DP83867IR - center tap of RJ45 with pulse trans

Hirotaka Matsumoto

Other Parts Discussed in Thread: DP83867IR

Hi all

Would you mind if we ask DP83867IR?

Our customer would like to use the attachment file's RJ45 with pulse trans.
20160923_RJ45 connector with PulseTrans.pdf

<Question>
We have heard followings on Ether-forum;
-Center tap is pulled to VDD since the driver we use is a current mode driver.
-If it were a voltage mode driver we would have center tap to GND.
-Since the transformer isolated the ground planes between the link partners, we can use either type.

Is DP83867IR the current mode driver or the voltage mode?
How much of Pull-up voltage is suitable? VDDIO level?

Kind regards,

Hirotaka Matsumoto

over 8 years ago

0 Ross Pimentel over 8 years ago

TI__Mastermind 23675 points

Hi Hirotaka,

The 867 is a voltage mode line driver.
You do not need terminations and do not need to pull the line up.

Kind regards,
Ross

0 Hirotaka Matsumoto over 8 years ago in reply to Ross Pimentel

Guru 27585 points

Ross san

Thank you for your reply always.
If our customer use 93637-8617 with DP83867IR, there is no connection to pull-up, right?

And then, 93637-8617's inserson loss is 1.3dB@100MHz.
It seems that it is not enough value(It require 1.1dB@100MHz.)
So, we have to encourage to ourcustomer to use HX5008FNL and H5007NLT.
Is our recognition correct?

Kind regards,

Hirotaka Matsumoto

0 Ross Pimentel over 8 years ago in reply to Hirotaka Matsumoto

TI__Mastermind 23675 points

Hi Hirotaka-san,

No pull up. Also, if you need a connection reference, please have a look at the 867evm. In the schematic and user's guide you will see proper connection needed.

Kind regards,
Ross

0 Hirotaka Matsumoto over 8 years ago in reply to Ross Pimentel

Guru 27585 points

Ross san

Thank you for your reply.
We would like to confirm two points.

<Point 1>
If our recognition about insersion loss is incorrect, could you let us know?

<Point 2>
Center tap(phy-side) capacitances of MOLEX 93637-8617 are connected to center taps together.
Is there no problem?

Kind regards,

Hirotaka Matsumoto

0 Rob Rodrigues over 8 years ago in reply to Hirotaka Matsumoto

TI__Mastermind 19780 points

Hi Hirotaka-san,

Yes, your point about insertion loss is correct.

It is recommended that the center taps are separate nets for the DP83867. Connecting the center taps together is not recommended, connecting the CTs together is done inside of the Molex connector you have linked.

Best Regards,

0 Hirotaka Matsumoto over 8 years ago in reply to Rob Rodrigues

Guru 27585 points

Rob san

Thank you for your reply always!

If it is possible, could you let us know the reason why it is recommended that the center taps are separate nets for the DP83867?
(Of course, we pesuade our customer to use HX5008L or H5007NLT.)

We appreciate your help always.

Kind regards,

Hirotaka Matsumoto

0 Rob Rodrigues over 8 years ago in reply to Hirotaka Matsumoto

TI__Mastermind 19780 points

Hi Hirotaka,

There could be problems with noise from other channels if all the CTs are joined together like this.

Best Regards,

Interface

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DP83867IR - center tap of RJ45 with pulse trans