2
Accu-Guard®
SMD Thin-Film Fuse
ACCU-GUARD®TECHNOLOGY
The Accu-Guard®series of fuses is based on thin-film tech -
niques. This technology provides a level of control on the com -
po nent electrical and physical characteristics that is generally
not pos si ble with standard fuse technologies. This has allowed
AVX to offer a series of devices which are designed for mod-
ern 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)
APPLICATIONS
• 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
HOW TO ORDER
DIMENSIONS millimeters (inches)
L
T
B
1
W
B2
F0402G F0402E F0603E F0603C F0805B F1206A/B F0612D
L 1.00±0.05 1.00±0.10 1.60±0.10 1.65±0.25 2.1±0.2 3.1±0.2 1.65±0.25
(0.039±0.002) (0.039±0.004) (0.063±0.004) (0.065±0.010) (0.083±0.008) (0.122±0.008) (0.065±0.010)
W 0.58±0.04 0.55±0.07 0.81±0.10 0.80±0.15 1.27±0.1 1.6±0.1 3.1±0.2
(0.023±0.002) (0.022±0.003) (0.032±0.004) (0.031±0.006) (0.050±0.004) (0.063±0.004) (0.122±0.008)
T 0.35±0.05 0.40±0.10 0.63±0.10 0.90±0.2 0.90±0.2 1.2±0.2 0.90±0.2
(0.014±0.002) (0.016±0.004) (0.025±0.004) (0.035±0.008) (0.035±0.008) (0.047±0.008) (0.036±0.008)
B 0.48±0.05 0.20±0.10 0.35±0.15 0.35±0.15 0.30±0.15 0.43±0.25 0.35±0.15
(0.019±0.002) (0.008±0.004) (0.014±0.006) (0.014±0.006) (0.012±0.006) (0.017±0.010) (0.014±0.006)
A 0.20±0.05
(0.008±0.002)
S, H 0.05±0.05
(0.002±0.002)
F0603C, F0805B, F1206A and F1206B
B
T
L
W
F0402G
L
T
S
W
AB
H
F0402E and F0603E
F
Product
Fuse
1206
Size
See table for
standard sizes
A
Fuse Version
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
0R20
Rated Current
Current expressed in
Amps. Letter R denotes
decimal point. e.g.
0.20A=0R20
1.75A=1R75
F
Fuse
Speed
F=Fast
W
Termination
S=Nickel/Lead-Free
Solder coated
(Sn 100)
W=Nickel/solder coated
(Sn 63, Pb 37)
N=Nickel/Lead-Free
Solder Coated (Sn100)
TR
Packaging
TR=Tape and reel
24
Accu-Guard®
SMD Thin-Film Fuse
ELECTRICAL SPECIFICATIONS
Operating Tem per a ture: -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)
Test Conditions Requirement
Solderability Components completely immersed in a Terminations to be well tinned
solder bath at 235 ±5°C for 2 secs. No visible damage
Leach Resistance Completely immersed in a solder bath Dissolution of termination
at 260 ±5°C for 60 secs. ≤ 25% of area
ΔR/R<10%
Storage 12 months minimum with components Good solderability
stored in “as received” packaging.
Shear Components mounted to a substrate. No visible damage
A force of 5N applied normal to the
line joining the terminations and in
a line parallel to the substrate.
Rapid Change of Components mounted to a substrate. No visible damage
Temperature 5 cycles -55°C to +125°C. Δ R/R<10%
Vibration Per Mil-Std-202F No visible damage
Method 201A and ΔR/R<10%
Method 204D Condition D.
Load Life 25°C, I rated, 20,000 hrs. No visible damage
ΔR/R<10%
1206
Current Resistance Voltage Drop Fusing Current Pre-Arc
Part Number Rating @ 10% x I rated, 25°C @ 1 x I rated, 25°C (within 5 sec.) 25°C I2t @ 50A
A Ω (Max.) mV (Max.) A A2- sec.
