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V18AUMLA2220 Datasheet(PDF) 4 Page - Littelfuse |
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V18AUMLA2220 Datasheet(HTML) 4 Page - Littelfuse |
4 / 9 page 190 www .littelfuse .com Multilayer Transient Voltage Surge Suppressor AUML Varistor Series 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 recommend- ed 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 -40oC to 125oC. This capability requirement is well within the ratings of all of the AUML series (Figure 5). Further testing on the AUML series has concentrated on extending the number of load dump pulses, at rated energy, which are applied to the devices. The reliability information thus generated gives an indication of the inherent capability of these devices. As an example of device durabil- ity the 1210 size has been subjected to over 2000 pulses at its rated energy of 3 joules; the 1812 size has been pulsed over 1000 times at 6 joules and 2220 size has been pulsed at its rated energy of 25 joules over 300 times. In all cases there has been little or no change in the device characteristics (Figure 6). 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 largevolume 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 sig- nificantly lower and evenly dissipated throughout the complete device (Figure 4). This even energy dissipation ensures that there are lower peak tempera- tures 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. Experience has shown that while the effects of a load dump transient is of real concern, its frequency of occurrence is much less than those of low energy inductive spikes. Such low energy inductive spikes may be generated as a result of motors switching on and off, from ESD occur- rences, fuse blowing, etc. It is essential that the suppression technology selected also has the capability to suppress such transients. Testing on the V18AUMLA2220 has shown that after being subjected to a repetitive energy pulse of 2 joules, over 6000 times, no characteristic changes have occurred (Figure 7.) 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, zinc oxide). 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 nanosecond range, more than sufficient for the transients which are likely to be encountered in an automotive environment. RoHS 3 |
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