varistor products ?2010 littelfuse, inc. revision: may 11, 2010 sm20 series varistor surface mount varistors > sm20 series speci?cations are subject to change without notice. please refer to www.littelfuse.com/series/sm20.html for current information. sm20 series description the littelfuse 20mm smd series is a surface-mount metal oxide varistor device, for use in applications requiring hi-energy / transient current capability. the ac rated parts are designed to operate continuously across ac power lines. the dc rated parts are suitable for automotive applications. the series comprises a nylon molded package with folded tin plated metal leads for soldering to board. the smd series is based on radial 20mm internal varistor element with similar characteristics to the littelfuse la / za series of varistors. features ? dc voltage rating 26vdc ? ac voltage rating 175 - 320ac ? no de-rating up to 85c ambient ? lead-free, halogen- free and rohs compliant ? low voltage devices speci?ed for automotive load dump energy ? available in "waf?e" tray packaging agency approvals absolute maximum ratings ? for ratings of individual members of a series, see device ratings and speci?cations chart agency agency file number e320116 continuous sm20 series units steady state applied voltage: ac voltage range (v m(ac)rms ) 20 to 320 v dc voltage range (v m(dc) )26v transients: peak pulse current (i tm ) 8/20 s current wave, single pulse up to 6500 a single pulse energy capability (w tm ) 10/1000 s current wave 165 j load dump energy capability (td>=30ms) 160 j operating ambient temperature range (t a ) -40 to +85 o c storage temperature range (t stg ) -55 to +125 o c temperature coef?cient (a v ) of clamping voltage (v c ) at speci?ed test current <0.01 %/ o c hi-pot encapsulation (coating isolation voltage capability) (dielectric must withstand indicated dc voltage for one minute per mil-std 202, method 301) 2500 v coating insulation resistance 1000 m caution: stresses above those listed in absolute maximum ratings may cause permanent damage to the device. this is a stress o nly rating and operation of the device at these or any other conditions above those indicated in the operational sections of this s peci?cation is not implied. sm20 varistor series
varistor products ?2010 littelfuse, inc. revision: may 11, 2010 sm20 series varistor surface mount varistors > sm20 series speci?cations are subject to change without notice. please refer to www.littelfuse.com/series/sm20.html for current information. repetitive surge capability v175sm20 - V320SM20 10,000 2,000 200 100 50 20 10 5 2 500 20 100 1,000 10,000 impulse duration ( s) surge current (a) 1 2 10 4 10 5 10 6 model size 20mm v175sm20 - V320SM20 10 3 indefinite 1,000 10 2 10 5,000 1 for applications exceeding 85oc ambient temperature, the peak surge current and energy ratings must be reduced as shown below peak pulse current test waveform for clamping voltage peak current, energy and power derating curve 0 1 = virtual origin of wave t = time from 10% to 90% of peak t 1 = rise time = 1.25 x t t 2 = decay time example - for an 8/20 s current waveform: 8 s = t 1 = rise time 20 s = t 2 = decay time percent of peak value test 0 50 100 tim e t 1 t t o 1 100 90 80 70 60 50 40 30 20 10 0 -55 50 60 70 80 90 100 110 120 130 140 150 ambient temperature ( o c) percent of rated value sm20 series ratings & speci?cations maximum rating (8 5 c) speci?cations (2 5 c) continuous transient varistor voltage at 1ma dc test current maximum clamping voltage 8 x 20 s typical capacitance f = 1mhz v rms v dc energy 10 x 1000 s peak current 8 x 20 s part number branding v m(ac) v m(dc) w tm 1x pulse i tm 1x pulse v nom min v nom max v c i pk c (v) (v) (j) (a) (v) (v) (v) (a) (pf) v26sm20 26sm20 20 26 20 160 (note 1) 2000 32 (10ma) 40 (10ma) 63 20 12000 v175sm20 175sm20 175 225 90 6500 247 303 455 100 1400 v230sm20 230sm20 230 300 122 6500 324 396 595 100 1100 v250sm20 250sm20 250 330 130 6500 354 429 650 100 1000 v275sm20 275sm20 275 369 140 6500 389 473 710 100 900 v300sm20 300sm20 300 405 165 6500 420 517 775 100 800 V320SM20 320sm20 320 420 150 6500 462 540 810 100 750 1. energy rating for impulse duration of 30ms minimum to one half of peak current (automotive load dump).
