Application of ferrite beads in small portable devices

Foreword

With the popularity of mobile phones, portable music players, and portable game consoles, the design of these electronic devices has been demanded to be more compact, high-performance, low-energy, and low-noise. Therefore, a large number of ultra-small-sized capacitors, resistors, and EMI suppression filters are widely used in these small portable devices.

The chip ferrite bead has a simple structure and is widely used for EMI squelch because of its small size and convenient use. Murata has been able to mass produce 0402 size (1.0 & TImes; 0.5mm) sheet ferrite beads BLM15 series, 0201 size (0.6 & TImes; 0.3mm) BLM03 series. However, in order to achieve the same squelch effect as a large-sized product, it is necessary to increase the number of coils inside the magnetic beads and increase the impedance value thereof. As a result, the DC resistance increases and the power consumption of the circuit increases. This has become a problem that must be solved.

By developing new materials and improving the processing technology, Murata successfully developed a small low-DC resistance product, and the 0402-size chip ferrite bead BLM15AX series was reduced by 60% compared with the previous products. As a result, this series of products saves power consumption in small portable device circuits and extends battery life.

Introduced here is the new sheet-like ferrite bead BLM15AX series.

1 characteristic needs

In small portable devices, in order to suppress noise, the ferrite bead needs to have both a small size of a patch type and a large impedance value, thereby achieving efficient squelch characteristics and low power consumption. From the above points, the characteristics of the characteristics of the ferrite bead can be summarized as follows, as shown in Figure 1.

Figure 1: Characteristics of ferrite beads

Figure 2 shows the DC resistance and resistance distribution (catalog specification) of ferrite beads on the market. The thick arrows in the figure indicate that the ferrite bead will pursue low DC resistance and high impedance values ​​in the future.

The specifications of the previous 0402 sheet-like ferrite bead BLM15AG series (shown by ● in the figure) are distributed below the table compared with the sheet-like ferrite beads (shown in ◆ in the figure). This time, the BLM15AX series achieves the industry's lowest resistance specification (see ○ in the figure).

Figure 2: Specification distribution of flaky ferrite beads


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