DP83869HM: PHY Capacitive Coupling (Transformerless Operation) Configuration

Hi User!

It seems like you have answered all of your questions! I'm glad to see that you were able to find all the relevant documents we have available for this topic. Yes, the 33nF are the correct value to use for capacitive coupling and the DP83869HM will support 10/100/1000 speeds. I am unsure why the tolerance of the capacitors is 10%, I agree with your statement, please use a capacitor with a tighter tolerance. As seen on the schematic, if capacitive coupling is desired then the connection goes PHY - Caps - Connector, that's it! Because the DP83869HM is a voltage mode driver, no PUs are required on the MDI lines.

A word of warning, capacitive coupling is not defined in the IEEE802.3 standard and may not pass compliance tests and have worse EMC/EMI performance. 

Regards,

Alvaro

Hi Alvaro,

Thank you for your reply.
I have additional questions regarding your answer.
Please answer the following:

[Question 5]
According to TI application note AN-1519 DP83848 PHYTER Transformerless Ethernet Operation (SNLA088A), it is recommended that for capacitively coupled interface configurations, transformerless operation should be limited to forced 100 Mb/s mode and auto-negotiation should be disabled.
Does the DP83869HM capacitively coupled configuration support operation with auto-negotiation enabled for all 10/100/1000BASE speeds?
Or is it recommended to disable auto-negotiation for all 10/100/1000BASE speeds?

[Question 6]

Alvaro (Al-vuh-roe) Reyes said:

A word of warning, capacitive coupling is not defined in the IEEE802.3 standard and may not pass compliance tests and have worse EMC/EMI performance. 

Regarding the above, I would like to know the following points.
Regarding the DP83869HM, in another thread it was stated that ETHER compliance testing has not been performed with capacitive coupling.
I also found an answer that said, "If you use the DP83869HM, we will support you in debugging if a compliance test failure occurs."
We are also planning to create an evaluation board for capacitive coupling of the DP83869HM and perform an ETHER compliance test.
In the case of a capacitive coupling configuration, would you be able to support us if the ETHER compliance test fails?
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Best Regards,

Hi User,

The DP83869 will support all speeds with auto-negotiation ON. Please note that we do not support 1000Mbps with Auto-negotiation OFF in any configuration.

Of course, we will assist you with compliance.

Regards,

Alvaro

Hi Alvaro,

Thank you for your reply.
Please tell me about the following.

Alvaro (Al-vuh-roe) Reyes said:

The DP83869 will support all speeds with auto-negotiation ON. Please note that we do not support 1000Mbps with Auto-negotiation OFF in any configuration.

Please explain the above.
I understand that it is not supported when auto-negotiation is set to OFF, but is it possible to support a connection between boards with the speed fixed at 1000Mbps in a capacitively coupled configuration?
Also, does this mean that it is not possible to support a connection between boards with the speed fixed at 1000Mbps in a capacitively coupled configuration and a transformer configuration?

Alvaro (Al-vuh-roe) Reyes said:

A word of warning, capacitive coupling is not defined in the IEEE802.3 standard and may not pass compliance tests and have worse EMC/EMI performance. 

Alvaro (Al-vuh-roe) Reyes said:

Of course, we will assist you with compliance.

Regarding the support, I would appreciate your help.
Please tell me about the above.
I heard in another thread that your company has not performed compliance testing with capacitive coupling.
Regarding the above support, is it correct that you can give advice on improving the characteristics of the compliance test, but are not sure whether you can guarantee that the test will pass?

Best Regards,

Hi User

user6236094 said:

I understand that it is not supported when auto-negotiation is set to OFF, but is it possible to support a connection between boards with the speed fixed at 1000Mbps in a capacitively coupled configuration?
Also, does this mean that it is not possible to support a connection between boards with the speed fixed at 1000Mbps in a capacitively coupled configuration and a transformer configuration?

1000 Mbps communication is 100% possible with a capacitive coupled configuration. The point I was trying to make is that auto-negotiation should always be enabled in 1000Mbps. If only 1000Mbps is desired, de-advertising 10/100 speeds in Reg 0x4 is the preferred method, while keeping auto-negotiation enabled. Please see the following FAQ for more information 

user6236094 said:

I heard in another thread that your company has not performed compliance testing with capacitive coupling.
Regarding the above support, is it correct that you can give advice on improving the characteristics of the compliance test, but are not sure whether you can guarantee that the test will pass?

This is correct.

Regards,

Alvaro