Solution Guide (1/4)

MLCC(Multilayer Ceramic Capacitors)・C0G Guide for Resonance Circuits Vol.1 Features of High voltage MLCCs with C0G Characteristics and Replacement Solutions

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 (type 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.

Characteristics of main capacitors

MLCCs are divided into two major categories according to the type of ceramic materials used for their dielectric, namely type 1 (temperature compensating) and type 2 (high dielectric constant). Type 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 type 1 MLCCs do not offer as high a capacitance as type 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 (type 1 and type 2).

Figure 1: Corresponding regions of rated voltage-capacitance for different capacitors

Overlapping regions of Regions with further increases MLCC and film capacitors in withstand voltage and capacitance

100k

10k

Film capacitor

1k MLCC (type 1)

100

R a ted volt ge (V) Aluminum MLCC (type 2) electrolytic 10 capacitor

1 1pF 1nF 1µF 1mF Capacitance

In terms of capacitance, type 2 MLCCs achieve a capacitance of more than 100µF, as offered by aluminum electrolytic capacitors. Furthermore, even in the past, type 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 film capacitors, and MLCCs.

Table 1: Comparison of characteristics in main capacitors Film MLCC MLCC capacitor (type 1) (type 2) Large capacitance ◎ △ ○ Withstand voltage ◎○○ Temperature characteristics ◎ ◎ △ Frequency characteristics ○◎◎ ESL characteristics ○ ◎ △ DC bias characteristics ◎◎◎ Moisture resistance ○ ◎ ◎ Lifespan/reliability ◎◎◎ Compact size △ ◎ ◎ ◎: Outstanding ○: Good △: Fair

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MLCC(Multilayer Ceramic Capacitors)・C0G Guide for Resonance Circuits Vol.1 Features of High voltage MLCCs with C0G Characteristics and Replacement Solutions

The advantage of aluminum electrolytic capacitors is their large capacitance. In terms of other characteristics, film capacitors and MLCCs are superior. Unlike type 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 type 1 MLCCs.

The capacitance value of type 2 MLCCs changes greatly with changes in temperature. In comparison, type 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 (type 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.

Figure 2: Comparison of temperature characteristics (changes in capacitance due to temperature change) in C0G MLCCs and various capacitors

10

5

0 C0G MLCCs have stable temperature characteristics with a capacitance change rate of nearly 0% between –55°C and +125°C.

C0G MLCC (type 1) U2J MLCC (type 1) –5 X7R MLCC (type 2) C a p cit nce ch nge r te (%) Film capacitor (PPS: Polyphenylene Sulfide) Film capacitor (PEN: Polyethylene Naphthalate) Film capacitor (PET: Polyethylene Terephthalate) Film capacitor (PP: Polypropylene) –10 –60 –30 030 60 90 120 Temperature (℃)

As clearly shown by the graph, C0G MLCCs have extremely stable temperature characteristics when compared with X7R MLCCs (type 2), U2J MLCCs (type 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＝1/2√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 type 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. There are also NP0 MLCCs with an upper limit of +150°C. These can be used in ECU (electronic control units), etc. directly mounted on the engine. ●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.

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MLCC(Multilayer Ceramic Capacitors)・C0G Guide for Resonance Circuits Vol.1 Features of High voltage MLCCs with C0G Characteristics and Replacement Solutions

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"

Figure 3: Replacing SMD MLCCs with leaded MLCCs (MLCCs with dipped radial leads) as a solution

Lead terminal type

MLCC Insulating resin

SMD type Solder joint

MLCC Solder joint Leads absorb the stress of board bending Lead wire

Land Board Lead wire gap

《Problems with surface mounting》 《Replacing with a leaded MLCC as a solution》 ▲Solder cracks occur from board bending, cracks occur in the capacitor ●Leads absorb the stress of board deflection body ●Replacing with a leaded MLCC creates a wider gap between wire patterns and secures ▲Insufficient insulation between the land patterns when high voltage is sufficient insulation applied

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MLCC(Multilayer Ceramic Capacitors)・C0G Guide for Resonance Circuits Vol.1 Features of High voltage MLCCs with C0G Characteristics and Replacement Solutions

Automotive Grade MLCC (multilayer ceramic chip capacitor) CGA series C0G characteristics / NP0 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 / NP0 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 (type 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.