F1206A0R20FWTR 0.200 0.95 350 0.40 0.00002*
F1206A0R25FWTR 0.250 0.75 280 0.50 0.00004*
F1206A0R37FWTR 0.375 0.40 220 0.75 0.00006
F1206A0R50FWTR 0.500 0.35 220 1.00 0.0002
F1206A0R75FWTR 0.750 0.25 220 1.50 0.003
F1206A1R00FWTR 1.000 0.18 220 2.00 0.005
F1206A1R25FWTR 1.250 0.15 220 2.50 0.009
F1206A1R50FWTR 1.500 0.11 220 3.00 0.02
F1206A1R75FWTR 1.750 0.10 210 3.50 0.035
F1206A2R00FWTR 2.000 0.065 160 4.00 0.04
* Current is limited to less than 50A at 32V due to internal fuse resistance.
ENVIRONMENTAL CHARACTERISTICS
Accu-Guard®
SMD Thin-Film Fuse
0.20A
0.25A
0.375A
0.50A
0.75A
1.00A
1.25A
1.50A
1.75A
2.00A
10-1
1
10
0.1 1 10
Current, Amp
Pre-Arc Time, Seconds
100
10-2
10-3
10-4
10-5
10-6
FUSE TIME - CURRENT CHARACTERISTICS
FOR SIZE 1206 (TYPICAL)
26
Accu-Guard®
SMD Thin-Film Fuse
10-1
1
10
100
Pre-Arc I2t, A2sec
Current, Amp
10-2
10-3
10-4
10-5
5040
3020100 60
2.00A
1.75A
1.50A
1.25A
1.00A
0.75A
0.50A
�
0.25A
0.375A
0.20A
FUSE PRE-ARC JOULE INTEGRALS VS. CURRENT
FOR SIZE 1206 (TYPICAL)
Accu-Guard®
SMD Thin-Film Fuse
10-1
1
10
100
Pre-Arc I2t, A2sec
Pre-Arc Time, Seconds
10-2
10-3
10-4
10-5
10-7 10-6 10-5 10-4 10-3 10-2 10-1 110
2.00A
1.75A
1.50A
1.25A
1.00A
0.75A
0.50A
0.375A
0.25A
0.20A
FUSE PRE-ARC JOULE INTEGRALS
VS. PRE-ARC TIME FOR SIZE 1206 (TYPICAL)
28
Accu-Guard®
SMD Thin-Film Fuse
QUALITY & RELIABILITY
Accu-Guard®series of fuses is based on established
thin-film technology and materials used in the semiconduc-
tor in dus try.
• In-line Process Control: This program forms an integral
part of the production cycle and acts as a feedback sys-
tem 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 pro ce dures and equip ment. These mea sures 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
char ac ter is tics. Each production lot is 100% evaluated for
electrical resistance. In addition, each production lot is
eval u at ed on a sample basis for:
• Insulation resistance (post fusing)
• Blow time for 2 x rated current
• Endurance test: 125°C, rated current, 4 hours
HANDLING AND SOLDERING
SMD chips should be handled with care to avoid dam age
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
All flexible types of circuit boards may be used
(e.g. FR-4, G-10).
For other circuit board materials, please consult factory.
COMPONENT PAD DESIGN
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 per mis si ble to
decrease this to as low as 85% of component width but
it is not advisable to go be low this.
b. Pad overlap 0.5mm.
c. Pad extension 0.5mm for reflow. Pad ex ten sion about
1.0mm for wave soldering.
PREHEAT & SOLDERING
The rate of preheat in production should not exceed
4°C/second. It is recommended not to exceed 2°C/
sec ond.
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 tem per a -
ture controlled model not exceeding 30 watts should be
used and set to not more than 260°C. Max i mum al lowed
time at tem per a ture is 1 minute.
COOLING
After soldering, the assembly should preferably be al lowed
to cool naturally. In the event of assisted cool ing, similar
con di tions to those rec om mend ed for pre heat ing should
be used.
