Surface-mount Fuses Fundamentals Surface-mount Fuses Fundamentals Overview TE Circuit Protection offers the widest selection of surface-mount fuses available for addressing a broad range of overcurrent protection applications. Helping to prevent costly damage and promote a safe environment for electronic and electrical equipment, our single-use chip fuses provide performance stability to support applications with current ratings from .5A up to 20A. TE Circuit Protection also offers the telecom FT600 fuse for telecommunications applications. This telecom fuse helps comply with North American overcurrent protection requirements, including Telcordia, GR-1089, TIA-968-A (formerly FCC Part 68), and UL60950 3rd edition. Multi-layer Design for Chip Fuses The multi-layer design has the benefit of exposing more fuse Figure 1 element surface area to the glass-ceramic absorption material. Glass/Ceramic Multiple Fuse Substrate Single Fuse Glass When the fuse elements open, there is more material for the Substrate Elements Material Element Coating vaporizing fuse metals to absorb into, resulting in a very efficient and effective quenching of the fuse arc. Figure 1 compared the multi-layer design of our SFF fuses with standard glass coated designs. The glass coated designs rely on Multi-layer Design Single-layer Glass Coated Design the coating on only one side of the fuse element to absorb the vaporizing fuse material when it opens. Therefore, there is much less absorption material available to absorb the fuse metals. The Figure 2 Fault Zones result can be prolonged arcing and possible coating breach. Figure 2 shows how the absorption characteristics of the two 11 designs differ. The multi-layer design indicates a clean separation with the fuse element evenly diffusing into the surrounding ceramic substrate. In the glass coated design, the element diffusion takes place in a small portion of the device and is only Multi-layer Design Single-layer Glass Coated Design absorbed by the glass material directly above the area of failure. Wire-In-Air Design for 2410SFV Fuses The 2410(6125) is a Wire-In-Air SMD Fuse which is very suitable Figure 3 for secondary level over current protection applications. Glass fiber enforced epoxy body Figure 3 compared our straight wire element design 2410SFV fuses with normal corrugating wire design fuse. The straight wire Straight wire element element in air performs consistent fusing and cutting characteristics together with excellent inrush current withstanding capability. Copper terminal plated with Ni and Tin Introduced PCB assembly technology into 2410SFV fuses design and manufacture, we achieved on lead free completely and no end cap falling off risk comparing with traditional ceramic body Ceramic body with end cap fuse. Corrugate wire element End cap plated with Tin 75Temperature Derating A fuse is a temperature sensitive device. Therefore, operating temperature will have an effect on fuse performance and lifetime. Operating temperature should be taken into consideration when selecting the fuse current rating. The Thermal Derating Curve for surface mount fuses is presented in Figure 4. Use it to determine the derating percentage based on operating temperature and apply it to the derated system current. Figure 4 1206/0603/0402 Series 2410 Series Themal Derating Curve Temperature Effect On Current Rating 110 110 100 105 100 90 95 80 88% 90 70 85 60 80 50 75 40 70 30 65 20 60 10 55 0 50 -55 -45 -35 -25 -15 -5 5 15 25 35 45 55 65 70 85 95 105 115 125 -55 -35 -15 5 25 45 65 85 105 125 Maximum Operating Temperature (C) Maximum Operating Temperature (C) Pulse Cycle Derating 2 Once the I t value for the application waveform has been Figure 5 determined, it must be derated based on the number of cycles Surface-mount Fuse Pulse Derating Curve 100% expected over the system lifetime. Since the stress induced by the current pulse is mechanical in nature, the number of times the stress is applied has significant bearing on how much derating must be applied to the fuse rating. Figure 5 presents the current pulse derating curve for our surface-mount chip fuses up to 100,000 cycles. 10% 100 1000 10000 100000 Number of Pulses Selecting Surface-mount Fuses 11 Fuse selection seems straightforward, in that, you pick one which has a current rating just a bit higher than your worstcase system operating current. Unfortunately, its not that simple. There are derating considerations for operating current and application temperature. Turn-on and other system operations (like processor speed changes or motor start up) cause current surges or spikes that also require consideration when selecting a fuse. So selecting the right fuse for your application is not as simple as knowing the nominal current drawn by the system. Fuse Selection Flowchart However, the basic considerations for fuse selection are shown in the flowchart presented in Figure 6. Following this flow chart will help you select a fuse best suited for your application conditions. Figure 6 Step 1 Apply Standard Steady Apply Steady State Determine Steady State State Derating (75%) Temperature Derating Fuse Current Fuse Current Rating I I /0.75 I I /0.75/K Rating fuse sys fuse sys temp Step 2 Step 3 Step 4 Step 5 Step 6 Determine Pulse Apply Pulse Apply Pulse Apply Derating Select Fuse Current Waveform by Cycle Derating Temperature for Variance in Rating for Pulse 2 Calculating I t Derating the Circuit Environment Step 7 Select Fuse Current Rating Step 8 Check Voltage Rating (use higher value between Step 1 and Step 6) 76 % of Carrying Current Capacity % De-rating 2 % of Minimum I t