This application note will explain the different PoE options and give guidance on EMI prevention techniques.

Transcription

1 Introduction In HDBaseT applications, you have the option of adding Power over Ethernet (PoE). But because of the very fast transmission rates used; special care has to be taken to minimise the effect of any noise generated from the PoE affecting the data. This application note will explain the different PoE options and give guidance on EMI prevention techniques. PoE Options The HDBaseT Alliance has written a Power over HDBaseT (PoH) specification, which in essence is an extension on the PoE specification IEEE0.at. The PoH specification now allows the Power Sourcing Equipment (PSE) to use all four pairs to transmit power (within the Cate or Cat cable). Were as the IEEE0.at specification only allows power to be transmitted over two pairs. In addition to using all four pairs, the PoH specification allows the PSE to transmit up to 9W, which opens up a wider range of application. But the PoH specification is also backwards compatible with IEEE0.at to allow for lower power applications. PoH Solution Figure shows a block diagram for a PoH solution using the Valens Play circuit. 0GBASE-T PSE RJ TX - Play Cct RX Play Cct STATUS OUT Isolated VIN V PSU Ag00 (0W), J VIN Ag00 D J VDC, C 000µF, OUT, Figure : PoH Application Drawing Page of ANX-POE-HDBaseT-v-

2 The Ag00 module shown in the PSE in Figure does not have a dc/dc converter, so will not add any noise to the TX Play circuit. The Isolated PSU supplying power to the Ag00 may need to have a filtering, but this will depend on its performance. The Ag00 module shown in the in Figure does have an on-board dc/dc converter, so will need some input filtering to prevent any noise this generates from affecting the signal to the RX Play circuit. From the tests that we have conducted one simple and inexpensive approach is to connect three MPZ0S0A (TDK) ferrite chip beads in series with each centre tap. These ferrite chip beads are quite small (00 package) and only cost ~$0.0 (USD) each; Figure shows this configuration (L to L). RX Play Cct L L L L L L L L L9 J, VIN Ag00 J, C VDC 000µF D,, L0 L L Figure : PoH with Ferrite Chip Beads Page of ANX-POE-HDBaseT-v-

3 If noise continues to be an issue, even with the ferrite chip beads in series with each centre tap. The addition of a V capacitor filter will reduce the noise further, see Figure. RX Play Cct L L L L L L L L L9 J, VIN Ag00 J, C VDC 000µF D,, L0 L L C C Figure : PoH with Ferrite Chip Beads and V Capacitor Filter C and C can be.nf to 0nF. Because these capacitors cross the isolation barrier, they will need to be capable of handling the 0dc impulse test. Page of ANX-POE-HDBaseT-v-

4 PoE Solution The following shows how the same techniques used for PoH can be implemented with IEEE0.at Type and Type (IEEE0.af) modules. In Figure and the ferrite chip beads can be MPZ0S0A for IEEE0.at Type applications and MMZ0S0A for Type (IEEE0.af) applications. RX Play Cct L L L VIN VDC Module* C 0µF D -VDC L L L C C * Module without internal bridge rectifiers Figure : PoE Solution for Module without Internal Bridge Rectifiers C and C can be.nf to 0nF. Because these capacitors cross the isolation barrier, they will need to be capable of handling the 0dc impulse test. Page of ANX-POE-HDBaseT-v-

5 RX Play Cct L L L L L L L L L9 D VA Module* VA VDC VB C 0µF -VDC D VB L0 L L C C C C * Module with internal bridge rectifiers Figure : PoE Solution for Module with Internal Bridge Rectifiers C to C can be.nf to 0nF. Because these capacitors cross the isolation barrier, they will need to be capable of handling the 0dc impulse test. Comments The techniques detailed in this application note have been shown to reduce noise that can affect the performance of HDBaseT. Page of ANX-POE-HDBaseT-v-