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DP83869HM: First Attempt at Using DP83869HM, No 1.8V, 2 supply

John Smith
Prodigy 10 points
Part Number: DP83869HM
Other Parts Discussed in Thread: DP83869EVM

Tool/software:

Hi,

I created a 100/1G media converter based of the DP83869EVM. So far I have not gotten it to work.

The first issue I observed is that when I power on the media converter with the fiber and copper connected the link LEDs are OFF. And you do not get 1.8V on the VDDA1P8. 

However if I leave the fiber cable disconnected then power on the media converter and finally I plug in the fiber cable. The link LEDs are ON. And you can detect 1.8V on the VDDA1P8. 

My understanding of this, correct me if I am wrong, is that the IC is OFF if I don't get 1.8V on VDDA1P8. Its should know that there is only 2 supplies and go into a 2 supply configuration, and the IC will generate 1.8V. Just like in the EVM where it works automatically. 

I read on this forum that:

"The PHY will be able to detect the presence/absence of the 1.8V rail supply and be able to go into 2-supply mode vs 3-supply. This is why there is a time limit of 50ms max on VDDA1P8 for rail to ramp." 

Please help

  • 0
    TI__Expert 5560 points

    Hi John, 

    First, I wanted to make sure that the power sequencing requirements were being followed. As put in the datasheet, when in 2-supply mode, both supplies must power on at the same time, or if that is not feasible, the following sequence must be used.

    John Smith said:
    My understanding of this, correct me if I am wrong, is that the IC is OFF if I don't get 1.8V on VDDA1P8. Its should know that there is only 2 supplies and go into a 2 supply configuration, and the IC will generate 1.8V.

    Correct, the PHY should be able to generate the 1.8V automatically in 2-supply mode. 

    Have you tried validating the setup in the case where the Fiber is disconnected first, then reconnected after power-up? It looks like the PHY is booting up properly in that case. I also noticed that Copper-to-Fiber mode is not being strapped to according to the schematics. Is this being done through register writes after power-up?

    Best,

    Vivaan