Accu-Guard® SMD Thin-Film Fuse ACCU-GUARD® TECHNOLOGY APPLICATIONS ® The Accu-Guard series of fuses is based on thin-film techniques. This technology provides a level of control on the component electrical and physical characteristics that is generally not possible with standard fuse technologies. This has allowed AVX to offer a series of devices which are designed for modern surface mount circuit boards which require protection. FEATURES • Accurate current rating • Fast acting • Small-standard 0402, 0603, 0805, 1206 and 0612 chip sizes • Taped and reeled • Completely compatible with all soldering systems used for SMT • Lead Free Series (F0402E, F02402G, F0603E, F0805B, F1206B) • • • • • • • • • • • Cellular Telephones Two-Way Radios Computers Battery Chargers Rechargeable Battery Packs Hard Disk Drives PDA’s LCD Screens SCSI Interface Digital Cameras Video Cameras APPROVAL FILE NUMBERS • UL, cUL: RCD#E143842 • UL (F0402G): RCD#E141069 DIMENSIONS millimeters (inches) F0603C, F0805B, F1206A and F1206B F0402E and F0603E B1 F0402G B S A B H W T T T W B2 L L L W F0402G 1.00±0.05 L (0.039±0.002) 0.58±0.04 W (0.023±0.002) 0.35±0.05 T (0.014±0.002) 0.48±0.05 B (0.019±0.002) 0.20±0.05 A (0.008±0.002) 0.05±0.05 S, H (0.002±0.002) F0402E 1.00±0.10 (0.039±0.004) 0.55±0.07 (0.022±0.003) 0.40±0.10 (0.016±0.004) 0.20±0.10 (0.008±0.004) F0603E 1.60±0.10 (0.063±0.004) 0.81±0.10 (0.032±0.004) 0.63±0.10 (0.025±0.004) 0.35±0.15 (0.014±0.006) F0603C 1.65±0.25 (0.065±0.010) 0.80±0.15 (0.031±0.006) 0.90±0.2 (0.035±0.008) 0.35±0.15 (0.014±0.006) F0805B 2.1±0.2 (0.083±0.008) 1.27±0.1 (0.050±0.004) 0.90±0.2 (0.035±0.008) 0.30±0.15 (0.012±0.006) F1206A/B 3.1±0.2 (0.122±0.008) 1.6±0.1 (0.063±0.004) 1.2±0.2 (0.047±0.008) 0.43±0.25 (0.017±0.010) F0612D 1.65±0.25 (0.065±0.010) 3.1±0.2 (0.122±0.008) 0.90±0.2 (0.036±0.008) 0.35±0.15 (0.014±0.006) HOW TO ORDER F 1206 A 0R20 F Fuse Speed Product Size Fuse Version Rated Current Fuse See table for standard sizes A=Accu-Guard® B=Accu-Guard® II C=Accu-Guard® II 0603 D=Accu-Guard® II 0612 E=Accu-Guard® II 0402, 0603 G=Accu-Guard® II 0402 Low Current Current expressed in Amps. Letter R denotes decimal point. e.g. 0.20A=0R20 1.75A=1R75 2 F=Fast W TR Termination Packaging S=Nickel/Lead-Free Solder coated (Sn 100) W=Nickel/solder coated (Sn 63, Pb 37) N=Nickel/Lead-Free Solder Coated (Sn100) TR=Tape and reel Accu-Guard® SMD Thin-Film Fuse ELECTRICAL SPECIFICATIONS Operating Temperature: -55°C to +125°C Current carrying capacity at -55°C is 107% of rating; at +25°C 100% of rating; at +85°C 93% of rating; at +125°C 90% of rating. Rated Voltage: 32V Interrupting Rating: 50A Insulation Resistance: >20MΩ guaranteed (after fusing at rated voltage) 1206 Part Number F1206A0R20FWTR F1206A0R25FWTR F1206A0R37FWTR F1206A0R50FWTR F1206A0R75FWTR F1206A1R00FWTR F1206A1R25FWTR F1206A1R50FWTR F1206A1R75FWTR F1206A2R00FWTR Current Resistance Voltage Drop Fusing Current Rating @ 10% x I rated, 25°C @ 1 x I rated, 25°C (within 5 sec.) 25°C A Ω (Max.) mV (Max.) A 0.200 0.95 350 0.40 0.250 0.75 280 0.50 0.375 0.40 220 0.75 0.500 0.35 220 1.00 0.750 0.25 220 1.50 1.000 0.18 220 2.00 1.250 0.15 220 2.50 1.500 0.11 220 3.00 1.750 0.10 