Brochure

© 2017 Littelfuse, Inc.
Specifications are subject to change without notice.
Revised: 03/03/17
Surface Mount Fuses
Ceramic Fuse > 437 Series
Average Time Current Curves
.250A
4A
3.5A
3A
2.5A
2A
1.75A
1.5A
1.25A
1A
.500A
.375A
7A
5A
.750A
8A
0.001
0.01
0.1
1
10
TIME IN SECONDS
0.1
1
10 100
CURRENT IN AMPERES
Reflow Condition Pb – free assembly
Pre Heat
- Temperature Min (T
s(min)
) 150°C
- Temperature Max (T
s(max)
) 200°C
- Time (Min to Max) (t
s
) 60 – 180 seconds
Average Ramp-up Rate (Liquidus Temp
(T
L
) to peak)
3°C/second max.
T
S(max)
to T
L
- Ramp-up Rate 5°C/second max.
Reflow
- Temperature (T
L
) (Liquidus) 217°C
- Temperature (t
L
) 60 – 150 seconds
Peak Temperature (T
P
) 260
+0/-5
°C
Time within 5°C of actual peak
Temperature (t
p
)
10 – 30 seconds
Ramp-down Rate 6°C/second max.
Time 25°C to peak Temperature (T
P
) 8 minutes max.
Do not exceed 260°C
Soldering Parameters
Temperature Re-rating Curve
40
60
80
100
120
140
-65 -45 -25 -5 15 35 55 75 95 115 135 155
TEMPERATURE (°C)
PERCENT OF RATING
Time
Temperature
T
P
T
L
T
S(max)
T
S(min)
25
t
P
t
L
t
S
time to peak temperature
(t 25ºC to peak)
Ramp-down
Ramp-up
Preheat
Critical Zone
T
L
to T
P
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
Note:
1. Re-rating depicted in this curve is in addition to the standard re-rating of 20% for
continuous operation.
Wave Soldering 260°C, 10 seconds max.