source: TDK TechNote
TDK has released today a technical article on The Optimal Applications for Chip Varistors 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.
Figure 8 The ESD absorption waveforms of a multilayer ceramic chip capacitor and a multilayer chip varistor with the same capacitance
Figure 9 Applications where the capacitance of components for ESD countermeasures is about 100pF
Recommended chip varistors by application
The chip varistors in the table below for the applications other than those shown above are recommended products. The optimal products for applications according to size and circuit voltage can be selected from the table below. All products have shown good performance with each application.
- ESD Protection Devices Selection Guide (Commercial Grade)
- ESD Protection Devices Selection Guide (Automotive Grade)