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DP83848-EP: Is it the same limit also applicable for Hot & Cold temperature ?

Himanshu Panwar
Prodigy 10 points

Part Number: DP83848-EP

Tool/software:

Hello Sir,

 

As per IEEE 802.3 Standard, Differential Output Voltage lies between 0.95V to 1.05.

 

we followed the test standards like :

Texas fixture board : TF-GBE-BTP 1000/100/10 BaseT Basic Test Package (consists of test fixture PCB set and RJ45 interconnect cable).

Oscilloscope with Ethernet license : 5-CMENET Installed option; Ethernet (1000Base-T, 100Base-T, 10Base-T) Automated Compliance Solution for 5 Series Oscilloscope (Min

BW 1 GHz) using TekExpress Automation Platform.

For DP83848-EP IC, is it the same limit also applicable for Hot & Cold temperature @-55DegC & @110DegC resp. for that IC ?

because while testing, we failed at cold condition.

For Cold, Differential Output Voltage is 0.924V.

For Ambient, Differential Output Voltage is 0.964V.

For Hot, Differential Output Voltage is 0.973V.

Thanks 

  • 0
    TI__Mastermind 26125 points

    Hi Panwar,

    Thank you for the detail information. Are you seeing any functional issue for DP83848 at lower temperature?

    --

    Regards,

    Hillman Lin

  • 0 in reply to Hillman Lin
    Prodigy 10 points

    Hi Hillman,

    Diff O/P Voltage Pos is 0.998V at ambient condition while 0.946V at cold condition.
    Diff O/P Voltage Neg is 1.004V at ambient condition while 0.945V at cold condition.

    these voltages is measured before the transformer.

    Supply voltage for DP83848 is 3.337V at ambient, while 3.311V at cold.

    is it the behavior of the DP83848 IC at the lower temperature ?

    Regards

    Himanshu

  • 0 in reply to Himanshu Panwar
    TI__Mastermind 26125 points

    Hi Panwar,

    Supply voltage are the input of the DP83848 which could potentially vary by the external circuitry.

    VOD swing do vary with the different input power supply. Just curious, are you seeing any functional issue with the VOD swing? 

    --

    Regads,

    Hillman Lin

  • 0 in reply to Hillman Lin
    Prodigy 10 points

    Hello Lin,

    The voltage (VOD) difference we are seeing in ambient to cold is 52mV (difference between DIFF voltage at Ambient(+25C) and Diff Voltage at Cold temp(-55C).

    Because of above we are failing Etherent Design Assurance Test at COld temperature ( according to IEEE802.3 standard) - As mentioned above we are using Tektronix fixture board and Tektronix Oscilloscope with Automated SW installed option.

    (also as mentioned above these measurements are before the transformer)

    The VCC supply is 3.337V at Ambient and 3.311 at cold ( the difference is 26mV). 

    My questions are:

    1) Whether PHY(DP83848) differential voltage reduce in the cold temperature?

    2) What could be the other reasons to drop the voltage at cold temperature?

    3) Can you suggest the ways to debug this issue?

    Let me know if you need further information to resolve this issue

    Thanks in advance

  • 0 in reply to Himanshu Panwar
    TI__Mastermind 26125 points

    Hi Panwar,

    There are couple direction I would like to observe:

    • Are you using oscillator or crystal? Did you see a peak to peak drop for either oscillator or crystal? This might be one of the factor result in lower VOD
    • Could you also probe the Rbias pin under normal temperature and low temperature. Did you see a different?
    • If possible, could you share the schematic around the MDI lines? I can quickly go over what might potentially drop the VOD swing on MDI side.

    --

    Regards,

    Hillman Lin