Reducing the number of decoupling components and conserving space with 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: use of 3-terminal feed-through filters in decoupling applications

Voltage fluctuation in the power line of an IC makes the circuit operation unstable and becomes a source of noise. To suppress this voltage fluctuation, a capacitor is inserted between the power line and ground to temporarily supply current when there is a sudden change in the load. This is called decoupling, and the capacitor used for this is called a decoupling capacitor.
The YFF-AC/AH series 3-terminal feed-through filters offer excellent performance for decoupling of the power lines of automotive electronics.

Solution: decoupling by the shunt-through method

When using a 3-terminal feed-through filter for decoupling, a special connection method called the shunt-through connection method is effective. This is a mounting method in which a 3-terminal feed-through filter is connected in parallel with the power line without cutting the wiring pattern of the power line, as illustrated in Fig. 1.
In a general feed-through connection, when current flowing in the power line increases, voltage drop also increases due to the internal resistance component (Rdc) of the 3-terminal feed-through filter. In a shunt-through connection*, a larger amount of current flows through the wiring pattern of the power line as the main flow; therefore, there is the advantage that a 3-terminal feed-through filter can be used in a circuit in which a current exists that is larger than its specified rated current.
(Shunt-through method*: In TDK, the connection method in which 3-terminal feed-through filters are connected to the power line in series is called the “feed-through” connection, and the connection method in which they are connected in parallel is called the “shunt-through” connection).

Fig. 1 : Shunt-through connection of a 3-terminal feed-through filter

Fig. 2 shows impedance-frequency characteristics when using four 0402 size MLCCs with a capacitance of 0.1μF as decoupling capacitors and when using one 0603 size automotive 3-terminal feed-through filter with a capacitance of 0.47μF (currently under development). The 3-terminal feed-through filter has low impedance even at frequencies of 20MHz or higher, achieving an excellent decoupling effect.

Fig. 2 : Comparison of the impedance-frequency characteristic of four decoupling MLCCs and one 3-terminal feed-through filter

Solution: reduced number of decoupling components and space conservation

The use of 3-terminal feed-through filter has the benefits of a reduced number of decoupling components and space conservation. As illustrated in Fig. 3, the mounting area of 2.99 mm² when using four 0402 size MLCCs is reduced to 1.28 mm² when using one 0603 size YFF-AC series 3-terminal feed-through filter, a reduction of 57.2%.

Fig. 3 : Reduced number of decoupling components and space conservation by using a 3-terminal feed-through filter

TDK's YFF-AC/AH series automotive 3-terminal feed-through filters consist 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 offer excellent performance as a countermeasure against radiation noise in power lines for automotive electronics. They are also effective as decoupling components. Since one 3-terminal feed-through filter can replace multiple decoupling MLCCs, they can achieve significant space conservation, as well as cost reduction, through the reduction of the number of necessary components.

<Major advantages, applications, and electrical characteristics of the YFF-AC/AH 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.