Application information SMP100MC
6/13 Doc ID 9699 Rev 5
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 circuits opening. Lightning surge and
mains disturbance surges are defined by standards like GR1089, TIA/EIA IS-968,
ITU-T K20.
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)
Z/R
th(j-a) th(j-a)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03
tp(s)
Printed circuit board - FR4,
copper thickness = 35µm,
recommended pad layout
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1 10 100 1000
V (V)
R
C [V ] / C [V =2V]
RR
F =1MHz
V = 1V
Tj = 25°C
OSC RMS
Line
Protection stage
Protection stage
Ring
relay
Line
Ex. Analog line card Ex. ADSL line card or terminal
