If you take a look at the main board of an electronic device such as a personal computer, you’re likely to see some of the six types of capacitors shown below (Fig. 1). Common types of capacitors include tantalum electrolytic capacitors (MnO2 type and polymer type), aluminum electrolytic capacitors (electrolyte can type, polymer can type, and chip type), and MLCC.
Figure 1. Main Types of Capacitors
What is a Polymer Capacitor?
There are many other types of capacitors, such as film capacitors and niobium capacitors, but here we will describe polymer capacitors, a type of capacitor produced by Murata among others.
In both tantalum electrolytic capacitors and aluminum electrolytic capacitors, a polymer capacitor is a type of electrolytic capacitor in which a conductive polymer is used as the cathode. In a polymer-type aluminum electrolytic capacitor, the anode is made of aluminum foil and the cathode is made of a conductive polymer. In a polymer-type tantalum electrolytic capacitor, the anode is made of the metal tantalum and the cathode is made of a conductive polymer. Figure 2 shows an example of this structure.
Figure 2. Example of Structure of Conductive Polymer Aluminum Capacitor
In conventional electrolytic capacitors, an electrolyte (electrolytic solution) or manganese dioxide (MnO2) was used as the cathode. Using a conductive polymer instead provides many advantages, making it possible to achieve a lower equivalent series resistance (ESR), more stable thermal characteristics, improved safety, and longer service life. As can be seen in Fig. 1, polymer capacitors have lower ESR than conventional electrolytic capacitors.
Note that the type of valve metal used for the anode basically determines the type of dielectric, and this in turn determines the dielectric constant and DC bias characteristics, as well as the acoustic noise characteristics. Thus, a wide variety of characteristics can be obtained by combining anodes, cathodes, and dielectrics made of different materials. Each has its own strong and weak points, and these must be kept in mind when selecting components as part of the circuit design process.
The ECAS Series
Aluminum electrolytic capacitors can be broadly divided into three types, based on the cathode material and the structure. Murata’s aluminum capacitors are all-solid multilayer polymer aluminum capacitors (the ECAS series)(Fig. 3). Other varieties of aluminum capacitors include can-type wrapped aluminum capacitors that use either an electrolyte or a polymer as the cathode. What sets ECAS series capacitors apart are the high conductivity of the conductive polymer used as the cathode and the multilayer (laminated) structure of the aluminum elements. These make possible the lowest ESR obtainable among electrolytic capacitors. ECAS series capacitors also achieve large capacitances, and the capacitance remains stable when DC voltage is applied due to the lack of DC bias. Thus, the major features of the ECAS series are low ESR, high capacitance, and stable capacitance.
Figure 3. Example of Structure of ECAS Series Capacitor
Figure 4. ECAS Series Capacitor lineup
Comparison of Capacitor Characteristics
We will compare the characteristics of different types of capacitors, bringing in related data where relevant.
Figure 5 is a comparative table of capacitor characteristics. Aluminum electrolytic capacitors (can type) using a conventional electrolyte and tantalum electrolytic capacitors using manganese dioxide (MnO2) are comparatively inexpensive, but they are inferior to polymer capacitors in their frequency characteristics, temperature characteristics, service life, and reliability. Murata’s ECAS series multilayer polymer aluminum capacitors have a relatively smaller lineup of product versions than other polymer capacitors, but their frequency characteristics, in particular, are superior.
(symbol) ◎: excellent, ○: good, △: normal, ◎: bad
Figure 5. Comparison of Capacitor Characteristics
Figure 6. Comparison of ESR and Capacitance @each Al capacitor (2V/330uF)
Main Applications of the ECAS Series
By adding the ECAS series to its line of multilayer ceramic capacitor (MLCC) products, Murata has further broadened the range of options available to customers. As electronic devices gain ever-more-sophisticated functionality, stricter voltage control is needed for the power lines of the CPU, etc. Maintaining voltage line stability sometimes requires large capacitance. In the past we would have suggested using multiple MLCCs, but now in many cases we can propose combining ECAS series capacitors with MLCCs in order to reduce both the quantity and cost of components.
Figure 7. Simplified Circuit Diagram of Power Line for CPU or FPGA
The ECAS series delivers low ESR, low impedance, and stable capacitance, making it ideal for applications such as smoothing (eliminating ripple and high transient response) various types of power lines subject to large fluctuations in the current load.
Basically, ECAS series capacitors are almost always used in combination with MLCCs, and the ECAS series capacitors really show their value in applications involving suppression of voltage fluctuations (high-speed back-up). Polymer-type tantalum electrolytic capacitors and polymer-type aluminum electrolytic capacitors (can-type) are widely used to suppress voltage fluctuations, but ECAS series capacitors are even more ideally suited for such applications due to their low ESR and good balance between ESR and capacitance.
If you are designing the power line for a CPU, we recommend the ECAS series.
Comparison of Application Performance
1. Good ripple absorption performance
Comparing voltage smoothing performance at the switching power output side with other capacitor types.
Figure 8. Good ripple absorption performance (2V/330uF)
2. Good transient response performance
Comparing transient response characteristics during quick load change with other capacitors.
Figure 9. Good transient response performance (2V/330uF)
Main Markets of the ECAS Series
The ECAS series capacitors are widely used in products such as consumer applications (notebook PCs, LCD televisions, game consoles, set-top boxes,etc.), Enterprise ones, Industrial ones and Network ones.
Figure 10. Main Markets of the ECAS Series
The comparison of characteristics outlined above is only partial in nature. Each type of capacitor is well suited to some fields and poorly suited to others. When actually designing circuits it is necessary to consider a number of factors in addition to the characteristics described above, such as cost and size, in order to select the best capacitor for the job. Typical aluminum electrolytic capacitors can be said to be suitable in cases where there are no space constraints and large capacitance is the only relevant characteristic, whereas polymer capacitors are a good choice when both capacitance and ESR are important. If space is limited, all-purpose MLCCs are best. MLCCs are also suitable for applications where the ability to deal with very high voltages is needed because of their high withstand voltage performance and ability to withstand reverse voltage.
ECAS series capacitors combine low ESR and comparatively high, stable capacitance, so they are particularly well suited for current smoothing and improving transient response characteristics in power lines subject to sudden load fluctuations, such as CPU or FPGA power lines. And since they have a lower profile than can type aluminum electrolytic capacitors, ECAS series capacitors are suitable for use in electronic devices where thinness is required. Their stable capacitance temperature characteristics mean that they can also be employed in electronic devices intended for use outdoors.
Figure 11 is a summary view that shows a motherboard as viewed from the side. Passive components of the sort shown here are typically arranged around the active components such as the CPU and DC-DC converter. Basically, it is necessary that the target impedance is met in order to ensure that electronic devices operate properly. A variety of capacitors of different types are arranged in combination to achieve this.
Figure 11. Example Uses for Each Capacitor Type
Refer to the following webpage for details of the ECAS series lineup:
Produced by: Polymer Device Department, Murata Manufacturing Co., Ltd.