REFLOW SOLDERING
Dimensions: millimeters (inches)
0.8
(0.031)
2.3
(0.091) 0.6
(0.024)
0.85
(0.033)
0.85
(0.033)
3.0
(0.118)
1.25
(0.049)
1.0
(0.039)
1.0
(0.039)
1.0
(0.039)
1.0
(0.039)
1.0
(0.039)
2.0
(0.079)
4.0
(0.157)
1.6
(0.063)
WAVE SOLDERING
Dimensions: millimeters (inches)
3.1
(0.122)
0.8
(0.031)
0.6
(0.024)
1.25
(0.049)
1.25
(0.049)
1.5
(0.059)
1.5
(0.059)
2.0
(0.079)
5.0
(0.197)
1.6
(0.063)
1.25
(0.049)
0.6 (0.024)
1.25
(0.049)
3.1
(0.122)
3.1
(0.122)
0.85
(0.033)
0.6 (0.024)
0.85
(0.033)
2.3
(0.091)
3.1
(0.122)
1206
0612
0805
0603
0402 0402
1206
0612
0805
0603
0
.
8
(
0.031
)
0
.
8
(
0.031
)
0
.
5
(
0.020
)
2.1
(
0.083
)
0
.
59
(
0.023
)
0
.
6
(
0.024
)
0
.
6
(
0.024
)
0
.
5
(
0.020
)
1.7
(
0.068
)
0
.
59
(0.023)
Accu-Guard®
SMD Thin-Film Fuse
RECOMMENDED SOLDERING PROFILES
IR REFLOW
CLEANING RECOMMENDATIONS
Care should be taken to ensure that the devices are thor-
oughly cleaned of flux residues, especially the space
beneath the device. Such residues may oth er wise 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, acetylace-
tone, water, and other stan-
dard PCB cleaning liquids.
Ultrasonic conditions . . . .power – 20w/liter max. fre-
quency – 20kHz to 45kHz.
Temperature . . . . . . . . . .80°C maximum (if not other-
wise limited by chosen solvent
system).
Time . . . . . . . . . . . . . . . .5 minutes max.
STORAGE CONDITIONS
Recommended storage conditions for Accu-Guard®
prior to use are as follows:
Temperature 15°C to 35°C
Humidity ≤65%
Air Pressure 860mbar to 1060mbar
VAPOR PHASE
220
210
200
190
180
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
00.511.522.533.544.5
Assembly enters the
preheat zone
Additional soak time
to allow uniform
heating of the
substrate
Soak time
1) Activates the flux
2) Allows center of board
temperatures to catch up with
corners
45-60 sec.
above solder
melting point
Assembly exits heat–
no forced cooldown
186°C solder melting
temperature
COMPONENT LAND TEMP (DEG C)
Time (mins)
0
20
TEMPERATURE °C
40
60
80
100
120
140
160
180
200
215°C
Time (minutes)
Preheat
Transfer from
preheat with
min. delay &
temp. loss
0
20
40
60
80
100
120
140
160
180
215°C
Time (seconds)
Reflow
Enter
Vapor
Natural
Cooling
Duration varies
with thermal mass
of assembly
10–60 secs typical
10 20 30 40 50 60 70
200
0 20 30 40 50 60 70 80 90 100 110 120
260
240
220
200
180
160
140
120
100
80
60
40
20 Time (seconds)
Enter Wave
Natural
Cooling
100°C
3–5 seconds
10
TEMPERATURE °C
WAVE SOLDERING
30
Accu-Guard®
SMD Thin-Film Fuse
Note: AVX reserves the right to change the information published herein without notice.
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)
A(1) B* C D* E F G
180 + 1.0 1.5 min. 13 ± 0.2 20.2 min. 50 min. 9.4 ± 1.5 14.4 max.
(7.087 + 0.039) (0.059 min.) (0.512 ± 0.008) (0.795 min.) (1.969 min.) (0.370 ± 0.050) (0.567 max.)
Metric dimensions will govern.
Inch measurements rounded for reference only.
(1) 330mm (13 inch) reels are available.
REEL DIMENSIONS: millimeters (inches)
ABCDE F
8.0 ± 0.3 3.5 ± 0.05 1.75 ± 0.1 2.0 ± 0.05 4.0 ± 0.1 1.5
(0.315 ± 0.012) (0.138 ± 0.002) (0.069 ± 0.004) (0.079 ± 0.002) (0.157 ± 0.004) (0.059 )
Note: The nominal dimensions of the component compartment (W,L) are derived from the component size.
