Solution Guides

Vol.1 Features of High voltage MLCCs with C0G Characteristics and Replacement Solutions Overview

A wide variety of capacitors, each with their own special characteristics, are used in electronic devices. Generally speaking, the capacitance and withstand voltage (rated voltage) of capacitors are in a trade-off relationship which is difficult to balance. In MLCC of the same size, when increasing the withstand voltage, the capacitance tends to decrease.
Film capacitors possess a good balance of high withstand voltage and capacitance. Since they also possess outstanding frequency characteristics and temperature characteristics, they are widely used in automotive electronics, industrial equipment, home appliances, etc.
However, in recent years, there have been remarkable increases in withstand voltage and capacitance in MLCCs (multilayer ceramic chip capacitors) for temperature compensation (class 1). In particular, even in fields where film capacitors have traditionally been used, resonance circuits for example, replacement with MLCC is now possible.
TDK has developed high voltage MLCCs with C0G characteristics. Through C0G characteristics, these MLCCs achieve withstand voltage of 1000V at the broadest capacitance range (1nF to 33nF) in the industry.
In this guide, we explain the numerous benefits of replacement while comparing the features of high voltage C0G MLCCs with those of film capacitors.

Table of Contents

• Characteristics of main capacitors
• Reason why C0G MLCCs are used in resonance circuits
• Solutions using leaded MLCCs
• Automotive Grade MLCC (multilayer ceramic chip capacitor) CGA series C0G characteristics

Characteristics of main capacitors

MLCCs are divided into two major categories according to the type of ceramic materials used for their dielectric, namely class 1 (temperature compensating) and class 2 (high dielectric constant).
Class 2 MLCCs have a large capacitance. However, they also have a disadvantage in terms of a large capacitance change caused by temperature. On the other hand, while class 1 MLCCs do not offer as high a capacitance as class 2, they display a smaller capacitance change caused by temperature. They also possess outstanding frequency characteristics and are used in circuits which require high precision.

Figure 1 shows the corresponding regions for rated voltage-capacitance in main capacitors: aluminum electrolytic capacitors, film capacitors, and MLCCs (class 1 and class 2).

In terms of capacitance, class 2 MLCCs achieve a capacitance of more than 100μF, as offered by aluminum electrolytic capacitors. Furthermore, even in the past, class 1 MLCC voltage-capacitance overlapped a portion of film capacitor regions. However, the withstand voltage and capacitance have increased in recent years, and the overlapping regions are increasing rapidly.
Table 1 summarizes a comparison of the characteristics of a film capacitor and MLCCs.

Table 1: Comparison of characteristics in main capacitors

	Film capacitor	MLCC (class 1)	MLCC (class 2)
Large capacitance	◎	△	○
Withstand voltage	◎	○	○
Temperature characteristics	◎	◎	△
Frequency characteristics	○	◎	◎
ESL characteristics	○	◎	△
DC Bias characteristics	◎	◎	◎
Moisture resistance	○	◎	◎
Lifespan/reliability	◎	◎	◎
Compact size	△	◎	◎

◎: Outstanding　○: Good　△: Fair

The advantage of aluminum electrolytic capacitors is their large capacitance. In terms of other characteristics, film capacitors and MLCCs are superior. Unlike class 1 MLCCs, it is difficult to achieve compact size for film capacitors. The table also shows how it is difficult to increase the capacitance and withstand voltage of class 1 MLCCs.

The capacitance value of class 2 MLCCs changes greatly with changes in temperature. In comparison, class 1 MLCCs exhibit a nearly linear change. The straight line slope in relation to temperature is called the "temperature coefficient." It is expressed in units of [ppm/°C].
In JIS and EIA standards, the temperature coefficient value and the related tolerance are categorized into classes. The strictest EIA standards for C0G MLCCs (class 1) require a temperature coefficient of 0 ppm/°C and a tolerance of ±30 ppm/°C at a temperature range of -55 to +125°C. Figure 2 shows temperature characteristics (changes in capacitance due to temperature change) for film capacitors and MLCCs.

As clearly shown by the graph, C0G MLCCs have extremely stable temperature characteristics when compared with X7R MLCCs (class 2), U2J MLCCs (class 1), and various film capacitors.

