Surface Mount Fuses
Introduction to Circuit Protection
Transientology
Ceramic Fuse > 437 Series
Temperature Rerating Curve
Average Time Current Curves
.375A
.500A
.250A
.750A
1A
1.25
1.5A
1.75
2A
2.5A
3A
3.5A
4A
5A
140
100
PERCENT OF RATING
120
100
10
80
TIME IN SECONDS
60
1
40
-65
-45
-25
-5
15
35
55
75
95
115
135
155
TEMPERATURE (°C)
0.1
Note:
1. Rerating depicted in this curve is in addition to the standard rerating of 20% for
continuous operation.
Example:
For continuous operation at 75 degrees celsius, the fuse should be rerated as follows:
I = (0.80)(0.85)I
RAT
= (0.68)I
RAT
0.01
0.001
0.1
1
10
100
CURRENT IN AMPERES
Soldering Parameters
reflow condition
- Temperature min (T
s(min)
)
pre Heat
- Temperature max (T
s(max)
)
- Time (min to max) (t
s
)
Average ramp-up rate (liquidus Temp
(T
l
) to peak)
T
S(max)
to T
l
- ramp-up rate
reflow
- Temperature (T
l
) (liquidus)
- Temperature (t
l
)
Pb – free assembly
150°C
60 – 180 seconds
3°C/second max.
5°C/second max.
217°C
60 – 150 seconds
260
+0/-5
T
P
T
L
Temperature
7A
8A
t
P
Ramp-up
Critical Zone
T
L
to T
P
200°C
T
S(max)
T
S(min)
Preheat
t
L
Ramp-down
t
S
time to peak temperature
(t 25ºC to peak)
25
Time
peak Temperature (T
p
)
Time within 5°c of actual peak
Temperature (t
p
)
ramp-down rate
Time 25°c to peak Temperature (T
p
)
Do not exceed
°C
10 – 30 seconds
6°C/second max.
8 minutes max.
260°C
Wave Soldering
260°C, 10 seconds max.
437 Series
18
© 2009 Littelfuse, Inc.
Specifications are subject to change without notice.
Please refer to www.littelfuse.com/series/437.html for current information.
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