CARRIER DIMENSIONS: millimeters (inches)
FULL RADIUS
D*
B* C
E
F
G MAX.
A
DRIVE SPOKES OPTIONAL
IF USED, ASTERISKED
DIMENSIONS APPLY.
*
A
E
P
D
F
W
L
C
B
10 PITCHES
CUMULATIVE
TOLERANCE ON
TAPE ±0.2
CENTER LINES
OF CAVITY
TOP
TAPE
DIRECTION OF FEED
P = 4mm except 0402 where P = 2mm
+0.1
-0.0
+0.004
-0.000
Accu-Guard®
SMD Thin-Film Fuse
Correct choice of an Accu-Guard®fuse for a given applica-
tion is fairly straightforward. The factor of pre-arc I2t, howev-
er, 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 tempera-
ture range of -55°C to +125°C. Note, how ev er, that fusing
current is sensitive to temperature. This means that the fuse
must be derated or uprated at circuit temperatures other
than 25°C:
2. Circuit Voltage
Maximum Voltage: Accu-Guard®is specified for circuits of
up to rated voltage. Accu-Guard®will suc cess ful ly 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 pre-
vent 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 ter mi na tions.
4. Steady-State Current
The Accu-Guard®current rating is based on IEC Spec i fi ca -
tion 127-3. In accordance with this in ter na tion al 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 sub-
ject 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 puls-
es may be so large that they are the determining factor for
choosing the Accu-Guard®current rating; not necessarily
steady state cur rent.
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 IRwill 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 Accu-
Guard®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 char ac ter ized;
I2t-t and I2t-I graphs are in this catalog. The prob lem is cal-
culating the I2t of the circuit current pulses. This concept is
not familiar to most engineers. Correct calculation of pulse
Joule integral and sub se quent choice of Accu-Guard®
current rating is il lus trat ed by way of the attached examples.
HOW TO CHOOSE THE CORRECT ACCU-GUARD®FUSE
FOR CIRCUIT PROTECTION
Environmental
Accu-Guard®
Temperature
Current Carrying Capacity*
F0402E, F0805B, F1206A, F0805B 2.50A
F0603C F0612D
F0603E F1206B & 3.00A
-55°C to -11°C 1.07 x IR1.07 x IR1.07 x IR1.07 x IR1.07 x IR
-10°C to 60°C IRIRIRIRIR
61°C to 100°C 0.85 x IR0.93 x IR0.90 x IR0.90 x IR0.80 x IR
101°C to 125°C 0.80 x IR0.90 x IR0.90 x IR0.75 x IR0.75 x IR
*As a function of nominal rated current, IR.
32
Fig. 2c. Choice of 0.75A fuse, example #2.
Pre-arcing I2t
Maximum I2t design rule
I2t for sample switch-on pulse
Accu-Guard®
SMD Thin-Film Fuse
t
l max.
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)2x 7.7 x 10-6 sec]/2 = 8.9 x 10-5 A2sec.
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 inte-
gral within 7.7 μsec without actuation. Ac cord ing 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.
FUSE PRE-ARCING JOULE INTEGRALS
vs. PRE-ARCING TIME
2. Triangular current pulse
The Joule integral for triangular pulse is
[(Imax.)2x t]/3,
see Fig. 2a.
Fig. 2a. Triangular pulse parameters for Joule
integral calculation, example #2.
t
l max.
Thus, for the current pulse in Figure 2b, the Joule integral is
[(1.5A)2x 3 x 10-3 sec]/3 = 2.25 x 10-3 A2sec.
Fig. 1b. Sine wave pulse, example #1. Fig. 2b. Triangular pulse, example #2.
The pulse duration is 3 msec. In the I2t graph on page 6, pre-
arcing 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
0.75A
PRE-ARCING TIME l2t, A2 sec
PRE-ARCING TIME, sec
100
10
1
10-1
10-2
10-3
10-4
10-5
10-7 10-6 10-5 10-4 10-3 10-2 10-1 110
x
X
10 μsec/div
1A/div
2 msec/div
0.5A/div
0.5A
PRE-ARCING TIME l2t, A2 sec
PRE-ARCING TIME, sec
100
10
1
10-1
10-2
10-3
10-4
10-5
10-7 10-6 10-5 10-4 10-3 10-2 10-1 110
x
X
Fig. 1c. Choice of 0.5A fuse, example #1.