210 3.50 2.000 0.065 160 4.00 Pre-Arc I2 t @ 50A A2 - sec. 0.00002* 0.00004* 0.00006 0.0002 0.003 0.005 0.009 0.02 0.035 0.04 * Current is limited to less than 50A at 32V due to internal fuse resistance. ENVIRONMENTAL CHARACTERISTICS Test Solderability Leach Resistance Storage Shear Rapid Change of Temperature Vibration Load Life 24 Conditions Components completely immersed in a solder bath at 235 ±5°C for 2 secs. Completely immersed in a solder bath at 260 ±5°C for 60 secs. 12 months minimum with components stored in “as received” packaging. Components mounted to a substrate. A force of 5N applied normal to the line joining the terminations and in a line parallel to the substrate. Components mounted to a substrate. 5 cycles -55°C to +125°C. Per Mil-Std-202F Method 201A and Method 204D Condition D. 25°C, I rated, 20,000 hrs. Requirement Terminations to be well tinned No visible damage Dissolution of termination ≤ 25% of area ΔR/R<10% Good solderability No visible damage No visible damage Δ R/R<10% No visible damage ΔR/R<10% No visible damage ΔR/R<10% Accu-Guard® SMD Thin-Film Fuse FUSE TIME - CURRENT CHARACTERISTICS FOR SIZE 1206 (TYPICAL) 10 0.20A 0.25A 0.375A 0.50A 0.75A 1.00A 1.25A 1.50A 1.75A 2.00A 1 Pre-Arc Time, Seconds 10-1 10-2 10-3 10-4 10-5 10-6 0.1 1 10 Current, Amp 100 Accu-Guard® SMD Thin-Film Fuse FUSE PRE-ARC JOULE INTEGRALS VS. CURRENT FOR SIZE 1206 (TYPICAL) 100 10 2.00A 1.75A 1.50A 1.25A 1.00A Pre-Arc I2t, A2sec 1 10-1 10-2 10-3 0.75A 0.50A � 0.375A 0.25A 0.20A 10-4 10-5 0 10 20 30 Current, Amp 26 40 50 60 Accu-Guard® SMD Thin-Film Fuse FUSE PRE-ARC JOULE INTEGRALS VS. PRE-ARC TIME FOR SIZE 1206 (TYPICAL) 100 10 Pre-Arc I2t, A2sec 1 10-1 10-2 2.00A 1.75A 1.50A 1.25A 1.00A 0.75A 0.50A 0.375A 0.25A 0.20A 10-3 10-4 10-5 10-7 10-6 10-5 10-4 10-3 10-2 Pre-Arc Time, Seconds 10-1 1 10 Accu-Guard® SMD Thin-Film Fuse QUALITY & RELIABILITY COMPONENT PAD DESIGN Accu-Guard® series of fuses is based on established thin-film technology and materials used in the semiconductor industry. • In-line Process Control: This program forms an integral part of the production cycle and acts as a feedback system to regulate and control production processes. The test procedures, which are integrated into the production process, were developed after long research and are based on the highly developed semiconductor industry test procedures and equipment. These measures help AVX/Kyocera to produce a consistent and high yield line of products. • Final Quality Inspection: Finished parts are tested for standard electrical parameters and visual/mechanical characteristics. Each production lot is 100% evaluated for electrical resistance. In addition, each production lot is evaluated on a sample basis for: • Insulation resistance (post fusing) • Blow time for 2 x rated current • Endurance test: 125°C, rated current, 4 hours Component pads must be designed to achieve good joints and minimize component movement during soldering. Pad designs are given below for both wave and reflow soldering. The basis of these designs are: a. Pad width equal to component width. It is permissible to decrease this to as low as 85% of component width but it is