How to use the "YFF Series" 3-Terminal Feed-through filter for noise suppression and reducing the number of MLCCs

The appearance and internal structure of the 3-terminal feed-through filter are illustrated in the conceptual diagram.
Although it is generally called ""3-terminal"", it is actually composed of two terminal electrodes and two ground electrodes. It has an internal structure in which internal electrodes for conduction and internal electrodes for grounding are alternately layered.

Capacitors for reducing high-frequency noise must have a low ESR (Equivalent Series Resistance) and ESL, as well as a higher SRF (Self Resonant Frequency).
ESR and ESL are influenced by the resistance and inductance of terminal electrodes and internal electrodes.
Therefore, a reverse geometry capacitor, in which a low ESL is achieved by reversing the longitudinal direction and width direction of the terminal electrodes of a normal 2-terminal multilayer ceramic chip capacitor (MLCC) to make the current route wider and shorter, is also effective as a noise countermeasure.
TDK's YFF series 3-terminal feed-through filter achieves even lower ESR and ESL compared to these reverse geometry capacitors.
Figure 2 shows a comparison of the impedance-frequency characteristics and ESL values of TDK's 2-terminal MLCC, reverse geometry capacitor, and the 3-terminal feed-through filter.

We will introduce solution examples for decoupling, filter, and DC/DC converter applications.

Voltage fluctuations in the power supply line can destabilize circuit operation and cause noise. To address this, a capacitor is inserted between the power supply line and ground, providing a temporary supply of current to suppress voltage fluctuations when the load changes suddenly.
This is known as decoupling, and the capacitors used for this purpose are called decoupling capacitors.
In recent years, the number of decoupling capacitors required to clear the target impedance has been increasing due to the higher power consumption, higher frequencies, and lower voltages associated with the miniaturization of SoCs. The YFF series 3-terminal feed-through filter, characterized by low ESL, is effective in reducing the number of capacitors needed when replacing conventional 2-terminal capacitors.

We will demonstrate a reduction in the number of components using a 3-terminal feedthrough filter for decoupling applications using a PI simulation.
Here, we compare impedance data as seen from the SoC side.
A common feature between the configurations before and after the proposal is that three 22uF MLCCs are connected to the DC/DC converter for smoothing.

With the recent increase in the operating frequency of power ICs, high-frequency noise has become a problem, causing abnormal operation of the set.
As a common countermeasure, a C-L-C π-type filter is configured on the power line.
However, incorporating a 3-terminal feed-through filter into the filter's capacitor can achieve a higher attenuation effect.
Figure 8 shows the results of transfer characteristics obtained through simulation, while Figure 9 presents the conducted noise (voltage method) measured in different noise modes using the actual DC/DC converter.
Please note that for the conducted noise voltage method in Figure 9, measurements were taken in all three configurations with our common mode filters installed as a common mode countermeasure.

The switching frequency of the DC/DC converter has been increased from the conventional several hundred kHz to over 2 MHz,
as shown below, in order to reduce component size, obtain faster response, and avoid interference with the AM radio frequency band.
As a result, the frequencies of ripple noise and ringing noise are also increasing, creating a demand for broadband noise suppression measures up to the high frequency range of several hundred MHz.
In this case study, we introduce the effects of using 3-terminal feedthrough filters on both the input and output sides of the DC/DC converter to suppress power fluctuations and reduce the number of components.

The input terminal of the DC/DC converter can generate significant high-frequency noise due to switching noise from wiring and IC parasitic components, leading to Nth-order harmonics from the fundamental frequency. This noise may radiate into external circuits. To address this, it is usually necessary to suppress the noise at its source, often by placing a small ceramic capacitor near the IC. Here, we present an example of a DC/DC converter using a 3-terminal feed-through filter. In this design, the 3-terminal feed-through filter is used as a noise countermeasure close to the IC. Both configurations include a 2-terminal MLCC 10uF capacitor placed on both sides of the input terminal.

On the output side of a DC/DC converter, significant high-frequency noise can also be generated due to Nth harmonics from the fundamental frequency and parasitic components of wiring and ICs, which can radiate to external circuits.
With the reduction in SoC voltage, the margin between maximum and minimum voltage has decreased. Additionally, as devices become more functional, more systems are becoming sensitive to high-frequency noise. In addition to addressing the issue on the SoC side, it is considered desirable to implement countermeasures on the power supply IC side, which is the source of the noise. Conventionally, an effective method for noise suppression was to arrange multiple 2-terminal MLCCs in stages. However, here we introduce an example where power supply fluctuations can be suppressed by using TDK's large-capacity 3-terminal feed-through filter. Both configurations include a 2-terminal MLCC 47uF capacitor as the output capacitor.