SI99-03 Surging Ideas TVS Diode Application Note PROTECTION PRODUCTS Lightning Immunity Requirements of ITU-T K.20 and K.21 Test # Connection Figure 1 Open Circuit Voltage ( V) Short Circuit Current (A) Number of Tests (Note 2) Ad d e d Pr o te ction Acceptance Criteria 1 A and E B ear thed 1000 10x700µs 25 5x310µs 10 N one A 2 B and E A ear thed 1000 10x700µs 25 5x310µs 10 N one A 3 A+B and E 1000 10x700µs 50 5x310µs (N ote 1) 10 N one A 4 A and E B ear thed 4000 10x700µs 100 5x310µs 10 Primary A 5 B and E A ear thed 4000 10x700µs 100 5x310µs 10 Primary A 6 A+B and E 4000 10x700µs 200 5x310µs (N ote 1) 10 Primary A 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. 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. Table 1 - ITU-T K.20 Lightning Simulation ITU-T K.20 covers telephone exchanges and switching Notes: centers. There are two levels to ITU-T K.20, a lower 1. This is a simultaneous surge. The specified current is the resultant current (sum of terminal A and terminal B) with respect to and a higher level. The equipment has to only meet ground (terminal E). one of the two levels in order to be compliant under the K.20. The equipment that is used in an unexposed 2. The time interval between multiple applications should be 1 minute. In the case of pulse tests, the polarity should be reversed environment is covered in the lower level. Unexposed between consecutive pulses. environment is where over-voltage and over currents 3. All other terminals are connected to earth ground. are expected to be small and external protectors are Test ConnectiOpen Short Number Added Acceptnot necessary. Equipment that is used in a more # o n C i r c u i t C i r c u i t o f Tests Pr o te ance exposed environment is covered in the higher level. Figure 1 Voltage Current (Note 2) ction Criteria More exposed environment is where over-voltage and ( V) (A) over-current are higher and external line protectors are 1 T1 and A 1500 75 10 N one A necessary. Guidelines for determining which environT 2 a n d B 1 0 x 7 0 0 µs 5 x 3 1 0 µs ment the equipment falls under can be found in ITU-T K.11. Figure 1 shows the test connection block 2 T1 and A 4000 200 10 Primary A diagram for the ITU-T K.20 lightning simulation. Table 1 T2 and B 10x700µs 5x310µs lists the ITU-T K.20 lightning simulation test. ITU-T K.21 covers desk-borne equipment. The equipment 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. 3 T1 and A (N ote 3) 1000 10x700µs 25 5x310µs (N ote 1) 10 N one A 4 T1 and B (N ote 3) 1000 10x700µs 25 5x310µs 10 N one A 5 T1 and A (N ote 3) 4000 10x700µs 100 5x310µs 10 Primary A 6 T1 and B (N ote 3) 4000 10x700µs 100 5x310µs (N ote 1) 10 Primary A Table 2 - ITU-T K.21 Lightning Simulation Revision 9/2000 1 www.semtech.com SI99-03 Surging Ideas TVS Diode Application Note PROTECTION PRODUCTS ITU-T requires that the EUT withstands the lightning test without damage or disturbance and operates properly after the test (Acceptance criteria level A). 25 Ω A Surge Generator Decoupling Element B E A.) Transferred test 25 Ω A Surge Generator Decoupling Element B E Rs=25Ω B.) Longitudinal test Figure 1 - Test Connection Block Diagram for ITU-T K.20 Lightning Simulation Equipment Under Test 25 Ω 15 Ω T2 50 Ω Decoupling Elements T1 Uc 20 µF A A 25 Ω 0.2 µF B B E T3 Figure 2 - Test Condition Block Diagram for ITU-K.21 Lightning Simulation 2000 Semtech Corp. 2 www.semtech.com