External dimensions Temperature Series Rated voltage Capacitance (L×W) characteristics

3.2×2.5mm C0G 1000V 1nF to 22nF CGA6 (EIA 1210)

5.7×5.0mm C0G、 1000V 10nF to 33nF CGA9 (EIA 2220) NP0

 C0G：From –55 to +125°C, the temperature coefficient is within 0±30 ppm/°C NP0：From –55 to +150°C, the temperature coefficient is within 0±30 ppm/°C

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MLCC(Multilayer Ceramic Capacitors)・C0G Guide for Resonance Circuits Vol.2 Application to EV wireless power transfer systems

Through advancements in materials technology, multilayer technology, etc., MLCCs (multilayer ceramic chip capacitors) are becoming smaller and achieving higher capacitance. Amidst these circumstances, in recent years, there have also been significant increases in withstand voltage and capacitance of MLCCs used in temperature compensation (type 1). TDK has developed high voltage MLCCs with C0G characteristics. Through C0G characteristics, these MLCCs achieve a withstand voltage of 1000V at the broadest capacitance range (1nF to 33nF) in the industry. Even in fields where film capacitors have traditionally been used, replacement with MLCCs is now possible for use in resonance circuits, etc. In addition to explaining the characteristics of C0G MLCCs with high withstand voltage, this section focuses on the advantages of replacing the film capacitors used in EV wireless power transfer systems.

Example of replacing film capacitors with MLCCs: EV wireless power transfer systems

The use of wireless power transfer stated on a large scale with smartphones and is spreading to other devices. The C0G MLCCs produced by TDK feature compact size and superior temperature characteristics. Therefore, they are widely used as resonance capacitors in wireless power transfer for mobile devices. TDK is engaged in technological development for wireless power transfer in EVs (electric vehicles). From the perspective of environmental issues and fuel economy, major automotive manufacturers throughout the world are focusing on EVs as the most prevalent eco cars, and a variety of EV models are being developed. An essential aspect of popularizing EVs is improving infrastructure, such as charging facilities, and increasing driving distance. In terms of charging infrastructure, an increasing number of charging stands are being installed in parking lots at highway service areas/parking areas, airports, and shopping malls. An especially promising type of charging infrastructure is wireless power transfer systems which enable non-contact charging. Furthermore, wireless power transfer is also an essential technology for practical implementation of autonomous driving. In addition to electromagnetic induction wireless power transfer for charging built-in batteries in mobile devices, in recent years, TDK has been one of the first companies to start developing magnetic resonance wireless power transfer technology. Until now, we have supported needs in industrial equipment such as automated guided vehicles (AGV), elevators, etc. The EV wireless power transfer introduced in this section is an advanced magnetic resonance system that utilizes TDK's magnetic material technology and dielectric technology.

Principles and features of magnetic resonance wireless power transfer

The system of the widely used electromagnetic induction wireless power transfer is equivalent to structures in which transformer cores are divided and gaps are opened. The advantage of this method is that it can be achieved at a low cost. However, the transmitting efficiency decreases drastically when the gap between the transmission coil and receiving coil becomes large. As the distance between the coils increases, a portion of the magnetic flux becomes leakage flux, which weakens magnetic coupling between coils. Magnetic coupling is expressed as the coupling coefficient (k). The coupling coefficient is in the range of 0≦k≦1. The ideal value, without leakage flux, is 1. It decreases as leakage flux increases from an increase in the gap between coils or a shift of the coil center, and it ultimately declines to 0. Magnetic resonance wireless power transfer was developed as a method for overcoming these disadvantages. In the magnetic resonance method, an LC resonance circuit is formed by inserting capacitors in both the transmission side and receiving side, thus achieving power transmission which matches the resonance frequency of the transmission side and receiving side. This method maintains a high transmitting efficiency even in conditions with a low coupling coefficient due to slight widening of the distance between coils or a shift of center position, etc. The basic principles of this method are shown in Figure 1.

