Application information SMP100LC
6/13 Doc ID 7050 Rev 14
2 Application information
In wire line applications, analog or digital, both central office and subscriber sides have to be
protected. This function is assumed by a combined series / parallel protection stage.
Figure 10. Examples of protection stages for line cards
In such a stage, parallel function is assumed by one or several Trisil, and is used to protect
against short duration surge (lightning). During this kind of surges the Trisil limits the voltage
across the device to be protected at its break over value and then fires. The fuse assumes
the series function, and is used to protect the module against long duration or very high
current mains disturbances (50/60Hz). It acts by safe circuit opening. Lightning surge and
mains disturbance surges are defined by standards like GR1089, TIA/EIA IS-968,
ITU-T K20.
Figure 11. Typical circuits
Figure 8. Variation of thermal impedance
junction to ambient versus pulse
duration
Figure 9. Relative variation of junction
capacitance versus reverse voltage
applied (typical values)
1E-3 1E-2 1E-1 1E+0 1E+1 1E+2 5E+2
0.01
0.1
1
t (s)
p
Z/R
th(j-a) th(j-a)
Printed circuit board - FR4,
copper thickness = 35µm,
recommended pad layout
C [V ] / C [V =2V]
RR
12
5 10 20 50 100 300
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
V (V)
R
F =1MHz
V = 1V
T = 25°C
j
RMS
Line
Protection stage
Protection stage
Ring
relay
Line
Ex. Analog line card Ex. xDSL line card or terminal
Fuse TCP 1.25A
T1
T2
SMP100LC-xxx
Typical circuit for subscriber side
Fuse TCP 1.25A
Tip S
Gnd
SMP100LC-xxx
Ring S
SMP100LC-xxx
Fuse TCP 1.25A
Tip L
Gnd
Ring L
Typical circuit for central office side