varistor products ?2010 littelfuse, inc. revision: may 11, 2010 sm20 series varistor surface mount varistors > sm20 series speci?cations are subject to change without notice. please refer to www.littelfuse.com/series/sm20.html for current information. sm20 series lead (pb) soldering recommendations the principal techniques used for the soldering of components in surface mount technology are ir re-?ow and wave soldering. typical pro?les are shown on the right. the terminals of sm20 series devices are tin plated copper, and the recommended solder is 62/36/2 (sn/pb/ag), 60/40 (sn/pb) or 63/37 (sn/pb). littelfuse also recommends an rma solder ?ux. wave soldering is the most strenuous of the processes. to avoid the possibility of generating stresses due to thermal shock, a preheat stage in the soldering process is recommended, and the peak temperature of the solder process should be rigidly controlled. when using a re?ow process, care should be taken to ensure that the sm20 chip is not subjected to a thermal gradient steeper than 4 degrees per second; the ideal gradient being 2 degrees per second. during the soldering process, preheating to within 100 degrees of the solder's peak temperature is essential to minimize thermal shock. once the soldering process has been completed, it is still necessary to ensure that any further thermal shocks are avoided. one possible cause of thermal shock is hot printed circuit boards being removed from the solder process and subjected to cleaning solvents at room temperature. the boards must be allowed to cool gradually to less than 50oc before cleaning. leadCfree (pb-free) soldering recommendations the terminals of sm20 series devices are tin plated copper, and the recommended lead-free solder is 96.5/3.0/0.5 (snagcu) with an rma ?ux, though there is a wide selection of pastes and ?uxes available that should be compatible. the re?ow pro?le must be constrained by the maximums in the leadCfree re?ow pro?le. for leadCfree wave soldering, the wave solder pro?le still applies. note: the leadCfree paste, ?ux and pro?le were used for evaluation purposes by littelfuse, based upon industry standards and practices. there are multiple choices of all three available, it is advised that the customer explores the optimum combination for their process as processes vary considerably from site to site. preheat zone preheat dwell ramp rate <2c/s maximum temperature 230c temperature c time (minutes) 250 200 150 100 50 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 40-80 seconds above 183c time (minutes) 300 250 200 150 100 50 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 maximum wave 260c second preheat first preheat temperature c maximum temperature 250?c, time within 5?c of peak 20 seconds maximum preheat zone ramp rate <3?c/s 60 - 150 sec > 217?c temperature c time (minutes) 300 250 200 150 100 50 0 0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 re?ow solder pro?le wave solder pro?le leadCfree re-?ow solder pro?le
varistor products ?2010 littelfuse, inc. revision: may 11, 2010 sm20 series varistor surface mount varistors > sm20 series speci?cations are subject to change without notice. please refer to www.littelfuse.com/series/sm20.html for current information. part numbering system for varistor max voltage rating (two or three digits -- refer to ratings and speci?cations table) v 275 sm20 sm20 series
product dimensions symbol millimeters min max d (diameter) --- 26 h1 --- 10.5 h2 1. 0 - - t 0.50 0.70 s1 32.5 35 s2 3.0 4.5 w 6.2 6.6 packaging 192 mm 30 mm typical 192 mm 30 mm typical 8.4 mm typical radius 30 mm typical 11.7 mm pocket depth standard packaging is in "waf?e" trays: quantity per tray: 36 pieces quantity per box: 108 pieces
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