Multilayer Transient Voltage Surge Suppressors

ML Varistor Series

Surface Mount Varistors

146

www .littelfuse .com

Device Characteristics

At low current levels, the V-I curve of the multilayer transient voltage

suppressor approaches a linear (ohmic) relationship and shows a

temperature dependent effect (Figure 10). At or below the maximum

working voltage, the suppressor is in a high resistance mode (approach-

Ω at its maximum rated working voltage). Leakage currents at

maximum rated voltage are below 50µA, typically 25µA; for 0402 size

below 10µA, typically 5µA.

Speed of Response

The Multilayer Suppressor is a leadless device. Its response time is not

limited by the parasitic lead inductances found in other surface mount

packages. The response time of the Zinc Oxide dielectric material is less

than 1 nanosecond and the ML can clamp very fast dV/dT events such

as ESD. Additionally, in “real world” applications, the associated circuit

wiring is often the greatest factor effecting speed of response. Therefore,

transient suppressor placement within a circuit can be considered

important in certain instances.

100%

10%

25

50

75

100

FIGURE 10. TYPICAL TEMPERATURE DEPENDANCE OF THE CHARACTERISTIC

CURVE IN THE LEAKAGE REGION

o

o

o

o

GRAINS

DEPLETION

FIRED CERAMIC

DIELECTRIC

REGION

METAL

ELECTRODES

DEPLETION

REGION

METAL END

TERMINATION

FIGURE 11. MULTILAYER INTERNAL CONSTRUCTION

Energy Absorption/Peak Current Capability

Energy dissipated within the ML is calculated by multiplying the clamping

voltage, transient current and transient duration. An important advantage

of the multilayer is its interdigitated electrode construction within the mass

of dielectric material. This results in excellent current distribution and the

peak temperature per energy absorbed is very low. The matrix of semicon-

ducting grains combine to absorb and distribute transient energy (heat)

(Figure 11). This dramatically reduces peak temperature; thermal stresses

and enhances device reliability.

As a measure of the device capability in energy and peak current

handling, the V26MLA1206A part was tested with multiple pulses at its

peak current rating (150A, 8/20µs). At the end of the test, 10,000 pulses

later, the device voltage characteristics are still well within specification

(Figure 13).

100

10

20

V26MLA1206

40

60

80

100

120

140

V5.5MLA1206

0

-20

-40

-60

FIGURE 12. CLAMPING VOLTAGE OVER TEMPERATURE

100

10

0

V26MLA1206

2000

4000

6000

8000

10000

12000

NUMBER OF PULSES

FIGURE 13.

REPETITIVE PULSE CAPABILITY

PEAK CURRENT = 150A

8/20

µs DURATION, 30s BETWEEN PULSES

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