not advisable to go below this. b. Pad overlap 0.5mm. c. Pad extension 0.5mm for reflow. Pad extension about 1.0mm for wave soldering. HANDLING AND SOLDERING SMD chips should be handled with care to avoid damage or contamination from perspiration and skin oils. The use of plastic tipped tweezers or vacuum pick-ups is strongly recommended for individual components. Bulk handling should ensure that abrasion and mechanical shock are minimized. For automatic equipment, taped and reeled product is the ideal medium for direct presentation to the placement machine. CIRCUIT BOARD TYPE PREHEAT & SOLDERING The rate of preheat in production should not exceed 4°C/second. It is recommended not to exceed 2°C/ second. Temperature differential from preheat to soldering should not exceed 150°C. For further specific application or process advice, please consult AVX. HAND SOLDERING & REWORK Hand soldering is permissible. Preheat of the PCB to 100°C is required. The most preferable technique is to use hot air soldering tools. Where a soldering iron is used, a temperature controlled model not exceeding 30 watts should be used and set to not more than 260°C. Maximum allowed time at temperature is 1 minute. COOLING All flexible types of circuit boards may be used (e.g. FR-4, G-10). For other circuit board materials, please consult factory. After soldering, the assembly should preferably be allowed to cool naturally. In the event of assisted cooling, similar conditions to those recommended for preheating should be used. WAVE SOLDERING REFLOW SOLDERING Dimensions: millimeters (inches) 0402 0805 0603 Dimensions: millimeters (inches) 0402 0603 0805 0.8 (0.031) 1.25 (0.049) 2.1 (0.083) 0.5 (0.020) 3.1 (0.122) 0.8 (0.031) 1.7 (0.068) 0.6 (0.024) 4.0 (0.157) 1.0 (0.039) 0.59 (0.023) 0.85 (0.033) 0.6 (0.024) 1.5 (0.059) 2.3 (0.091) 0.5 (0.020) 0.6 (0.024) 1.0 (0.039) 3.0 (0.118) 1.0 (0.039) 0.85 (0.033) 0.6 (0.024) 1.25 (0.049) 1.0 (0.039) 0.8 (0.031) 0.59 (0.023) 1.5 (0.059) 1.25 (0.049) 0.8 (0.031) 1206 1206 1.25 (0.049) 0612 1.0 (0.039) 1.5 (0.059) 0612 5.0 (0.197) 1.25 (0.049) 3.1 (0.122) 2.0 (0.079) 0.6 (0.024) 3.1 (0.122) 2.0 (0.079) 3.1 (0.122) 1.0 (0.039) 1.6 (0.063) 1.6 (0.063) 28 0.6 (0.024) 0.85 (0.033) 4.0 (0.157) 1.25 (0.049) 1.5 (0.059) 0.85 (0.033) 2.3 (0.091) Accu-Guard® SMD Thin-Film Fuse RECOMMENDED SOLDERING PROFILES Care should be taken to ensure that the devices are thoroughly cleaned of flux residues, especially the space beneath the device. Such residues may otherwise become conductive and effectively offer a lousy bypass to the device. Various recommended cleaning conditions (which must be optimized for the flux system being used) are as follows: Cleaning liquids . . . . . . . .i-propanol, ethanol, acetylacetone, water, and other standard PCB cleaning liquids. Ultrasonic conditions . . . .power – 20w/liter max. frequency – 20kHz to 45kHz. Temperature . . . . . . . . . .80°C maximum (if not otherwise limited by chosen solvent system). Time . . . . . . . . . . . . . . . .5 minutes max. COMPONENT LAND TEMP (DEG C) IR REFLOW 220 210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 Assembly exits heat– no forced cooldown