Pre-arcing I2t
Maximum I2t design rule
I2t for sample current pulse
DESIGNING FOR CURRENT
PULSE SITUATIONS
1. Sine wave current pulse
The Joule integral for sine wave pulse is
[(Imax.)2x t]/2,
see Fig. 1a.
Accu-Guard®
SMD Thin-Film Fuse
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.
Fig. 3a. Trapezoidal pulse parameters for Joule
integral calculation, example #3.
4. Lightning strike
A lightning strike pulse is shown in Figure 4a. After an initial
linear rise, the current declines exponentially.
3. Trapezoidal current pulse
The Joule integral for a trapezoidal pulse is
[(Imin.)2+ Imin. x (Imax. - Imin.) + (Imax-Imin)2]x t,
3
see Fig. 3a.
t
l min.
l max.
0.5 msec/div
0.5A/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
0.50A
PRE-ARCING TIME l2t, A2 sec
PRE-ARCING TIME, sec
100
10
1
10-1
10-2
10-3
10-4
10-5
10-7 10-6 10-5 10-4 10-3 10-2 10-1 110
x
Fig. 3c. Choice of 0.5A fuse, example #3.
Pre-arcing I2t
Maximum I2t design rule
I2t for sample switch-on pulse
X
X
DESIGNING FOR CURRENT PULSE SITUATIONS (CONT.)
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.2x 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)2x 2 x 10-6sec/3+0.72 x (25A)2x 10 x 10-6sec = 4.92 x 10-3A2sec.
t0.5
0.51 max.
l max.
Fig. 4a. Lightning pulse parameters for Joule
integral cal cu la tion, example #4.
10 μsec/div
5A/div
Fig. 4b. Lightning strike pulse, example #4.
For practical calculations, the duration of ex po nen tial 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.
FUSE PRE-ARCING JOULE INTEGRALS
vs. PRE-ARCING TIME
Fig. 4c. Choice of 0.5A fuse, example #4.
Pre-arcing I2t
Maximum I2t design rule
I2t for sample switch-on pulse
1.25A
PRE-ARCING TIME l2t, A2 sec
PRE-ARCING TIME, sec
100
10
1
10-1
10-2
10-3
10-4
10-5
10-7 10-6 10-5 10-4 10-3 10-2 10-1 110
x
3
Fig. 6b. Choice of 0.75A fuse, example #6.
Pre-arcing I2t
Maximum I2t design rule
I2t for sample switch-on pulse
Fig. 5b. Choice of fuse, example #5.
Pre-arcing I2t
Maximum I2t design rule
I2t for sample switch-on pulse
Accu-Guard®
SMD Thin-Film Fuse
6. Switch-on pulse and steady-state current
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.
5. Complex current pulse
If the pulse consists of several waveforms, all of them should
be evaluated sep a rate ly, and then the total Joule integral
should be calculated as well.
2 msec/div
0.5A/div
Fig. 6a. Switch-on pulse and steady-state current,
example #6.
200 μsec/div
2A/div
Fig. 5a. Complex pulse, example #5.
0.75A
PRE-ARCING TIME l2t, A2 sec
PRE-ARCING TIME, sec
100
10
1
10-1
10-2
10-3
10-4
10-5
10-7 10-6 10-5 10-4 10-3 10-2 10-1 110
xx
X
FUSE PRE-ARCING JOULE INTEGRALS
vs. PRE-ARCING TIME
The Joule integral for the second triangle is
[(5.33A)2x 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.
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
0.75A
PRE-ARCING TIME l2t, A2 sec
PRE-ARCING TIME, sec
100
10
1
10-1
10-2
10-3
10-4
10-5
10-7 10-6 10-5 10-4 10-3 10-2 10-1 110
x
X
The steady-state current is 0.5A, and 1A fuse is typically rec-
ommended to meet the steady-state con di tion. Based on
steady-state current, the 1A fuse should be chosen for this
application.
DESIGNING FOR CURRENT PULSE SITUATIONS (CONT.)
34