DP83826E: transformer side TD and RD, offset is oscillating between 1.8V and 1.0V

Hai xuan

Part Number: DP83826E

Hello all,

The DP83826E on our PCB is not working with 100Mhz, basically, be able to be linked with a router but never could get the ethernet work with 100M. Ping or Lwip all failed with 100M, but 10M works.

1) I found the TP_p/n and RD_p/n have a step or oscillating behavior. is this the design of 10M preform?

And, when linked. offset of TP is ~1.8V, but that of RD is 1.0V on our PCB.

2) I found the Voltage of Cext is 1.64V on EVM board, but 0.8V on our own PCB. will it be saying something. should I change the Cext to higher to try (Now is using 2nf as datasheet).

Anyone please help to check.

over 1 year ago

0 Gokul Koraganji over 1 year ago

TI__Mastermind 19150 points

Hi Xuan,

Is this issue related to this one from you? https://e2e.ti.com/support/interface-group/interface/f/interface-forum/1111017/dp83826i-100m-mode-never-get-rx_d-x-signal-and-rx_er-always-comes-just-like-rx_dv

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Regards,
Gokul.

0 Hai xuan over 1 year ago

Prodigy 20 points

Yes, we spent many time on this, still did not found root cause.

Could you have a look my problem and give us some suggestion? I checked DP83826EVM board, the TD and RD offset both are ~ 1.7V, but our PCB is showing 1.8V TD and 1.0V RD after the link is built on 100M.

What will be cause? all schematic just same as EVM, expect I use a transformer integrated RJ45, but with totally same parameter as the separated one in EVM as well.

I saw datasheet about power up sequence, Pedestal Voltage need less than 0.3V. Only thing I could suspect now is this.