This document describes a simplified SPICE behavioral model for simulating fuse behavior. The model allows users to set parameters like current rating, fusing factor, internal resistance, and melting value based on datasheet specifications. Simulation results show fusing time varies with DC current level and different current waveforms based on I2t heating effects. A specific fuse model tailored for a part provides more accurate fusing time predictions than the general model.

1. Fuse
Simplified SPICE Behavioral Model
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2. Contents
1.Benefit of the Model
2.Model Feature
3.Parameter Settings
4.Fuse Specification (Example)
5.Fusing Time vs. DC Current
6.Fusing Time vs. Current Pattern
7.Specific Fuse Model
Simulation Index
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3. 1. Benefit of the Model
• Easily create your own fuse models by setting a few
parameters, that’s usually provided by the
manufacturer’s datasheet.
• Enables circuit designer to safely test and optimize their
circuit protection design, and to predict component and
circuit stress under extreme conditions (e.g. at the fuse
blow).
• The model is optimized to reduce the convergence error.
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4. 2. Model Feature
The model accounts for: 10
• Current Rating
• Fuse Factor 1
Fusing Time (Sec.)
• Internal Resistance
0.1
• Normal Melting I2t
Enable the model to simulate fusing time
(blow time) as a function of I2t. 0.01
The model can be used for testing the 0.001
blow time for the different current pattern. 0.1 1 10 100
Fusing Current (A)
A one-shot switch, once fuse is opened it
cannot be closed. Fig.1 Fusing Time vs. Fusing Current Characteristic
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5. 3. Parameter Settings
• From the fuse specification, the model is characterized by setting parameters Irate, FF,
Rint and I2t.
Model Parameters:
U1 Irate = the current rating of fuse [A]
FF = Fusing Factor, the ratio of the
minimum fusing current (the current
FUSE that fuse start to heat up) to Irate.
(e.g. Irate =400mA and the minimum
IRATE = 400m fusing current is 620mA then FF =
FF = 1.55 620m/400m = 1.55)
RINT = 650m Rint = internal resistance of fuse
I2T = 0.024
I2t = Normal Melting value [A2, seconds]
Fig.2 Fuse model with default parameters
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6. 4. Fuse Specification (Example)
10
Current Internal I2t (A2, the minimum fusing current
Part No. Rating R. max. seconds is 620mA, FF = 20m/400m
= 1.55
(mA) (m) ) 1
Fusing Time (Sec.)
CCF1N0.4 400 650 0.024
0.1
U1
0.01
FUSE
IRATE = 400m
FF = 1.55 0.001
RINT = 650m 0.1 1 10 100
I2T = 0.024 Fusing Current (A)
Fig.3 Shows the complete setting of fuse model parameters by using data from the
datasheet of CCF1N0.4 provided by KOA Speer Electronics, Inc.
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7. 5. Fusing Time vs. DC Current
Simulation Result Simulation Circuit
10A
PARAMETERS:
(960.962u,5.0000) dc_current = 1
sense
U1
tF = 960.962usec. at IF = 5A FUSE
I1 IRATE = 400m
(6.0051m,2.0000) I1 = 0 FF = 1.55 RL
I2 = {dc_current} RINT = 650m 1
tF = 6.0051msec. at IF = 2A I2T = 0.024
T1 = 0
(24.013m,1.0000) T2 = 100n
1.0A
tF = 24.013msec. at IF = 1A 0 0
*Analysis directives:
.TRAN 0 1s 500u 100u
.STEP PARAM dc_current LIST 1, 2, 5
100mA
1.0ms 10ms 100ms 1.0s
I(sense)
Time
• The simulation result shows the fusing times, tF, (the time that fuse blows) at
the different fuse currents, IF .
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8. 5. Fusing Time vs. DC Current
Comparison Graph
10
Measurement
Simulation
1
Fusing Time (Sec.)
0.1
0.01
0.001
0.1 1 10 100
Fusing Current
Graph shows the comparison result between the simulation result vs. the
measurement data. The fusing current error (average from 0.001-10 sec.) = 4.9%
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9. 6 Fusing Time vs. Current Pattern
Simulation Result Simulation Circuit
2.0A
sense1
U1
1.5A tF = 149.796msec. for triangle wave
FUSE
I1 IRATE = 400m
(149.796m,959.222m) IOFF = 0 FF = 1.55 RL1
RINT = 650m 1
1.0A FREQ = 50
I2T = 0.024
IAMPL = 1
PHASE = -90
0 0
0.5A
sense2
U2
0A
FUSE
I2 IRATE = 400m
-0.5A TD = 0 FF = 1.55 RL2
TF = 10m RINT = 650m 1
I2T = 0.024
PW = 0
-1.0A PER = 20m
0 I1 = -1 0
I2 = 1
(59.503m,-987.814m) TR = 10m
-1.5A
tF = 59.503msec. for sine wave
-2.0A .TRAN 0 0.2s 0 100u
0s 20ms 40ms 60ms 80ms 100ms 140ms 180ms
I(sense1) I(sense2)
Time
• The simulation result shows the fusing times, tF, (the time that fuse blows)
for the same peak current but different in current patterns(waveforms).
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10. 7. Specific Fuse Model
Comparison Graph
10
Measurement
Simulation
U1 1
Error reduce
to 0.4%
Fusing Time (Sec.)
CCF1N0_4 0.1
Model of fuse part number 0.01
CCF10.4, all parameters and
function are already set
0.001
0.1 1 10 100
Fusing Current
If the most accurate result is required, we could provide the specific model that
optimized for each part number of fuse. The fusing current error (average from 0.001-
10 sec.) will reduce from 4.9% (simplified model) to 0.4% (specific fuse model)
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11. Simulation Index
Simulations Folder name
1. Fusing Time vs. DC Current.................................. DC
2. Fusing Time vs. Current Pattern............................ Pattern
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