Reason why C0G MLCCs are used in resonance circuits

The resonance frequency (f) of LC resonance circuits with a combination of capacitors and coils (inductors) is expressed by the formula f＝1/2π√LC, where C is the capacitance of the capacitor, and L is the inductance of the coil. As shown by this formula, changes in the capacitance of the resonance capacitor (capacitor in a resonance circuit) cause changes in the resonance frequency. When the resonance frequency does not remain stable and fluctuates, warping occurs in the waveform transmitted and the energy transmission efficiency decreases.
For this reason, film capacitors which are relatively stable in relation to temperature change have normally been used in resonance circuits for automotive electronics and other devices with large currents at high voltages.
Also shown by the formula above, capacitors with even larger capacitance are required as the resonance frequency decreases. The resonance frequency for resonance circuits of automotive electronics is set to a range of several tens kHz to several hundreds kHz, and film capacitors with both a high withstand voltage and capacitance were most suitable for this usage.
However, as stated earlier, the withstand voltage and capacitance of class 1 MLCC is increasing rapidly in recent years, and more and more manufacturers are replacing film capacitors with C0G MLCCs as a result. MLCCs are smaller than film capacitors, and so have the features of increasing transmission efficiency through high-accuracy resonance and compact size.

Features:

• Higher upper limit for operating temperature range
  C0G MLCCs have an upper limit of +125°C for operating temperature range. This is optimal for automotive electronics, etc. used in the engine compartment.
• Superior moisture resistance
  C0G MLCCs possess a moisture resistance of 85°C/85%RH.
• AEC-Q200 compliance
  They comply with AEC-Q200, a global standard for reliability testing and accreditation criteria testing for automotive electronic components.
• Compact, lightweight, SMD type
  They are compact and lightweight chip components which can be mounted on the surface of boards. They save a large amount of space.
  MLCCs offer a wide range of advantages when compared to film capacitors. However, MLCCs also have the following disadvantages to be mindful of.

Cautions when replacing with MLCCs:

• Board bending and cracking
  Solder cracking is caused by stress from to board bending. In the worst-case scenario, cracking occurs in the capacitor body and possibly causing a short circuit.
• Insulation distance (creepage distance) of PCBs
  Since they are small chip components of SMD type, gaps between the land patterns mounted on the PCB are narrow, the dielectric strength voltage may be insufficient depending the usage conditions and environment.

Solutions using leaded MLCCs

The aforementioned cautions when replacing film capacitors with MLCCs can be disregarded by using leaded MLCCs (MLCCs with dipped radial leads). A leaded MLCC is a radial lead capacitor whose external electrodes have been bonded to 2 leads and coated with resin.
In addition to resolving the aforementioned problems, replacing with a lead terminal MLCC also provides the advantages of MLCCs. Replacing film capacitors with leaded MLCCs provides the advantages of MLCCs without the aforementioned problems.

Replacing film capacitors with leaded MLCCs as a solution

• Leads absorb / alleviate the stress of board deflection.
• Replacing with a leaded MLCC creates a wider gap between wire patterns and secures sufficient insulation.
  For a detailed explanation of leaded MLCCs, please refer to the following document.

Solution Guide
"Guide on Various Solutions Offered by MLCCs with Dipped Radial leads"

Automotive Grade MLCC (multilayer ceramic chip capacitor) CGA series C0G characteristics

TDK has mid voltage MLCCs (rated voltage 100 to 630V), high voltage MLCCs (rated voltage of 1000V and higher), and other MLCCs in our automotive grade CGA series. In this series, we offer the following as products with a rated voltage of 1000V, C0G temperature characteristics, and capacitances of 1nF to 33nF. In addition to resonance capacitors for magnetic resonance wireless power transfer, these MLCCs can also be used to replace film capacitors in applications which require high accuracy, such as time constraint circuits, filter circuits, oscillation circuits, etc. for downsizing and surface mount technology (SMT). Furthermore, for even greater reliability, TDK offers a MEGACAP type and a soft termination series which are highly resistant to external environmental stresses such as board bending that causes body cracks, heat shock which causes solder cracks, and vibration.
Wireless power transfer technology for efficient charging of batteries is the key to automotive evolution such as EVs and autonomous driving. In magnetic resonance wireless power transfer, resonance capacitor characteristics are closely related to power transmission efficiency. TDK's high voltage MLCCs with C0G characteristics that achieve withstand voltage of 1000V are temperature compensation (class 1) MLCCs. They possess optimal characteristics as resonance capacitors in EV wireless power transfer.
Another important element of high voltage MLCCs with C0G characteristics is extremely low ESR. TDK will continue to work at further enhancing our product lineup by improving withstand voltage, capacitance range, and other characteristics.

* C0G: From -55 to +125°C, the temperature coefficient is within 0±30ppm/°C