DP83826I: Twisted-Pair Interface (TPI) Network Circuit

Xiaoying Lu

Part Number: DP83826I
Other Parts Discussed in Thread: TLK110

Hi,

This is Xiaoying, FAE NCG. And recently I am learning our PHY portfolio.

When I am reading the datasheet of DP83826i, I notice that there is a recommended TPI Network Circuit, in which the transmitter and the receiver of each node are dc-isolated from the network cable by 1:1 transformers. I am curious that whether this transformer is only utilized to provide isolation? If it is the case, why other isolation methods like optocouplers or our digital isolators cannot work?

Also, I notice that there is one app note SLLA327 called TLK110 Ethernet PHY Transformerless Operation. In this note, it describes transfomerless operation using capacitors. Based on my understanding, the capacitors can somehow filter some noise, but cannot provide the galvanic isolation, right? Can you help advise what's the main applications?

Moreover, I know that for high-speed data communication applications, between the transmitter and receiver, there would not be any parts interrupting the serdes line. So I wonder if all the configurations will differ based on the communication speed? Thanks.

Regards,

Xiaoying

over 4 years ago

0 Joe Vanacore over 4 years ago

TI__Genius 17080 points

Hi Xiaoying,

I am looking into your post and I will try to follow-up by the end of business tomorrow.

Kind Regards,

Joe

All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml)

0 Joe Vanacore over 4 years ago in reply to Joe Vanacore

TI__Genius 17080 points

Hi Xiaoying,

The decision to use capacitors over transformers is cost since galvanic isolation is not an IEEE requirement for 100BASE-TX ethernet. If galvanic isolation and better signal integrity are priorities, then we recommend using the transformer TPI circuit. This decision is usually made by the customer when deciding on the tradeoffs for their design.

Kind Regards,

Joe

0 Xiaoying Lu over 4 years ago in reply to Joe Vanacore

TI__Expert 4270 points

Hi Joe,

Thanks for your reply! Just a follow up question, based on my understanding, customers do not use optocouplers or our digital isolators to do the isolation because the limited data rate of these devices, is that correct?

Xiaoying

0 Joe Vanacore over 4 years ago in reply to Xiaoying Lu

TI__Genius 17080 points

Hi Xiaoying,

I will look into your question and I hope to get back to you by the end of business Monday (6/7).

Kind Regards,

All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and is subject to TI’s Important Notice (www.ti.com/.../important-notice.shtml)

0 Joe Vanacore over 4 years ago in reply to Joe Vanacore

TI__Genius 17080 points

Hi Xiaoying,

The two most common methods for signal isolation are magnetics or capacitors. For optical isolation, we have the DP83822 that complies with the 100BASE-FX standard.

I believe the decision for the specific isolator comes down to the type of isolation required in the design. I hope that helps and please let me know if you need any additional information.

Kind Regards,

Joe

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DP83826I: Twisted-Pair Interface (TPI) Network Circuit