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 benet of exposing more fuse
Figure SF1
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 efcient
and effective quenching of the fuse arc.
Figure SF1 compares 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 SF2
Fault Zones
result can be prolonged arcing and possible coating breach.
Figure SF2 shows how the absorption characteristics of the two
designs differ. The multi-layer design indicates a clean separation
with the fuse element evenly diffusing into the surrounding
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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 that is suitable for
Figure SF3
secondary level overcurrent protection applications. Glass Fiber Enforced
Epoxy Body
Figure SF3 compares our straight wire element design
2410SFV fuses with normal corrugated wire design fuse.
Straight Wire Element
The straight wire element in air provides consistent fusing
and cutting characteristics together with inrush current
Copper Terminal
withstanding capability.
Plated with Ni and Tin
By introducing PCB assembly technology into the 2410SFV fuse
design and manufacturing process, lead-free compliance has
Ceramic Body
been achieved without the problems associated with end caps
on traditional ceramic devices.
Corrugated Wire Element
End Cap Plated with Tin
RoHS Compliant, ELV Compliant HF Halogen Free
107
2013_CP_S10-Fuses-1-Fundamentals.indd 107 8/3/13 10:58 AMTemperature Derating
A fuse is a temperature sensitive device. Therefore, operating temperature will have an efect 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 SF4. Use it to determine the derating percentage based on
operating temperature and apply it to the derated system current.
Figure SF4
1206/0603/0402 Series 2410 Series
Temperature Effect on Current Rating Temperature Effect on Current Rating
110
110
105
100
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 determined,
Figure SF5
it must be derated based on the number of cycles expected over
Surface-mount Fuse Pulse Derating Curve
100%
the system lifetime. Since the stress induced by the current pulse is
mechanical in nature, the number of times the stress is applied has
signicant bearing on how much derating must be applied to the fuse
rating. Figure SF5 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
Fuse selection seems straightforward, in that you pick one which has a current rating just a bit higher than your worst case
system operating current. Unfortunately, it is 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
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simple as knowing the nominal current drawn by the system.
Fuse Selection Flowchart
However, the basic considerations for fuse selection are shown in the ow chart presented in Figure SF6. Following this ow
chart will help you select a fuse best suited for your application conditions. For a detailed example of this process you can
download our Fuse Selection Guide available on our website.
Figure SF6
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)
RoHS Compliant, ELV Compliant HF Halogen Free
108
2013_CP_S10-Fuses-1-Fundamentals.indd 108 8/14/13 9:21 AM
% Derating
% Derating
2
% of Minimum I t