Littelfuse 437 Series - Manual (Page 2)

© 2013 Littelfuse, Inc.
Specifications are subject to change without notice.
Revised: 12/19/13
Surface Mount Fuses
Ceramic Fuse > 437 Series
Average Time Current Curves
0.001
0.01
0.1
1
10
100
0.1 1 10 100
CURRENT IN AMPERES
TIME IN
SE
CO
ND
S
.2
50
A
.3
75
A
.50
0A
.750A 1A 2A 7A 1.25 1.5A 1.75 2.5A 3A 3.5A 4A 5A 8A
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 Rerating Curve
40
60
80
100
120
140
-65 -45 -25 -5 15 35 55 75 95 115 135 155
TEMPERATURE (°C)
PE
RC
EN
T
OF
RA
TI
NG
Time
Te
mperatur
e
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. Rerating depicted in this curve is in addition to the standard rerating of 20% for
continuous operation.
Wave Soldering 260°C, 10 seconds max.