DP83849IF: Media converter : DP83849if(LVPECL) to Optical_transceiver(CML)

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Replies: 3

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Part Number: DP83849IF


I am using an optical transceiver that has an AC-coupled CML differential input and output.

I made the LVPECL termination for the DP83849IF as follows --> (TX+- pins: 50 Ohm to 3.3V, RX+- pins : 82 Ohm to 3.3V and 130 Ohm to GND, 0.1 µF coupling capacitors in series with all 4 lines).

With this termination the communication did not work.

I tried below setup as described in section 3.4.1(https://www.ti.com/lit/an/snla086b/snla086b.pdf) without firmware (no read & no write) to monitor the data on RXD lines for both PORTA and PORTB.

I have noticed that the PORTA - RXD0_A to RXD3_A lines are always 0. These lines show no  pulses when I connect the RJ45 to PC. This means that the PORTB transmit pins are not transmitting.

I think this is because of the termination and biasing of the LVPECL outputs.

Could you please tell me what should I connect to 100base-FX differential signals of DP83849if  to make the conversion from LVPECL to CML ?

Thank you.

3 Replies

  • Hi 

    Are you able to check link up status; is there a successful link? Please review the following and check your fiber optical transceiver: https://www.ti.com/lit/df/snlr002/snlr002.pdf Are you using a different transceiver?

    Thank you,


  • In reply to Nikhil Menon:


    I am using different transceiver which has ac coupled differential CML inputs and output.

    Linkup status is 1 . Please find the attached images for PORTA and PORTB registers values.

    Thank you.



  • In reply to Yash Naik:

    Hi Yash,

    This seems to be a duplicate of another thread you have posted. For better continuity I will close this thread, and our team will respond to the thread linked here: 

    Thank you,