Network port isolation transformer network cable side protection and routing

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Network port isolation transformer network cable side protection and routing [Copy link]

 

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As shown in the figure above, the upper side is a network port isolation transformer, U43 is a clamping diode, the internal is a rectifier bridge connected to the TVS structure, and the anode of the TVS tube on the chip side is grounded. There is no problem with this connection. The problem is who is the reference "ground" of the two differential pairs on the network cable side? Can it refer to PE (earth)? What should the TVS tube of the protection device U44 on the network cable side be connected to or should it be left floating for differential protection only?

As shown in the picture above, the chip is an isolation transformer. Should it be closer to the interface or the driver chip?

qwqwqw2088

It is better to be closer to the driver chip

The purpose of protection isolation is to consider the impact of EMI

One of the functions of the transformer itself is to isolate

呜呼哀哉

qwqwqw2088 posted on 2022-12-5 14:38 It is better to be close to the driver chip for better protection. The purpose of isolation is to consider the impact of EMI. One of the functions of the transformer itself is also isolation

The key problem is that there is no reference on the side of the transformer close to the network cable. Is the "ground" plane underneath the earth? RJ45 has an isolation transformer inside. I never considered that this connector needs an isolation transformer, so I had the question of the reference plane.

I guess there should really be copper underneath to connect to PE.

qwqwqw2088

It is grounded through C144. Note that this capacitor should be a high-voltage capacitor.

The 75 ohm terminal should be placed close to the TX and RX pins.

qwqwqw2088

You can find some information about the wiring of Bob's circuit, refer to

呜呼哀哉

qwqwqw2088 posted on 2022-12-5 17:20 You can find some information about the wiring of Bob's circuit for reference

BOB Smith's related articles all talk about circuit principles. It seems that the TVS I added on the cable side is superfluous. I'll look for it again to see if anyone has posted a picture.

btty038

How you choose this device should be planned, so pay attention to the key elements on the datasheet. Just meet your design requirements and ensure that the circuit you design can run normally and achieve the expected planning effect.

damiaa

hr911105a hr911102a The documentation seems to say that 75 ohm and 1000pf capacitors are in it.

hr911105a 8-leg chs gnd is connected to the chassis ground (earth).

The reference ground of the signal line from the inside to the phy is gnd

There are many ways to connect GND and chassis ground.

呜呼哀哉

damiaa posted on 2022-12-9 16:20 hr911105a hr911102a The information seems to say that 75 ohm and 1000pf capacitors are in it.

This is the network port of another board I designed. This RJ45 connector comes with an isolation transformer and has the same structure as the picture you sent.

This is a connector without an isolation transformer. The isolation transformer is a bit far from the connector. There is no way around it. The structure is like this. Below the isolation transformer, put the 2*75Ω+1nF/2000V on the bottom layer.

damiaa

Alas, published on 2022-12-9 16:42

Good. Learned.

Some people say: The network cable differential length compensation should be done wherever there is a difference :

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damiaa published on 2022-12-9 16:46

To be honest, there is really no need to make up the length, because the wavelength of 100M is also in the m level, and the difference on the circuit board is not that big. I am just comforting myself.

damiaa

Alas, published on 2022-12-9 17:43 To be honest, there is really no need to make up the length, because the wavelength of 100M is also in the m level, and the difference on the circuit board is not that big. I am just comforting myself.

Haha, indeed. Anyway, just think about it. The isolation transformer of the network port still plays a major role.

Anyway, I have made some products and there have been no problems in this regard.

凌辰_K

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lkh747566933

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lkh747566933

I am currently researching Ethernet gateway design, so I would like to learn from the original poster's design experience.

recheck

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