a question about transformer used in ethernet application.

[ilikebbs]

As you all know that transformer is used between PHY and RJ45.
My question is that why CT pin always connect to power。

Is it necessary?
Anybody can give your suggestion.

thanks

 

[VVV]

Re: a question about transformer used in ethernet applicatio

The drivers are usually open-drain, that is why the center tap is connected to power, so the drivers can drive the transformer.

 

[ilikebbs]

Do you mean that MDI pin of PHY are open-drain?
So why center tap is connected to the power?
We can also pull up MDI pin.
thank you for further explaination.

 

[budhy]

Re: a question about transformer used in ethernet applicatio

We can also pull up MDI pin.

You right. the transformer is the pull-up compnent, so the signal is transformed to the net.