's lead inductance and the equivalent inductance of the two plates of the capacitor in series.
TDK officially has related voltage withstand curves, impedance curves, etc., you can pay attention to them;
https://product.tdk.com/info/en/technicalsupport/seat/download.html
comes with a specification:
http://fenghua .com/pdf/mlcc/MLCC-Y5V.pdf
The information comes from the Internet and is not for commercial use.