SI99-03
Surging Ideas
TVS Diode Application Note
PROTECTION PRODUCTS
Lightning Immunity Requirements of
Test Connecti-
Open
Circuit
Voltage
(V)
Short
Number Added Accept-
ITU-T K.20 and K.21
#
on
Circuit of Tests Prote-
Current (Note 2)
(A)
ance
Figure 1
ction
None
None
None
Criteria
The Telecommunication Standardization Sector of the
International Telecommunication Union (ITU-T) has
developed fundamental testing methods to help
predict the survivability of network and customer
based switching equipment to various environmental
conditions. These standards are recognized in many
places throughout Europe and the Far East.
1
2
3
A and E
1000
25
10
10
10
A
A
A
B earthed 10x700µs 5x310µs
B and E
1000
25
A earthed 10x700µs 5x310µs
A+B
1000
50
and E
10x700µs 5x310µs
(Note 1)
ITU-T K.20 and K.21 are the two ITU-T standards
applicable for most telecommunication equipment to
be connected to the network. ITU-T K.20 primarily
focus on switching equipment powered by the central
office, while ITU-T K.21 focus on customer premise
equipment. Although both standards also contains
requirements and testing methods for power induction
and power contact, this application note will only focus
on the lightning immunity requirement portion.
4
5
6
A and E
4000
100
10
10
10
Primary
Primary
Primary
A
A
A
B earthed 10x700µs 5x310µs
B and E
4000
100
A earthed 10x700µs 5x310µs
A+B
and E
4000
200
10x700µs 5x310µs
(Note 1)
Table 1 - ITU-T K.20 Lightning Simulation
ITU-T K.20 covers telephone exchanges and switching
centers. There are two levels to ITU-T K.20, a lower
and a higher level. The equipment has to only meet
one of the two levels in order to be compliant under
the K.20. The equipment that is used in an unexposed
environment is covered in the lower level. Unexposed
environment is where over-voltage and over currents
are expected to be small and external protectors are
not necessary. Equipment that is used in a more
exposed environment is covered in the higher level.
More exposed environment is where over-voltage and
over-current are higher and external line protectors are
necessary. Guidelines for determining which environ-
ment the equipment falls under can be found in ITU-T
K.11. Figure 1 shows the test connection block
diagram for the ITU-T K.20 lightning simulation. Table 1
lists the ITU-T K.20 lightning simulation test.
Notes:
1. This is a simultaneous surge. The specified current is the
resultant current (sum of terminal A and terminal B) with respect to
ground (terminal E).
2. The time interval between multiple applications should be 1
minute. In the case of pulse tests, the polarity should be reversed
between consecutive pulses.
3. All other terminals are connected to earth ground.
Test Connecti-
Open
Circuit
Voltage
(V)
Short
Circuit
Current (Note 2)
(A)
Number Added Accept-
#
on
Figure 1
of Tests
Prote-
ction
ance
Criteria
1
2
3
T1 and A
T2 and B 10x700µs 5x310µs
1500
75
10
10
10
None
Primary
None
A
A
A
T1 and A
T2 and B 10x700µs 5x310µs
4000
200
T1 and A
(Note 3)
1000
25
10x700µs 5x310µs
ITU-T K.21 covers desk-borne equipment. The equip-
ment can be in an exposed or unexposed environment.
The standard assumes that equipment in exposed
environment has external line protectors installed and
equipment in unexposed environment has none. This
means that testing under the ITU-T K.21 standard is
conducted with and without external line protectors.
Figure 2 shows the test connection block diagram for
the ITU-T K.21 lightning simulation. Table 2 lists the
ITU-T K.21 lightning simulation test.
(Note 1)
4
5
6
T1 and B
(Note 3)
1000
25
10
10
10
None
Primary
Primary
A
A
A
10x700µs 5x310µs
T1 and A
(Note 3)
4000
100
10x700µs 5x310µs
T1 and B
(Note 3)
4000
100
10x700µs 5x310µs
(Note 1)
Table 2 - ITU-T K.21 Lightning Simulation
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