Countermeasure Against Radiation Noise in Power Line Using 3-Terminal Feed-Through Filters

Solution Guides

With the increasing speed and wave frequency in electronics, further reduction of ESL (equivalent series inductance) is required for capacitors, or 3-terminal feed-through filters must be used for noise filtering or decoupling. Furthermore, the need for low-ESL type products is increasing in electrical systems of automobiles in order to improve safety and comfort, and to support infotainment systems. Through a series of articles, we will introduce various solutions for automobile electronics using TDK's advanced low-ESL components.

Outline: using 3-terminal feed-through filters as a countermeasure against radiation noise in power lines of automotive electronics

DC-DC converters are frequently used as power supplies for automotive electronics, such as electronic control units (ECUs).
A feature of DC-DC converters is their high-efficiency. However, they are switching power supplies, and radiation noise is generated in them by the switching of semiconductors. This radiation noise has an adverse effect on other electrical systems and causes reception interference in AM/FM radios and digital terrestrial television broadcasting (DTB). In addition, ECUs have increasingly become concentrated in engine compartments and dashboards, and they are easily affected by each other’s radiation noise.
The basic concept of EMC countermeasures is to cut off noise from its source. In order to realize comfortable car connectivity and self-driving systems, power lines of automotive electronics need thorough countermeasures against radiation noise.
TDK's YFF-A series automotive 3-terminal feed-through filters consists of EMC countermeasure components featuring high reliability and support for high current, developed specially for automotive electronics through optimization of material and design. Since they exhibit a good attenuation characteristic over a broad frequency range while being compact, they are extremely effective as a countermeasure against radiation noise in power lines for automotive electronics.

DC-DC converters in ECUs are the major source of radiation noise

There are over 100ECUs incorporated in high class cars. These ECUs are connected by wire harnesses that bundle the power line from the battery and signal lines for exchanging information among the ECUs.
Fig.1 shows the main sources of noise and noise propagation paths in an in-vehicle network.

Fig. 1 : Main noise sources in the power line of an in-vehicle network

Solution: Countermeasures against radiation noise in power lines of automotive electronics

The radiation noise countermeasure provided by TDK's YFF-A series 3-terminal filters in power lines of automotive electronics is evaluated below.
Fig. 2 illustrates an evaluation circuit for examining radiation noise from the power line of a piece of automotive electronic equipment and a schematic of the measurement system using a 3 m anechoic chamber. A DC power supply (12 V) representing an automotive battery and an evaluation circuit (DUT: device under test) are connected by a cable, and the radiation noise level (electric field intensity) is measured by an antenna located 3 meters away.

Fig. 2 : Evaluation circuit and measurement system using 3 m anechoic chamber for radiation noise in a power line

The requirements for electromagnetic interference (EMI) testing for protecting in-vehicle receivers such as radios or TVs are prescribed by the international electromagnetic compatibility (EMC) standard CISPR 25. These requirements are much stricter than those for consumer equipment.
In the above evaluation circuit, the frequency-electric field intensity (radiation noise level) characteristics were compared where no filter was inserted, where a 4-terminal low-pass filter (LPF) was inserted, and where a 3-terminal feed-through filter was inserted (Fig. 3). The red frames indicate the limits of the radiation noise level in the FM band and DTB band, prescribed by the extremely strict CISPR 25 Class 5.

Fig. 3: Radiation noise suppression effect of a 3-terminal feed-through filter

When no filter was used, noise greatly exceeded the limits in the DTB band. However, when an LPF or 3-terminal feed-through filter was inserted, the noise level was suppressed below the limits. The LPF is a 4-element filter consisting of two MLCCs, a chip bead, and a metal coil. On the other hand, the 3-terminal feed-through filter can satisfy the requirements of CISPR25 Class 5 as just one element. 3-terminal feed-through filters offer an extremely advantageous solution in terms of component cost, mounting cost, and reduced mounting space.

<Major advantages, applications, and electrical characteristics of the YFF-A series automotive 3-terminal feed-through filters>

[Major advantages]

Compact and high-performance EMC countermeasure components specialized for automotive applications. Also demonstrate an excellent effect for decoupling use.
Compliant with AEC-Q200
Realize a good noise attenuation characteristic over a broad frequency range
Support large current (6 to 10 A)
Reduce the number of components, mounting cost, and mounting space, and simplify the PCB layout.

[Major uses]

EMC countermeasure and decoupling in power lines for various automotive electronics such as ECUs, car navigation systems, in-vehicle camera systems, millimeter wave radar systems, etc.