Multilayer Varistor Application Notes

Multilayer Varistor Application Notes

Multilayer Varistor Application Notes

Overview

Multilayer Varistors (MLVs) are specifically designed for suppressing electrostatic discharge (ESD).

A varistor is a voltage variable resistor that:

At low voltages has an extremely high resistance
At high voltages has a very low resistance

MLVs are made using multiple, fine grain ceramic layers of a specific formulation. To better understand the characteristics and uses of MLVs, it helps to understand the characteristics of the Metal Oxide Varistor (MOV).

Metal Oxide Varistors

MOVs are made of oxidized zinc grains and small amounts of other metal oxides between two metal electrode plates (see Figure 1). These large adjacent grains form diode junctions that allow current to flow in only one direction. These “diode junctions” arrange themselves in such a way that they perform like opposing diodes in series.

When a large voltage is applied, the grain boundaries that form the diode junctions breakdown due to electron tunneling and become conductive. This allows current and voltage through the varistor shunting the surge to ground. This action protects downstream circuits and board level components from damage. MOVs alone have generally high capacitances and lower peak current capabilities.

Multilayer Varistors

MLVs are made of fine grain ceramic layers similar to those of the MOV. These layers are stacked with alternating connections between the two electrodes. Every other layer connects to the same electrode (see Figure 2). This configuration allows for higher resistances at lower voltages with faster response times than MOVs.

eaton-multilayer-varistor-application-metal-oxide-varistor.jpg

eaton-multilayer-varistor-application-multilayer-varistor.jpg

Applications

The MLVA Family is ideal for low frequency and signal line applications.
The MLVB Family is optimal for higher frequency applications (up to 480 Mbps) or the speed commonly used in USB2.0 ports.

Both Families are also excellent for computers and peripherals, DVD players, mobile phones, digital still cameras, MP3 players, portable electronics, external storage and much more.

Features

RoHS Compliant, lead free* and halogen free constructions
IEC 61000-4-2 level 4 test for ESD protection, IEC 61000-4-4 and IEC 61000-4-5**
0201, 0402, and 0603 SMD sizes
Low and stable leakage currents to reduce power consumption
Low clamping voltages for increased circuit protection

_{* MLVA family only.}

_{** 0402 and 0603 MVLA family only}

MLVA & MLVB Specifications***

Catalog Symbols:

MLVA Family	MLVA02V--C--- (0201 size)
	MLVA04V--C--- (0402 size)
	MLVA06V--C--- (0603 size)

MLVB Family	MLVB04V--C--- (0402 size)
	MLVB06V--C--- (0603 size)

_{*** For more details, see Data Sheets 4070 (MLVA) and 4071 (MLVB) online at www.eaton.com/electronics}

Technology:

Multilayer Varistor

Electrical Characteristics:

	MLVA	MLVB
Working Voltage	5.5-26Vdc	9-18Vdc
Clamp Voltage	20-58V	35-250V
Capacitance	33-270pF	0.5-5pF

ESD Capability:

IEC61000-4-2 Direct Discharge: 8kV
IEC61000-4-2 Air Discharge: 15kV

Product Dimensions - mm:

eaton-multilayer-varistor-application-product-dimensions.png

Size	L	W	H	C
0201**	0.60±0.05	0.30±0.05	0.30±0.05	0.20±0.10
0402	1.00±0.15	0.50±0.10	0.50±0.10	0.25±0.15
0603	1.60±0.20	0.80±0.20	0.80±0.20	0.30±0.20

_{** 0402 and 0603 MVLA family only}

Design Considerations

eaton-multilayer-varistor-application-8-20-waveform.jpg

Figure 3.

8/20 μs waveform

The location in the circuit for the MLVA and MLVB families has to be carefully determined. For better performance, the device should be placed as close to the signal input as possible and ahead of any other component. Due to the high current associated with an ESD event, it is recommended to use a “0-stub” pad design (pad directly on the signal/data line and second pad directly on common ground).

In order to specify the optimum Eaton MLV Family ESD suppressor, the following need to be taken into consideration:

The clamping voltage rating on the MLV must be below the voltage the circuit can withstand without suffering damage.
The clamping voltage is the peak voltage across the MLV Family ESD suppressor at the peak current of an 8/20 μs waveform with 1 A pulse current (see Figure 3).
It is also extremely important to know the data speed of the protected circuit and/or the highest capacitance the circuit can handle without distorting the data. (The lower the capacitance rating on the MLV Family ESD suppressor, the less it will distort the data signal propagating through the circuit. Therefore the faster the data speed the lower the capacitance.)
The working voltage rating of the MLV Family ESD suppressor should be rated greater than the normal operating voltage of the circuit and not exceed 10 μA leakage current.

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