Figure 1: Basic principles of magnetic resonance wireless power transfer

Resonance capacitor Resonance capacitor

Magnetic coupling via LC resonance

Load / battery Transmission Receiving coil coil High-frequency power s upply

Transmission Receiving side side

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MLCC(Multilayer Ceramic Capacitors)・C0G Guide for Resonance Circuits Vol.2 Application to EV wireless power transfer systems

High-power resonance capacitors are an important component in magnetic resonance using wireless power transfer EV charging systems. This is because a high-accuracy resonance circuit with high withstand voltage is required for efficient wireless transfer of a large amount of power in a short time. Film capacitors are one valid option as capacitors that satisfy these requirements. However, for EVs that require further downsizing and weight reduction in order to increase cruising distance and achieve a more spacious vehicle cabin, a significant advantage is achieved through replacement with C0G MLCCs that save space. Previously, there were no products which achieved withstand voltage of 1000V with C0G characteristics. However, the high voltage MLCCs with C0G characteristics developed by TDK can now be used as effective replacements.

Achieved even greater reductions in size and weight by replacing with 1000V C0G MLCC

Figure 2 shows an image of EV battery charging using magnetic resonance wireless power transfer, and a size comparison of resonance capacitors on the receiving side.

Figure 2: EV battery charging using magnetic resonance wireless power transfer & size comparison of resonance capacitors for the receiving side (image)

By using magnetic resonance, power is transmitted 1000V C0G MLCCs achieve even greater savings in space by requiring a smaller quantity. from the transmission coil to the receiving coil and the battery is charged.

Film capacitor (Capacitance=20nF, AC2kVrms)

Charging Controller

630V C0G MLCC Receiver (15×12=180 pcs.)

wiring Transmitter 1000V C0G MLCC (10×8=80 pcs.)

If using multiple TDK C0G MLCCs connected in serial and parallel arrays to replace film capacitors which satisfy the specifications of capacitance 20nF and AC 2kVrms, you would need 180 of the conventional 630V C0G MLCCs. This equates to a significant savings in space. However, when replacing with the newly-developed 1000V C0G MLCCs, simple calculations indicate that only 80 MLCCs would be required, saving even more space.

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MLCC(Multilayer Ceramic Capacitors)・C0G Guide for Resonance Circuits Vol.2 Application to EV wireless power transfer systems

Enables significant reduction in the number of MLCCs used through extremely low ESR

Figure 3 shows a comparison of impedance-frequency characteristics and ESR-frequency characteristics for the conventional 630V C0G MLCC and the newly-developed 1000V C0G MLCC.

Figure 3: Comparison of impedance-frequency characteristics and ESR-frequency characteristics for 630V MLCC and 1000V MLCC

100 The 1000V MLCC has a 50% lower ESR than the 630V MLCC. This enables a significant reduction in the number of resonance 10 capacitors necessary.

1 Impedance

0.1 ESR

0.01

ESR( Ω ) / imped a nce ( 3225/C0G/630V/22nF ESR:2mΩ(100k to 1MHz) 0.001 3225/C0G/1000V/22nF ESR:1mΩ(100k to 1MHz) 0.0001 100k 1M 10M 100M Frequency (Hz)

Compared to the 630V MLCC, the ESR for the 1000V MLCC is 50% less. When the rated voltage is increased from 630V to 1000V, the current flowing through a single MLCC increases by approximately 1.5 times. If the ESR value is equivalent to conventional MLCCs, there is an increased risk of lifespan degradation from heat generation. Since the newly-developed 1000V C0G MLCC has a 50% lower ESR, as shown by the replacement example in Figure 2, it is possible to achieve the significant reduction of 180 MLCCs to 80. This clearly shows the importance of the ESR value when using MLCCs to replace other capacitors.

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MLCC(Multilayer Ceramic Capacitors)・C0G Guide for Resonance Circuits Vol.2 Application to EV wireless power transfer systems

Automotive Grade MLCC (multilayer ceramic chip capacitor) CGA series C0G characteristics / NP0 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 / NP0 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 (type 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.