Additional soak time to allow uniform heating of the substrate Assembly enters the preheat zone 186°C solder melting temperature 45-60 sec. above solder melting point Soak time 1) Activates the flux 2) Allows center of board temperatures to catch up with corners 0 0.5 1 1.5 2 2.5 3 3.5 4 CLEANING RECOMMENDATIONS 4.5 Time (mins) STORAGE CONDITIONS Recommended storage prior to use are as follows: Temperature Humidity Air Pressure WAVE SOLDERING TEMPERATURE °C 3–5 seconds 260 240 220 200 180 160 140 120 100 80 60 40 20 100°C 15°C to 35°C ≤65% 860mbar to 1060mbar Natural Cooling Enter Wave Time (seconds) 0 10 20 30 40 50 60 70 VAPOR PHASE 80 90 100 110 120 Transfer from preheat with min. delay & temp. loss Preheat 215°C 200 TEMPERATURE °C conditions for Accu-Guard® 180 180 160 160 140 140 120 120 100 100 80 80 60 60 40 40 20 20 0 Reflow 215°C 200 Duration varies with thermal mass of assembly 10–60 secs typical Enter Vapor 0 Time (minutes) Natural Cooling 10 20 30 40 50 Time (seconds) 60 70 Accu-Guard® SMD Thin-Film Fuse PACKAGING Automatic Insertion Packaging Tape & Reel: All tape and reel specifications are in compliance with EIA 481-1 — 8mm carrier — Reeled quantities: Reels of 3,000 or 10,000 pieces (for F0402: 5,000 or 20,000 pieces) G MAX. B* A C E D* FULL RADIUS F *DRIVE SPOKES OPTIONAL IF USED, ASTERISKED DIMENSIONS APPLY. REEL DIMENSIONS: A(1) 180 + 1.0 (7.087 + 0.039) millimeters (inches) B* 1.5 min. (0.059 min.) C 13 ± 0.2 (0.512 ± 0.008) D* 20.2 min. (0.795 min.) E 50 min. (1.969 min.) F 9.4 ± 1.5 (0.370 ± 0.050) G 14.4 max. (0.567 max.) Metric dimensions will govern. Inch measurements rounded for reference only. (1) 330mm (13 inch) reels are available. E D F 10 PITCHES CUMULATIVE TOLERANCE ON TAPE ±0.2 C TOP TAPE W B A L P DIRECTION OF FEED CENTER LINES OF CAVITY P = 4mm except 0402 where P = 2mm CARRIER DIMENSIONS: millimeters (inches) A B C D E F 8.0 ± 0.3 3.5 ± 0.05 1.75 ± 0.1 2.0 ± 0.05 4.0 ± 0.1 1.5 +0.1 -0.0 (0.315 ± 0.012) (0.138 ± 0.002) (0.069 ± 0.004) (0.079 ± 0.002) (0.157 ± 0.004) (0.059 +0.004 -0.000 ) Note: The nominal dimensions of the component compartment (W,L) are derived from the component size. Note: AVX reserves the right to change the information published herein without notice. 30 Accu-Guard® SMD Thin-Film Fuse HOW TO CHOOSE THE CORRECT ACCU-GUARD® FUSE FOR CIRCUIT PROTECTION Correct choice of an Accu-Guard® fuse for a given application is fairly straightforward. The factor of pre-arc I2t, however, requires clarification. The proper design for pre-arc I2t is presented by way of example. DESIGN PARAMETERS 1. Operating Temperature The Accu-Guard® is specified for operation in the temperature range of -55°C to +125°C. Note, however, that fusing current is sensitive to temperature. This means that the fuse must be derated or uprated at circuit temperatures other than 25°C: Environmental Temperature Accu-Guard® Current Carrying Capacity* F0402E, F0603E F0805B, F1206A, F0805B 2.50A F1206B & 3.00A F0603C F0612D -55°C to -11°C 1.07 x IR 1.07 x IR 1.07 x IR -10°C to 60°C IR IR IR 1.07 x IR 1.07 x IR 61°C to 100°C 0.85 x IR 0.93 x IR 0.90 x IR 0.90 x IR 0.80 x IR 101°C to 125°C 0.80 x IR 0.90 x IR 0.90 