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
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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
Temperature Effect on Current Rating Temperature Effect On Current Rating
105 110
100
105
95
90
100
85
80
95
75
70 90
65
85
60
55
80
50
45
75
40
35 70
30
65
25
20
60
15
10
55
5
0 50
-55 -35 -15 5 25 45 65 85 105 125 145 -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
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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)
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% De-rating
% De-rating
2
% of Minimum I t