Ultra-small power inductors for applications using small batteries, such as wearable devices

The Metal Power Inductor PLE Series is an ultra-small power inductor with high efficiency and low leakage flux that works well when running on small batteries mounted on wearable devices.

By adopting our company's unique structural design and newly developed materials, and through thin film processing, we have achieved a high inductance of 2.2μH in a size of L:1.0×W:0.6×H:0.7mm, and a rated current of 500mA.
This report will explain its structure, features, applications and other useful information in an easy-to-understand manner.

Key technologies of PLE series

The PLE series is achieved by two key technologies.
The process technology applies the technology of thin-film HDD heads, and this time the high-precision lamination technology is improved to achieve an inductance value of more than 2.2uH on a metal power inductor with a size of 1.0 x 0.6 x 0.8mm.
In addition, as a material manufacturer, TDK develops various materials and newly develops metal magnetic materials with high magnetic permeability and low loss, realizing low-loss and high-efficiency inductors.

Figure 1: PLE key technologies

Process technology/thin film method

One of the key technologies of the PLE series is a process technology: thin film method. The thin film method has the following characteristics.

High-precision stacking is achieved, and variations can be suppressed.

Achieve more than 2 turns/layer, achieving high inductance in a small conductor dedicated area.

By ensuring the thickness of the upper and lower magnetic materials, leakage flux can be suppressed.

Figure 2 shows a comparison between the thin-film method and the coil method and the multilayer method, which are representative methods for inductors.

Figure 2: Features of thin film process

Material Technology

Another key technology of the PLE series is material technology.
This time, a newly developed high permeability/low loss metal magnetic material was used, and after optimization, high Q was achieved in the 1~2.5MHz frequency band. The higher the Q, the lower the ACR, which can achieve higher power efficiency.

Figure 3: Characteristics of new magnetic materials

Effect of PFM's Hi-Q characteristics

Small battery-driven wearable devices require low power, so the power drive method uses PFM (Pulse Frequency Modulation).
Compared with PWM (Pulse Width Modulation), PFM has the advantage of reducing power because the DC bias current is small, but the AC bias current becomes larger. (Figure 4)
Therefore, the ACR characteristic becomes very important, and using a Hi-Q, low ACR inductor can achieve higher power efficiency. (Figure 5)

Figure 4: Comparison of PFM and PWM

Figure 5: PFM power efficiency differences

Leakage flux and its effect on noise

The PLE series makes it easy to ensure the thickness of the magnetic material, which can suppress leakage flux.
Furthermore, by making the direction of the magnetic flux generated by the coil horizontal relative to the substrate, it is possible to suppress the influence of the magnetic flux on the GND plane, which is the cause of noise, and suppress noise.
The measurement results of the influence of the magnetic flux on the GND plane of the horizontal coil and the vertical coil are shown in Figure 6.

Figure 6: Effect of magnetic flux on ground

	PLEA67BBA2R2 Horizontal	PLEA67BBA2R2 Vertical

Main Application

The above requires lightweight equipment

Small devices that use small batteries to realize circuits with higher efficiency than DC-DC converters

The above wearable devices

The above requires lightweight equipment

Key Features and Benefits

High magnetic permeability, low loss metal material

High-precision laminated thin-film inductors

Ultra-small size, high inductance

Magnetic flux flows parallel to the GND plane, so noise is low

Main Specifications