x IR 0.75 x IR 0.75 x IR IR IR *As a function of nominal rated current, IR. 2. Circuit Voltage Maximum Voltage: Accu-Guard® is specified for circuits of up to rated voltage. Accu-Guard® will successfully break currents at higher voltages as well, but over voltage may crack the fuse body. Minimum Voltage: Accu-Guard® cannot be used in circuits with voltage of about 0.5V and less. The internal resistance of the fuse will limit the fault current to a value which will prevent reliable actuation of the fuse (<2 x rated current). 3. Maximum Fault Current Accu-Guard® is fully tested and specified for fault currents up to 50A. Accu-Guard® will successfully break currents above 50A, but such over current may crack the fuse body or damage the fuse terminations. 4. Steady-State Current The Accu-Guard® current rating is based on IEC Specification 127-3. In accordance with this international standard, Accu-Guard® is specified to operate at least 4 hours at rated current without fusing (25°C). Engineering tests have shown that F0805B and F1206A/B Accu-Guard® will in fact operate at least 20,000 hours at rated current without fusing (25°C). 5. Switch-on and Other Pulse Current Many circuits generate a large current pulse when initially connected to power. There are also circuits which are subject to momentary current pulses due to external sources; telephone line cards which are subject to lightning-induced pulses are one example. These current pulses must be passed by the fuse without causing actuation. These pulses may be so large that they are the determining factor for choosing the Accu-Guard® current rating; not necessarily steady state current. In order to design for current pulses, the concept of fuse pre-arc Joule integral, I2t, must be understood. Fuse current rating is defined by the requirement that 2 x IR will cause actuation in <5 seconds. This rating does not indicate how the fuse will react to very high currents of very short duration. Rather, the fusing characteristic at very high currents is specified by I2t-t curves (or I2t-I). I2t expresses the amount of energy required to actuate the fuse. Total I2t expresses the total energy which will be passed by the fuse until total cessation of current flow. Pre-arc I2t expresses that energy required to cause large irreversible damage to the fuse element (Total I2t = pre-arc I2t + arc I2t). If the Joule integral of the switch-on pulse is larger than the fuse pre-arc I2t, nuisance actuation will occur. In order to choose the proper Accu-Guard® current rating for a given application, it is necessary to calculate the I2t Joule integral of the circuit switch-on and other current pulses and compare them to the Accu-Guard® I2t-t curves. An AccuGuard® fuse must be chosen such that the pulse I2t is no more than 50% of the pre-arc I2t of the prospective fuse. Pre-arc I2t of the Accu-Guard® fuses is well characterized; I2t-t and I2t-I graphs are in this catalog. The problem is calculating the I2t of the circuit current pulses. This concept is not familiar to most engineers. Correct calculation of pulse Joule integral and subsequent choice of Accu-Guard® current rating is illustrated by