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Multi-layer Slow Blow Fuses Help Protect Automotive Infotainment Systems Multi-layer Slow Blow Fuses
Help Protect Automotive Infotainment
Automotive infotainment designs must provide adequate power protection over an increasingly
broad range of voltages, currents and temperatures. While the manufacturers primary design goal
may be to improve and expand product functionality, a good design will also focus on product
survivability across all definable environments. Many automotive-centric devices, such as navigation
systems, DVD players and Bluetooth® enabled devices, must be able to function in a harsh
environment where voltage transients and temperature extremes are common, yet unpredictable.
Infotainment devices may control multiple functions with integrated modules controlling audio, video,
communications and power distribution. These modular designs are usually predicated on form
constraints as well as cost-to-repair concerns. An intelligent power distribution design that protects each
module with a current limiting device can help improve customer satisfaction and reduce warranty costs.
High inrush currents and elevated temperatures are two of the major threats to equipment powered
by the automotive bus. When selecting a fuse for vehicle infotainment systems, the designer must
make derating considerations for operating current, pulse withstand, and application temperature.
Power-on and other system operations, such as processor speed changes, or motor start-up, may cause voltage or current spikes, resulting
in nuisance blows. Over time, repeated surges may result in fuse fatigue. Extreme temperatures can cause degradation of the circuit
protection devices performance.
Many devices, once exposed to repeated overtemperature conditions, may no longer perform to specification and may begin to draw
higher and higher currents in order to maintain functionality. With enough of these degraded components incorporated into a system
design, the inrush currents may begin to exceed even the most conservative design criteria.
Selecting a fuse with slow blow characteristics, high current carrying capability, and high pulse withstand is critical in such designs.
APPLICATION NOTE
www.circuitprotection.com
Multi-layer Fuse Design
Tyco Electronics Slow Blow surface-mount fuses are designed to
help
protect
electronic
systems
with
very
dynamic
current
requirements. We offer a fuse line with small size, high reliability,
strong arc suppression characteristics, and some of the highest
current ratings available in the 1206 and 0603 form factors.
Slow Blow Fuses help provide overcurrent protection on systems
that experience large and frequent current surges as part of their
normal operation, and feature clear time characteristics of:
4 hours minimum at 100% of rated current;
120 seconds maximum and 1 second minimum at 200% of
rated current;
3 seconds maximum and 0.1 second minimum at 300% rated
current; and
ranges from 0.0005 seconds minimum to 0.05 second
maximum at 800% of rated current.
The multi-layer design of these devices allows fuse elements to
be stacked in parallel within a single device. The elements are
embedded within the fuse body and surrounded on all sides by
arc
suppression
material.
Figure
1
compares
the
multi-layer
design of Tyco Electronics Slow Blow Fuses with a typical single
layer, glass coated design.
The ability to stack fuse elements in parallel allows greater
current handling capacity within a given package size. The multi-
layer design also has the benefit of exposing more fuse element
surface area to the glass-ceramic arc suppression material. When
the fuse elements open, there is more material to absorb the
vaporized fuse element, resulting in a very efficient and effective
quenching of the fuse arc.
Figure 1. Multi-layer fuse vs. single-layer, glass coated fuse design
Glass/Ceramic
Substrate
Multiple Fuse
Elements
Substrate
Material
Single Fuse
Element
Single-layer Glass Coated Design
Multi-layer Design
Glass
Coating Temperature 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.
Transient State or Pulse Derating
The term pulse is used to describe any type of transient current
that may be applied to the fuse. Common examples of pulses are
inrush currents observed at system power-on, motor start-up
currents and more extended duration peak currents observed
during high-speed processing activity in computing systems.
These pulses have an effect on the fuse element because the
transient heating they induce causes thermal cycling within the
device. Pulses can affect the life of the fuse. Therefore, the pulse
energy and the number of times the fuse may be subjected to the
pulses must be considered.
The I
2
t parameter provides a measure of the fuses ability to
withstand the energy of a pulse. By determining the I
2
t energy of
the pulse, it can be compared to the fuses I
2
t curve to determine
what the rated current of the fuse must be to help ensure reliable
fuse performance.
Once
the
I
2
t
value
for
the
application
waveform
has
been
determined, the device must be derated based on the thermal
environment and the number of cycles expected over the system
lifetime.
Since
the
stress
induced
by
the
current
pulse
is
cumulative 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 3 presents the current pulse-derating
curve for Tyco Electronics surface mount chip fuses up to
100,000 cycles.
Raychem, TE Logo and Tyco Electronics are trademarks. All information, including illustrations, is believed
to be reliable. Users, however, should independently evaluate the suitability of each product for their
application. Tyco Electronics makes no warranties as to the accuracy or completeness of the information,
and disclaims any liability regarding its use. Tyco Electronics only obligations are those in the Companys
Standard Terms and Conditions of Sale for this product, and in no case will Tyco Electronics be liable for any
incidental, indirect, or consequential damages arising from the sale, resale, use or misuse of the product.
Specifications are subject to change without notice. In addition, Tyco Electronics reserves the right to make
changeswithout notification to Buyerto materials or processing that do not affect compliance with any
applicable specification.
© 2008 Tyco Electronics Corporation. All rights reserved. RCP0025E.0408
Raychem Circuit Protection Products
308 Constitution Drive, Building H
Menlo Park, CA USA 94025-1164
Tel
: (800) 227-7040, (650) 361-6900
Fax : (650) 361-4600
www.circuitprotection.com
www.circuitprotection.com.hk (Chinese)
www.tycoelectronics.com/japan/raychem (Japanese)
Themal Derating Curve
-55 -45 -35 -25 -15
-5
5
15
25
35
45
55
65 70
85
95 105
115
125
110
100
90
80
70
60
50
40
30
20
10
0
Maximum Operating Temperature (C)
%
o
f
C
a
r
r
y
i
n
g
C
u
r
r
e
n
t
C
a
p
a
c
i
t
y
88%
Figure 2. Tyco Electronics Slow Blow Fuse Thermal Derating Curve
Pulse Derating Curve
100
1000
10,000
100,000
100%
10%
Number of Pulses
%
o
f
M
i
n
i
m
u
m
I
2
t
Figure 3. Tyco Electronics Slow Blow Fuse Pulse Derating Curve
Thermal derating curves can be used to determine the derating
percentage based on operating temperature. Figure 2 shows the
thermal derating curve for Tyco Electronics Slow Blow Fuses.
The minimum fuse current rating selection is determined by the
following formula:
I
fuse
(I
sys
/0.75)/K
temp
Where:
K
temp
is the temperature derating factor
Tyco Electronics Slow Blow Fuse provides some of the highest
current ratings available in the 1206 and 0603 footprints and
enhances high-temperature performance in a wide range of
circuit protection designs. Each power circuit within a modular
automotive infotainment system can be individually protected
with a single device. The RoHS-compliant device is designed for
operating
temperatures
between
55°C
and
+125°C,
and
withstands
soldering
temperatures
of
up
to
260°C
for
60
seconds maximum.
To determine the specific Tyco Electronics 1206SFS or 0603SFS
Slow
Blow
Fuse
for
your
application,
please
refer
to
http://circuitprotection.com/slowblow.asp for the latest product
information and Fuse Selection Guide.
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