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Application Note
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Application Note
While smartphones, TWS, and other mobile devices are becoming smaller and more sophisticated, devices and ICs are becoming more vulnerable to electrostatic discharge (ESD), surges, and other types of immunity. These mobile devices are increasingly being hand-held, operated, and worn. Therefore, ESD countermeasures are needed more than ever, while ESD protection components are also increasingly being used to prevent ESD. TDK offers a lineup of chip varistors as components that can protect circuits from ESD. Lastly, using actual devices, this article presents examples of ESD countermeasures using chip varistors for actual failures that occur when ESD enters a device.

What is a Varistor?

Chip varistors are ceramic semiconductor products based mainly on zinc oxide. As the figure below shows, chip varistors have a laminated structure, with breakdown voltage and capacitance being controlled by the number of layers and the interlayer design. It is a voltage-dependent nonlinear resistive element whose resistance decreases rapidly when a voltage above a certain value is applied. A varistor is equivalent to two series-connected Zener diodes and has no polarity.

Figure 1 What is a Varistor?

●Internal structure of chip varistor

●Equivalent circuit of chip varistor

●Comparison of voltage-current characteristics between chip varistor and Zener diode

Measuring ESD on an Actual Equipment

We conducted experiments by mounting an LED on an actual device and checked how the LED light changes as the ESD enters, depending on whether the LED has an ESD protection component (with or without a chip varistor). The application of ESD to the device with mounted LED was performed through electrostatic immunity testing using the human body model (HBM) of IEC61000-4-2, which specifically assumes that charged electrical charges are discharged into electronic devices (see Figures 2 and 3).

Figure 2: Evaluation Conditions

ESD Test Conditions

 ● IEC61000-4-2 (150pF, 330Ω)
 ● Contact Discharge:1 kV to 8 kV
 ● ESD Strike Count: 10 at 1 second intervals

Figure 3 Measurement Settings

Evaluation Results

The table and video show the ESD test results with and without a chip varistor on a device with LED (see Figure 4).
In the presence of a chip varistor, the LED lit up to up to 8 kV ESD discharge.
On the other hand, when an ESD protection element is not used, the LED momentarily turned off at 4 kV to 6 kV ESD discharge. Furthermore, the LED completely turned off at 7 kV ESD discharge.
This result confirms that the LED is affected by ESD. Furthermore, it demonstrated that the chip varistor was capable of protecting the LED from ESD.

Figure 4 Evaluation Results
Test Condition 1kV 2kV 3kV 4kV 5kV 6kV 7kV 8kV
1)With Varistor (a) (a) (a) (a) (a) (a) (a) (a)
2)Without Varistor (a) (a) (a) (b) (b) (b) (c) -

The LED kept good condition
up to 8kV using varistor

(a)The LED kept lighting
(Not broken)

(b)The LED went out just for a moment
(about to be broken)

(c)The LED went out
(completely broken)

*The “tik tak” sound indicated the time of applied ESD.
*This particular product has a blinking LED for normal operation and is not due to the application of ESD.

Product Introduction

TDK’s lineup of multilayer chip varistors is mainly for consumer electronics and automotive applications.
For consumer applications, varistors are available in sizes as small as EIA01005 (0.4 x 0.2 mm).
For automotive applications, varistors for mass production come in sizes as small as EIA0402 (1.0 x 0.5 mm).
To summarize, the use of TDK's multilayer chip varistors saves space and allows a high degree of freedom in the mounting layout.
In addition, multilayer chip varistors for automotive applications are available in AEC-Q200, 125°C, and 150°C versions, allowing customers to select a highly reliable and optimal product to suit their applications.

Product Lineup for LED
Item Break Down Voltage
V1mA [V]
Maximum Continuous Voltage
Vdc [V]
Operating Temperature
range [℃]
AVRM0402C120MT330N 12 5.5 8kV(Level4) -40 to +85
AVRM0603C080MT101N 8 5.5 8kV(Level4) -40 to +85
AVRM0603C120MT101N 12 5.5 8kV(Level4) -40 to +85
AVR-M1005C080MTAAB 8 5.5 8kV(Level4) -40 to +85
AVR-M1005C120MTACC 12 7.5 8kV(Level4) -40 to +85
B72590D0150H060 (LED) 23 15 8kV(Level4) -40 to +85
AVRH10C270KT350NA8 27 19 25kV -55 to +150
AVRH10C390KT500NA8 39 28 25kV -55 to +150
B72590D0360B060 45 36 8kV(Level4) -40 to +85
B72590D0201B060 600 200 8kV(Level4) -40 to +85
AVR-M1608C220KT2AB 22 16 25kV -40 to +125
AVRM1608C720KT750M 72 53 25kV -55 to +150
AVR-M2012C220KT6AB 22 16 25kV -40 to +125
AVRM2012C720KT201M 72 53 25kV -55 to +150