External dimensions Temperature Series Rated voltage Capacitance (L×W) characteristics

3.2×2.5mm C0G 1000V 1nF to 22nF CGA6 (EIA 1210)

5.7×5.0mm C0G、 1000V 10nF to 33nF CGA9 (EIA 2220) NP0

 C0G：From –55 to +125°C, the temperature coefficient is within 0±30 ppm/°C NP0：From –55 to +150°C, the temperature coefficient is within 0±30 ppm/°C

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MLCC(Multilayer Ceramic Capacitors)・C0G Guide for Resonance Circuits Vol.3 Application to EV plug-in power charging systems

Thanks to increased capacitance, increased high withstand voltage, and other advancements in MLCCs (multilayer ceramic chip capacitors), replacement with MLCCs is now possible even in fields where film capacitors are used. For usage which requires a high level of precision and reliability, C0G MLCCs used in temperature compensation (type 1) with particularly outstanding temperature characteristics offer a variety of replacement merits including significant space savings. In a temperature range of -55 to +125°C, C0G characteristics meet the very strict standards of a temperature coefficient of 0 ppm/°C and a tolerance of ±30 ppm/°C. Through C0G characteristics, TDK's high voltage MLCCs with C0G characteristics achieve withstand voltage of 1000V at the broadest capacitance range (1nF to 33nF) in the industry. The solution guide "Guide for Replacing Film Capacitors with MLCCs (Vol. 2)" explained EV wireless power transfer systems. However, for the time being, it is certain that the plug-in method will play a leading role in the popularization of EVs. This method charges the battery of EVs (BEVs/PHVs) from household AC power supplies. Therefore, this section mainly explains the advantages of using MLCCs to replace film capacitors in the onboard chargers (OBC) of plug-in charging systems.

Onboard chargers are required for plug-in charging

The differences between HEVs and EVs (BEVs) are summarized in Figure 1.

Figure 1: Comparison of HEVs and EVs (BEVs)

HEV EV(BEV),PHV Normal charging Commercial AC current On Board Charger Outlet Engine

Motor Inverter Motor Inverter Battery Battery Transmission Transmission BMS

Rapid charging inlet

Drive system: fuel engine + electric motor Drive system: electric motor Battery voltage: 150 to 300 V Battery voltage: about 400 V to 600 V or higher

The biggest difference is that while HEVs run using the combination of a fuel engine and an electric motor, EVs use only an electric motor. Consequently, a system for charging the vehicle battery from an external power supply is essential for EVs. Cruising distance increases concurrently with increases in battery capacity. For that reason, the trend is for EV battery size to increase. Furthermore, as a result of desire for a shorter charging time, there is a trend of increasing battery voltage.

《Characteristics of EVs (BEVs》 ●Battery size is larger than in HEVs. To increase cruising distance, battery size tends to increase. ●EV batteries have a voltage of about 400V to 600V or higher, compared to a voltage of about 150V to 300V in HEVs. ●Onboard chargers are required for charging from commercial AC current. ●A BMS (battery management system) for processing several kW of power is required.

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MLCC(Multilayer Ceramic Capacitors)・C0G Guide for Resonance Circuits Vol.3 Application to EV plug-in power charging systems

Basic structure and function of onboard chargers

There are two types of EV plug-in power charging systems: rapid charging and normal charging. Rapid charging systems are installed as charging stands at highway service areas / parking areas, large commercial facilities, etc. Rapid charge systems use three-phase AC current sent from high-voltage charging facilities. These systems have the advantage of a short charging time. However, the systems require a dedicated infrastructure and are expensive. Normal charging systems use commercial AC current. Charging is performed via a cable connecting the EV to external outlets of homes, etc. Although this method takes longer than rapid charging, it eliminates the inconvenience of going to a charging stand and has the advantage of enabling inexpensive charging at home at any time. However, when using plug-in charging, since it is not possible to charge the battery using AC current, it is necessary to use the onboard charger to convert to DC current. The basic principles of onboard chargers are shown in Figure 2.

