DP83867IR: DP83867 Power Sequencing

Gary Ellerbusch38

Part Number: DP83867IR

Hello

Thank you for taking the time to answer the following question.

I'm looking to use the DP83867 in a Xilinx Zynq Ultrascale+ design. Actually been looking at the Avnet UltraZed design and it uses the DP83867 as its Ethernet PHY. Now looking at the Avnet Design and reading your datasheet and talking to the Avnet ZedBoard forum they recommend this question to you.

In section 10 of the datasheet it shows the 3 supply power configuration and then lists the power supply ramp conditions in regard to the 1.8V and the 2.5V. The 1.8V must be stable within 25ms of the 2.5V but then there is a curious note about this only applies if the 2.5V is used to power other devices up also. Why does this matter? Also it looks like the Avnet design does not follow this and they stated this was not on the original datasheet when they designed it.

So can you please answer if this is a requirement that the 1.8V be brought up with 25mS of the 2.5V. What would happen if the 1.8V comes first before the 2.5V? And why does it matter if the 2.5V supplies the DP83867 only or other devices too?

Thank you for you help

Gary

Reference zedboard.com/.../ultrazed-ethernet-dp83867-power-question

over 7 years ago

0 Ross Pimentel over 7 years ago

TI__Mastermind 23675 points

Hi Gary,

It is required that 1.8V be brought up within 25ms of 2.5V supply. Without this, you will not allow our internal circuity to properly sample the supply voltage and make the appropriate decision on the LDO selection.

Kind regards,
Ross

0 Gary Ellerbusch38 over 7 years ago in reply to Ross Pimentel

Prodigy 80 points

Ross

Thank you for getting back to me.

Ok so if it's not there before 25ms of the 2.5V than the internal circuit will be setup incorrect.

Can it be there before the 2.5V?

And the curious line in the datasheet on page 115.

Note:If the 2.5-V power supply provides power to DP83867 devices only, the 1.8-V supply may ramp up any time before 2.5-V.

So this tells me the 1.8V can come up before the 1.8V then right?

Thanks

Gary

0 Aniruddha Khadye over 7 years ago in reply to Gary Ellerbusch38

TI__Mastermind 18425 points

Hi Gary,

If there is no other device on the same 2.5V rail as the DP83867, then it is ok to bring 1.8V up before the 2.5V.

-Regards,
Aniruddha

0 Daisuke Maeda over 6 years ago in reply to Aniruddha Khadye

Guru 19985 points

Hi Aniruddha-san,

I would like to make clear why it is ok to bring 1.8V up before the 2.5V.

There is the condition below when powering down.

"When powering down the DP83867, the 1.8-V supply should be brought down before the 2.5-V supply."

Does this condition not intend that 1.8V should not be supplied to the VDDA1P8 pins while 2.5V is not supplied to the VDDA2P5 pins?

If there is no other device on the 2.5V VDDA2P5 rail, is this condition not required?

If there is other device on the 2.5V VDDA2P5 rail and this condition is not met, what are the problems?
Is it that the other device is to be damaged by the large current flowing from the 1.8V VDDA1P8 rail to the 2.5V VDDA2P5 rail through DP83867?

Best regards,

Daisuke

0 Daisuke Maeda over 6 years ago in reply to Aniruddha Khadye

Guru 19985 points

Hi Aniruddha-san,

I found the same answer for the power-on sequence.

https://e2e.ti.com/support/interface/ethernet/f/903/p/511963/1864307#1864307

Why is it not allowed that there is other device on the same 2.5V rail as the DP83867?

Best regards,

Daisuke

0 Aniruddha Khadye over 6 years ago in reply to Daisuke Maeda

TI__Mastermind 18425 points

Hello Maeda-san

The power up requirement of the PHY are based on its internal design and observations from validation. This data contains confidential information and we will not be able to share it on open forum. However, the information provided in the datasheet should be enough to design a correct powering scheme for the PHY.

-Regards,
Aniruddha

0 Daisuke Maeda over 6 years ago in reply to Aniruddha Khadye

Guru 19985 points

Hi Aniruddha-san,

Thank you for your reply.

I will contact my local TI representative if our customer requests this detail

Best regards,

Daisuke

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DP83867IR: DP83867 Power Sequencing