AN3007 STMICROELECTRONICS | Alldatasheet

Document overview

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Technical content

Datasheet sections

  • 1 Telecom disturbances
  • 4 Board layout recommendation
  • 7 Conclusion
  • 8 Revision history

100 Mbps and Gigabit Ethernet protection

preferred thanks to its lower cost of deployment. called Fast Ethernet), to 1000 Mbps (1000Base-T, called Gigabit Ethernet). Figure 1. Simplified Ethernet network computer is connected to a concentrator, called a hub or server. RJ45 connectors. The max length of this connexion is 100 m.

1 Telecom disturbances

defined in international standards. Figure 2. Line disturbance and protection location internal resistance). Then, the equipment has to withstand a current of 24 A. standard (Table 1), and finally an example of a test setup (Figure 4). Figure 3. Simplified circuit of the combinat ion wave generator (1.2/50 µs - 8/20 µs)

Figure 4. IEC 61000-4-5 - simplified schematic of test setup The IEC 61000-4-5 standard requires five applications of each polarity on the equipment. performance of the equipment after test. contact and 15 kV air discharge. Similarly, Ethernet applications usually recommend the A criterion of IEC 61000-4-2. Table 1. IEC 61000-4-5 surge test levels Table 2. IEC 61000-4-2 test levels

AN3007 100 Mbps and Gigabit Ethernet protection circuits with SLVU2.8 Doc ID 16018 Rev 1 7/20 Note that both SLVU2.8-4A1 and SLVU2.8-8A1 can protect 100 Mbps and Gigabit Ethernet circuits. Figure 6 shows one SLVU2.8-4A1 protecting one 100 Mbps Ethernet port. As the I/Os inside SLVU2.8-4A1 are not internally connected, note that the connections are assumed thanks to PCB tracks running under the SLVU2.8-4A1. One SLVU2.8-8A1 can also be used to protect two 100 Mbps Ethernet ports. Figure 7 shows one SLVU2.8-8A1 protecting one Gigabit Ethernet port. Two SLVU2.8-4A1 can also be used to protect one Gigabit Ethernet port to offer a more convenient layout.

Board layout recommendation AN3007 8/20 Doc ID 16018 Rev 1

4 Board layout recommendation

Board layout must be carefully considered for the suppression of ESD events. Such very fast transients have a very high di/dt, and then the voltage across parasitic inductances located in the protection path may become very important (V = L·di/dt). And finally the device to be protected will see not only the clamping voltage of the SLVU2.8 protection device, but also this high overvoltage. Hence, we recommend the following layout considerations for an optimized protection:

  • Put the SLVU2.8 protection device as close as possible to the RJ45 connector to reduce the transient coupling in nearby lines.
  • Minimize the track length between the SLVU2.8 protection device and the line to be protected.
  • Place ground planes wherever possible.

waveform instead of 8 / 20 µs. Both devices have been designed for this purpose. Figure 12. +8 kV contact discharge test applied to SLVU2.8-4A1 Figure 13. -8 kV contact discharge test applied to SLVU2.8-4A1

50 V/div

Figure 14. +15 kV air discharge test applied to SLVU2.8-4A1 Figure 15. -15 kV air discharge test applied to SLVU2.8-4A1 ESD tests have been performed with Schaffner NSG438 ESD generator.

5 V/div

a duration less than one nanosecond and then about a few volts. few nanoseconds and then about a few volts. Figure 16. +8 kV contact discharge test applied to SLVU2.8-8A1 Figure 17. -8 kV contact discharge test applied to SLVU2.8-8A1

Figure 18. +15 kV air discharge test applied to SLVU2.8-8A1 Figure 19. -15 kV air discharge test applied to SLVU2.8-8A1 a duration less than one nanosecond and then about a few volts. few nanoseconds and then about a few volts.

For SLVU2.8-4A1, Figure 22 shows a differential crosstalk lower than -40 dB up to 3 GHz. Figure 23 shows a differential crosstalk lower than -45 dB up to 3 GHz for SLVU2.8-8A1. Figure 24. Eye diagram with SLVU2.8-4A1 Figure 25. Eye diagram with SLVU2.8-8A1

250 Mbps

Signal integrity with SLVU2.8 AN3007 18/20 Doc ID 16018 Rev 1 Eye diagram measurements have been performed with Agilent 81134A 3.35 GHz pulse / pattern generator, Agilent Infinium DCA-J 86100C digital communication analyzer and Agilent 86112A 20GHz electrical module. Figure 24 and 25 show the eye diagram measurements for SLVU2.8-4A1 and SLVU2.8-8A1. Gigabit Ethernet operates at 250 Mbps (over 4 wire pairs), which corresponds to a bit time of 4 ns. This bit time of 4 ns can be clearly seen on both eye diagram measurements. The IEEE 802.3 standard specifies a signal template for Gigabit Ethernet applications. This identifies a maximum rise time of 1ns when the signal voltage changes from 0.7 V to 1.9 V, and a maximum fall time of 1 ns when the signal voltage changes from 1.9 V to 0.7 V. And on both eye diagram measurements, the rise time and the fall time, which are measured between 10% and 90% of the signal are about 500 ps, which is consistent with IEEE 802.3 standard requirements.

7 Conclusion

Ethernet, are increasingly deployed to speed up the data traffic. preserve signal integrity and do not disturb the normal operation of the system.

8 Revision history

Table 3. Document revision history 30-Mar-2010 1 Initial release.