Figure 2: Basic structure of onboard charger (OBC)

《Onboard charger (OBC)》

《AC block》《PFC block》《DC/DC block》

EMC Power DC-DC Motor filter factor Battery converter inverter rectification correction Commercial AC current

First, commercial AC current is rectified and smoothed in the AC block of the onboard device. Next, the power is sent to the DC-DC converter via the PFC (Power Factor Correction / harmonic current suppression circuit) block. The DC-DC converter changes the input voltage to an appropriate output voltage and then charges the battery. Onboard charger DC-DC converters are used at a higher voltage than DC-DC converters installed in general electronic devices, and they also require a high conversion rate in order to increase cruising distance. Consequently, more and more manufacturers are using LLC resonance DC-DC converters (hereinafter referred to as "LLC converters").

Example of replacing with MLCC: resonance capacitor of LLC converter

Figure 3 shows an example circuit (full bridge type) for a current resonance LLC converter used in an onboard charger.

Figure 3: Example circuit (full bridge type) for current resonance LLC converter

DC input Transformer for LLC resonance power supply Resonance capacitor DC output

Cr Lr

Lm

Cr: Resonance capacitor LLC resonance circuit Lr: Leakage inductance Control circuit Lm: Excitation inductance

Lr and Lm are the leakage inductance and excitation inductance of the transformer respectively, and compose the resonance circuit along with the capacitor Cr. The name "LLC converter" is used because the converter is composed of two inductances (L, L) and a capacitor (C). Since a resonance capacitor is connected in series to the transformer in this circuit, this type is known as a serial resonance converter or a current resonance converter. Normal DC-DC converters employ the PWM (pulse width modulation) method, in which they obtain the required output voltage by controlling the width of pulse current sent to the transformer at a certain switching frequency. On the other hand, the LLC converter uses the PFM (pulse frequency modulation) method, which controls the switching frequency while maintaining a fixed pulse width. Therefore, the resonance capacitor requires superior characteristics.

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MLCC(Multilayer Ceramic Capacitors)・C0G Guide for Resonance Circuits Vol.3 Application to EV plug-in power charging systems

Little variation in capacitance and tanδ ; optimal as a resonance capacitor

Since LLC converters have a PFM power supply which uses LC resonance, transformers and resonance capacitors are both extremely important components. The following types of characteristics are required in resonance capacitors which are used in the LLC capacitors of onboard chargers.

《Characteristics required in resonance capacitors of LLC converters》 ●Superior temperature characteristics Since the resonance capacitors are used in resonance circuits, it is extremely important that the capacitance change caused by temperature fluctuations is small. ●Superior withstand voltage characteristics LLC converters are power supplies appropriate for use with relatively high power. However, since larger voltage rectangular waves than those in general electronic devices are applied, high withstand voltage (rated voltage) is required. ●Superior ESR characteristics Since a large current flows in resonance circuits, superior ESR is required.

In the past, film capacitors were normally used as resonance capacitors in the LLC converters of onboard chargers. This was because film capacitors have a good balance of withstand voltage and relatively high capacitance. However, in recent years, MLCCs have been developed with characteristics that approach the region of film capacitors, and there is an increasing need for a replacement for film capacitors in automotive electronics. MLCCs are divided into two major categories according to their type of dielectric, namely type 1 (temperature compensating) and type 2 (high dielectric constant). Since type 1 MLCCs have a small capacitance change caused by temperature, and possess outstanding frequency characteristics, they are used in circuits, etc. which require high precision. Among type 1 MLCCs, C0G MLCCs have extremely superior temperature characteristics, making them optimal as resonance capacitors. Another advantage of C0G MLCCs is that they are smaller than film capacitors.

Automotive Grade MLCC (multilayer ceramic chip capacitor) CGA series C0G characteristics / NP0 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 / NP0 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 (type 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.

External dimensions Temperature Series Rated voltage Capacitance (L×W) characteristics

3.2×2.5mm C0G 1000V 1nF to 22nF CGA6 (EIA 1210)

5.7×5.0mm C0G、 1000V 10nF to 33nF CGA9 (EIA 2220) NP0

 C0G：From –55 to +125°C, the temperature coefficient is within 0±30 ppm/°C NP0：From –55 to +150°C, the temperature coefficient is within 0±30 ppm/°C

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