PRODUCT | HIGHLIGHT
Novel Chip Varistor Combines ESD, EMI Protection
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n innovative chip varistor that provides both electrostatic discharge (ESD) and electromagnetic interference (EMI) protection has been developed by TDK Corporation. By optimizing its internal structure, the AVRF101U6R8KT242 chip varistor enables both ESD and EMI protection. This product is intended for audio equipment that uses wireless communications in the 2.4GHz band, such as Wi-Fi and Bluetooth, and supports high sound quality. The company has started mass production of the chip varistor.

AVRF101U6R8KT242 chip varistors for audio equipment
Photo 1: AVRF101U6R8KT242 chip varistors for audio equipment
Demonstration of sound quality evaluation of the chip varistor for audio equipment
Photo 2: Demonstration of sound quality evaluation of the chip varistor for audio equipment
In general, the abnormal voltage of ESD or lightning surge applied to devices, such as ICs or electronic equipment induces malfunction or breaks devices and equipment. Chip varistors, the resistance value of which changes in accordance with the applied voltage, are used to protect devices and equipment against abnormal voltage. The varistors’ role is protection against ESD. Digital circuits of today have reduced withstand voltage due to finer fabrication, and they are vulnerable to breakage due to ESD. In particular, it is difficult to implement shielding against ESD using a chassis in small equipment and devices with external interface terminal, such as Universal Serial Bus (USB) sticks, and therefore, protection components are generally used.

Conventionally, for this application, Zener diodes have been widely used. However, as small and low-priced multilayer chip varistors have been developed, varistors have emerged as an ESD protection component.

Specific Features
The chip varistor for audio equipment has a capacitance of 6.8pF±10 percent, ESD protection capability equivalent to IEC61000-4-2 Level 4, and allowable circuit voltage of DC 28V, enabling use in high-power Class-D amplifiers.

The chip varistor provides EMI protection in addition to ESD protection through the optimization of its internal structure, such as elements and internal electrodes, to secure attenuation characteristics in the 2.4GHz band. Insertion loss of -20dB has been secured in the 2.4GHz band, enabling Time Division Multiple Access (TDMA) noise countermeasure. The varistor also contributes to the improvement of reception sensitivity of wireless communications.

Applications of the chip varistor for audio equipment
Fig. 1: Applications of the chip varistor for audio equipment
Internal structure of multilayer chip varistors
Fig. 2: Internal structure of multilayer chip varistors
TDMA noise refers to unpleasant audible noise called buzz generated in part by high-frequency communication signals from an antenna intruding into a microphone line through an earphone microphone cord. It is called TDMA noise because it has been a problem in the communication of the TDMA system.

The chip varistor is of the 1005 size, which is a full-fledged general-purpose size in high-density packaging. It can be easily mounted on small equipment.

Therefore, the adoption of the chip varistor is expected in areas, in which high sound quality is pursued, such as microphones, speakers and receiver circuits that use the 2.4GHz band, such as Wi-Fi and Bluetooth.

In the future, TDK intends to expand its product lineup, while pressing forward with the expansion of the chip size and the applicable frequency range.