DP83867E: Question about TI_DP83867ISRGZ Ethernet PHY magnetic connections

Kai Lai

Part Number: DP83867E
Other Parts Discussed in Thread: DP83TG720EVM-MC, DP83TC812EVM-MC

Tool/software:

Dear TI experts,

Referring to the datasheet link below at page-105, Figure 8-2 show that the center tap of transformer had independent connection closed to PHY side. But we found some other solutions wired all center taps together. Our questions are as followers

Any difference of these two structures?
Which one is better and TI proposed?

DP83867E/IS/CS Robust, High Immunity, Small Form Factor 10/100/1000 Ethernet Physical Layer Transceiver datasheet (Rev. F)

Thanks and look forward to hearing from you soon.

Best,

Kai

6 months ago

0 David (ASIC) Liu 6 months ago

TI__Guru**** 177796 points

Kai

Please see this FAQ for how to choose the magnetic, https://e2e.ti.com/support/interface-group/interface/f/interface-forum/1161575/faq-dp83867e-how-do-i-choose-magnetics-for-my-industrial-phy.

The center tap of the transformer provides a common mode voltage. In the case of 10M/100M, the third and fourth pair of Ethernet PHY link are not used. If shorted together, this could cause the the common-mode voltage between the operational and non-operational pairs to be different and create possible link up issue.

So we recommend people to have the center tap of the transformer to be independently connected.

Thanks

David

0 Jones Hung 6 months ago in reply to David (ASIC) Liu

Prodigy 60 points

Hi David,

Thanks for your reply.

The other question is if we choose 10M/100M Ethernet PHY (like DP83822IRHBR), then what do you recommend how to allocate these two center taps?

1. RCT and TCT Independent connection or short them together?

2. Any pros and cons of these two individual configurations?

Regards,

Jones

0 David (ASIC) Liu 6 months ago in reply to Jones Hung

TI__Guru**** 177796 points

Jones

For DP83822, please see below for the MDI implementation.

Thanks

David

0 Jones Hung 5 months ago in reply to David (ASIC) Liu

Prodigy 60 points

Hi David,

Yes, I see this diagram in DP83822 datasheet and it connected both of TCT and RCT together.

However, most of RJ45 connector which built-in transformer and short 4 center taps as default configuration. As you said, it might suffer connection issue once 10M/100M transection were linked.

Does it mean only discrete RJ45 jack and standalone transformer can be satisfied with 10M/100M/1G link speed Ethernet controller or PHY? How do you think?

Regards,

Jones

0 David (ASIC) Liu 5 months ago in reply to Jones Hung

TI__Guru**** 177796 points

Jones

There are 1G Mag-Jacks in the market in many different flavors; not just center tap short. For example, our DP83TC812EVM-MC (which has DP83867) has a 1G mag-jack which is compatible; AR11-4647. DP83TG720EVM-MC (also has DP83867) has 7499111614A. So even with integrated RJ45, I would recommend to choose one that do not have the center tap shorted together.

Thanks

David

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DP83867E: Question about TI_DP83867ISRGZ Ethernet PHY magnetic connections