Varistor Metal Oxide Varistor Products Page 56 Varistor Metal-Oxide Varistor Products

2017 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 09/14/17 Metal-Oxide Varistors (MOVs) Surface Mount Multilayer Varistors (MLVs) > AUML Series AUML Load Dump Pulsing over a Temperature Range of -55C to +125C V(10mA) 35 30 25 20 15 10 5 0 0 1 2 3 4 5 6 7 8 9 10 1 12 VOLTAGE # OF LOAD DUMPS 2220 = 25J 1812 = 6J 1210 = 3J Figure 6 Speed of Response The clamping action of the AUML suppressor depends on a conduction mechanism similar to that of other semiconductor devices (i.e. P-N Junctions). The apparent slow response time often associated with transient voltage suppressors (Zeners, MOVs) is often due to parasitic inductance in the package and leads of the device and less dependent of the basic material (Silicon, Z N O). Thus, the single most critical element affecting the response time of any suppressor is its lead induc-tance. The AUML suppressor is a surface mount device, with no leads or external packaging, and thus, it has virtually zero inductance. The actual response time of a AUML surge suppressor is in the 1 to 5 ns range, more than sufficient for the transients which are likely to be encountered in an automotive environment. Multilayer Internal Construction Temperature Effects In the leakage region of the AUML suppressor, the device characteristics approaches a linear (ohmic) relationship and shows a temperature dependent affect. In this region the suppressor is in a high resistance mode (approaching 10 6 ) and appears as a near open-circuit. Leakage currents at maximum rated voltage are in the microamp range. When clamping transients at higher currents (at and above the 10mA range), the AUML suppressor approaches a 1-10 characteristic. In this region the characteristics of the AUML are virtually temperature independent. Figure 3 shows the typical effect of temperature on the V-I characteristics of the AUML suppressor. Load Dump Energy Capability A Load Dump transient occurs when the alternator load in the automobile is abruptly reduced. The worst case scenario of this transient occurs when the battery is disconnected while operating at full rated load. There are a number of different Load Dump specifications in existence in the automotive industry, with the most common one being that recommended by the Society of Automotive Engineers, specification #SAE J1113. Because of the diversity of these Load Dump specifications Littelfuse defines the Load Dump energy capability of the AUML suppressor range as that energy dissipated by the device itself, independent of the test circuit setup. The resultant Load Dump energy handling capability serves as an excellent figure of merit for the AUML suppressor. Standard Load Dump specifications require a device capability of 10 pulses at rated energy, across a temperature range of -40C to +125C. This capability requirement is well within the ratings of all of the AUML Series (Figure 6 on next page). The very high energy absorption capability of the AUML suppressor is achieved by means of a highly controlled manufacturing process. This technology ensures that a large volume of suppressor material, with an interdigitated layer construction, is available for energy absorption in an extremely small package. Unlike equivalent rated Silicon TVS diodes, the entire AUML device volume is available to dissipate the Load Dump energy. Hence, the peak temperatures generated by the Load Dump transient are significantly lower and evenly dissipated throughout the complete device (Figure 5 below). This even energy dissipation ensures that there are lower peak temperatures generated at the P-N grain boundaries of the AUML suppressor. There are a number of different size devices available in the AUML Series, each one with a load dump energy rating, which is size dependent. Figure 5

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