way of the attached examples. Accu-Guard® SMD Thin-Film Fuse 2. Triangular current pulse The Joule integral for triangular pulse is [(Imax.)2 x t]/3, see Fig. 2a. DESIGNING FOR CURRENT PULSE SITUATIONS 1. Sine wave current pulse The Joule integral for sine wave pulse is [(Imax.)2 x t]/2, l max. see Fig. 1a. l max. t t Fig. 1a. Sine wave pulse parameters for Joule integral calculation, example #1. Thus, for the current pulse in Figure 1b, the Joule integral is [(4.8A)2 x 7.7 x 10-6 sec]/2 = 8.9 x 10-5 A2 sec. Fig. 2a. Triangular pulse parameters for Joule integral calculation, example #2. Thus, for the current pulse in Figure 2b, the Joule integral is [(1.5A)2 x 3 x 10-3 sec]/3 = 2.25 x 10-3 A2sec. 2 msec/div 10 μsec/div 0.5A/div 1A/div Fig. 1b. Sine wave pulse, example #1. Fig. 2b. Triangular pulse, example #2. The pulse duration is 7.7μsec. We must find a fuse that can absorb at least 8.9 x 10-5 X 2 = 1.8 x 10-4 A2sec Joule integral within 7.7 μsec without actuation. According to the I2t graph on page 6, pre-arcing Joule integral is 2.3x10-4 A2sec for the 0.5A fuse, which is slightly more than needed. The next lower rating (0.375A), has only 6x10-5 A2sec, which is not enough. Therefore, 0.5A fuse should be chosen for this application, see Figure 1c. The pulse duration is 3 msec. In the I2t graph on page 6, prearcing Joule integral for 3 msec pulse is 4 x 10-3A2sec for the 0.5A fuse (not enough) and 2 x 10-2 for the 0.75A fuse (more than enough). Therefore, 0.75A fuse should be chosen for this application, see Figure 2c. FUSE PRE-ARCING JOULE INTEGRALS vs. PRE-ARCING TIME 100 PRE-ARCING TIME l2t, A2 FUSE PRE-ARCING JOULE INTEGRALS vs. PRE-ARCING TIME 100 10 1 sec 10-1 10 10-2 1 10-3 10-1 10-4 10-2 10-3 PRE-ARCING TIME l2t, A2 sec 0.75A x 10-5 10-7 10-6 10-5 10-4 10-3 10-2 10-1 PRE-ARCING TIME, sec 0.5A 1 10 10-4 x 10-5 -7 -6 10 10 10-5 10-4 10-3 10-2 10-1 PRE-ARCING TIME, sec 1 10 Fig. 1c. Choice of 0.5A fuse, example #1. Pre-arcing I2t Maximum I2t design rule I2t for sample current pulse X 32 Fig. 2c. Choice of 0.75A fuse, example #2. Pre-arcing I2t Maximum I2t design rule X I2t for sample switch-on pulse Accu-Guard® SMD Thin-Film Fuse DESIGNING FOR CURRENT PULSE SITUATIONS (CONT.) 3. Trapezoidal current pulse 4. Lightning strike The Joule integral for a trapezoidal pulse is (Imin.)2 + Imin. x (Imax. - Imin.) + ( Imax-Imin)2 x t, 3 [ A lightning strike pulse is shown in Figure 4a. After an initial linear rise, the current declines exponentially. ] see Fig. 3a. l max. 0.51 max. l max. l min. t Fig. 3a. Trapezoidal pulse parameters for Joule integral calculation, example #3. Thus, for current pulse in Figure 3b, the Joule integral is: {(0.56A)2+0.56A x (1A-0.56A)+ (1A-0.56A)2 } x 3 x 10-3s = 1.9 x 10-3A2sec. 3 [ ] 0.5 msec/div t0.5 Fig. 4a. Lightning pulse parameters for Joule integral calculation, example #4. Joule integral for the linear current rise is calculated as for a triangular pulse, see example #2. The Joule integral for the exponential decline is Imax.2 x t0.5 x (-1/2In 0.5) = 0.72Imax.2 x t0.5 Thus, for the sample lightning strike pulse in Figure 4b, the total Joule integral is: (25A)2 x 2 x 10-6sec/3+0.72 x (25A)2 x 10 x 10-6sec = 4.92 x 10-3A2sec. 10 μsec/div 0.5A/div 5A/div Fig. 3b. Trapezoidal pulse, example #3. According to the I2t graph on page 6, the 0.5A fuse should be chosen for this application, see Figure 3c. FUSE PRE-ARCING JOULE INTEGRALS vs. PRE-ARCING TIME 100 PRE-ARCING TIME l2t, A2 sec Fig. 4b. Lightning strike pulse, example #4. For practical calculations, the duration of exponential decline may be assumed to be 3t0.5, because within this time 98.5% of the pulse energy is released. Thus, the total pulse duration in this example is 30 μsec, and the 1.25A fuse should be chosen for this application, see Figure 4c. 10 FUSE PRE-ARCING JOULE INTEGRALS vs. PRE-ARCING TIME 1 10-1 10-2 10-3 0.50A 100 x PRE-ARCING TIME l2t, A2 sec 10 10-4 1 10-5 10-7 10-6 10-5 10-4 10-3 10-2 10-1 PRE-ARCING TIME, sec 1 10 Fig. 3c. Choice of 0.5A fuse, example #3. Pre-arcing I2t Maximum I2t design rule X I2t for sample switch-on pulse 1.25A 10-1 10-2 x 10-3 10-4 10-5 10-7 10-6 10-5 10-4 10-3 10-2 10-1 PRE-ARCING TIME, sec 1 10 Fig. 4c. Choice of 0.5A fuse, example #4. Pre-arcing I2t Maximum I2t design rule X I2t for sample switch-on pulse Accu-Guard® SMD Thin-Film Fuse DESIGNING FOR CURRENT PULSE SITUATIONS (CONT.) 5. Complex current pulse 6. Switch-on pulse and steady-state current If the pulse consists of several waveforms, all of them should be evaluated separately, and then the total Joule integral should be calculated as well. In Figure 6a, the switch-on pulse is a triangle pulse with a 5.1 x 10-3 A2sec Joule integral of 5 msec duration; the 0.75A fuse will meet this requirement, see Figure 6b. 200 μsec/div 2 msec/div 2A/div Fig. 5a. Complex pulse, example #5. In Figure 5a, the Joule integral for the first triangle is [(4.67A)2 x 294 x 10-6sec]/3=2.14 x 10-3 A2sec and 0.75A fuse should meet this condition, see Figure 5b. FUSE PRE-ARCING JOULE INTEGRALS vs. PRE-ARCING TIME 100 Fig. 6a. Switch-on pulse and steady-state current, example #6. FUSE PRE-ARCING JOULE INTEGRALS vs. PRE-ARCING TIME 100 10 10-1 10 10-2 1 10-3 10-2 10-3 PRE-ARCING TIME l2t, A2 sec 1 PRE-ARCING TIME l2t, A2 sec 0.75A x 10-4 10-1 0.75A x x 10-5 10-7 10-6 10-5 10-4 10-3 10-2 10-1 PRE-ARCING TIME, sec 10-4 10-5 10-7 10-6 10-5 10-4 10-3 10-2 10-1 PRE-ARCING TIME, sec 1 10 Fig. 5b. Choice of fuse, example #5. Pre-arcing I2t Maximum I2t design rule X I2t for sample switch-on pulse The Joule integral for the second triangle is [(5.33A)2 x 269 x 10-6sec]/3 = 2.55 x 10-3 A2sec, and 0.75A fuse is suitable for this case also, see Figure 5b. However, for the whole pulse, the Joule integral is 4.7 x 10-3 A2sec, and the total duration is 563 μsec. For the 0.75A fuse, the Joule integral is only 8.6 x 10-3 A2sec for this pulse duration, so the 1A fuse should be chosen for this application, see Figure 5b. 34 0.5A/div 1 10 Fig. 6b. Choice of 0.75A fuse, example #6. Pre-arcing I2t Maximum I2t design rule X I2t for sample switch-on pulse The steady-state current is 0.5A, and 1A fuse is typically recommended to meet the steady-state condition. Based on steady-state current, the 1A fuse should be chosen for this application.

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