Chip Varistors Applications for ESD Countermeasures

By Tomáš Zedníček
10 months Ago

This technical article written by TDK discusses the optimal chip varistor applications for ESD countermeasures.

Characteristics of Chip Varistors

Chip varistors have both surge absorption capabilities and noise suppressing effects.

The following figure shows the equivalent circuit of a chip varistor.

The chip varistor is equal to the one where the capacitor is connected parallelly to the two Zener diode elements that are connected opposite to each other.

*Figure 1　The equivalent circuit of a chip varistor*

Equivalent to the circuit where the two Zener diode elements are connected opposite to each other and the capacitor is connected parallelly. The current-voltage characteristics are symmetric and have no polarity.

*Figure 2　A comparison between the noise level and frequency characteristic example*

Chip varistors achieve both noise suppression and ESD suppression.

Optimal Applications for Chip Varistors

The following figure shows the application field of the various components for ESD countermeasures. This article introduces excellent applications especially for chip varistors.

The optimal applications for chip varistors are in the blue region.

*Figure 3　The optimal applications for components for ESD countermeasures*

Optimal Applications for Multilayer Chip Varistors

Audio circuits (Headphone, Mic, Speaker)

TVS diodes are sources of noise in audio lines, and increasing output to raise volume degrades sound quality. Chip varistors are the optimal solution in audio lines.

*Figure 4　Result of THD+N measurement for each ESD protection component*

*Figure 5　Range of multilayer chip varistors suitable for audio circuits (headphones, mics, speakers)*

Countermeasures against counter electromotive force (Solenoid valve, Motor, etc.)

TDK’s chip varistors feature excellent resistance to repeated surges, and products with characteristics that compare well with zener diodes are also available as automotive grade AVR series.

*Figure 6　Effects on varistor voltage due to repeated applications of surges*

*Figure 7　Range of multilayer chip varistors suitable for countermeasures against counter electromotive force (solenoid valves, motors, etc.)*

Comparison between chip varistors and MLCCs as ESD protection

When the capacitance of the protection components is in the 100pF range, the ESD protection capacity of chip varistors becomes extremely high compared to multilayer chip capacitors.