Design for PD System Surge Immunity PD701xx/ PD701xx APPLICATION NOTES
■This document provides detailed design guidelines to sustaining high voltage or current surges per typical immunity requirements in PoE PD systems using Microchip controllers PD701xx and PD702xx, as well as active diode bridge PD70224.
●Immunity Requirements:
■Various agencies around the world define different surge voltage levels, source impedance, and maximum surge current. This application note provides information on IEC/EN 61000-4-5 (2014 Ed.3), ITU-T K21 (2019 Ed.), and GR-1089, which are the most common surge immunity standards in PoE PD systems.
■The IEC 61000-4-5 (Par. 6.3.3.3) states that due to the nature of unshielded wiring, coupling to symmetrical interconnection lines (twisted pairs) is always in common mode, that is, between all lines to ground. However, ITU-TK.21 and GR-1089 specify for unshielded PoE lines a differential mode surge as well. Currently, IEEE 802.3 does not define the PoE surge requirements, so it is up to you to choose the standard that is the best fit for your application.
■For indoor applications, IEC 61000 4-5 specifies 1.2/50 μs–8/20 μs common mode surge waveform with voltage level 0.5 kV to 2.0 kV, depending on installation class. However, few may choose meeting higher levels of protection, such as 4 kV, which are suitable for outdoors.
■Common mode surge protection requires voltage limiting components that bridge the insulation between PoE domain and earth ground. The IEC/UL 60950-1 (Par.5.2.2) states that these limiters should be disconnected for insulation testing. Apart from this clause, subclause 6.1.2.1 of these standards specifies minimum rated operated voltage of these limiters as a function of AC mains supply in the area where the equipment is installed, unless the equipment qualifies for 6.1.2.2 exclusions. For a worldwide application, this requires minimum operation voltage of the surge protectors over their expected life to be at least 360 V. Similarly, ITU-T now requires 500 Vᴅｃ insulation test without removing any voltage limiters to verify the insulation is still good after the surge tests. For these reasons, voltage limiting devices rated 500 VDC or above are used in our common mode surge tests. A 100 m CAT5 cable is used as a decoupling network.
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PD701xx 、 PD70100 、 PD70101 、 PD70200 、 PD70201 、 PD702 10/A 、 PD70211 、 PD70224 、 PD702xx |
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Application note & Design Guide |
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Please see the document for details |
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English Chinese Chinese and English Japanese |
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03/2020 |
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Revision B |
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DS00003410B;AN3410 |
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241 KB |
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