Introduction to Circuit Protection

Introduction to Circuit Protection

Transientology

2

© 2009 Littelfuse, Inc.

Specifications are subject to change without notice.

Surface Mount Fuses

Please refer to www.littelfuse.com/series/440.html for current information.

440 Series

Ceramic Fuse > 440 Series

Average Time Current Curves

0.001

0.1

1.0

10.0

100.0

1000.

0.01

0.1

1

10

100

CURRENT IN AMPERES

reflow condition

Pb-freeassembly

pre Heat

-Temperature min (T

150°C

-Temperature max (T

200°C

-Time (min to max) (t

60 – 180 seconds

Average ramp-up rate (liquidusTemp

(T

3°C/second max.

T

5°C/second max.

reflow

-Temperature (T

217°C

-Temperature (t

60 – 150 seconds

peakTemperature (T

Time within 5°c of actual peak

Temperature (t

10 – 30 seconds

ramp-down rate

6°C/second max.

Time 25°c to peakTemperature (T

8 minutes max.

Do not exceed

260°C

Soldering Parameters

Temperature Derating Curve

40

60

80

100

120

140

-65

-45

-25

-5

15

35

55

75

95

115

135 155

TEMPERATURE (°C)

Time

25

time to peak temperature

(t 25ºC to peak)

Ramp-down

Ramp-up

Preheat

Critical Zone

Example:

For continuous operation at 75 degrees celsius, the fuse should be derated as follows:

I = (0.80)(0.85)I

Note:

1. Derating depicted in this curve is in addition to the standard derating of 20% for

continuous operation.

Wave Soldering

260°C, 10 seconds max.