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.