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LMK03328: Termination requirment for OUTxP/N _LVPECL

Abhishek Kumar Singh
Prodigy 20 points
Part Number: LMK03328

Hi  Team 
We are using  LMK03328 LVPECL output in one of  our appliaction for  generating various  various  reference  clock for  differrent PHY  . Below are the  spec of REFCLK 

1)   Vppd=600-1200 mV  
        Rdiff=80-120 ohm  , Internally  biased  , internal 100 ohm termination 

2)Differentail  voltage swing  Vpp= 500-1600 mV 
    Differential Input Impedence =160-240 ohms 

3)Differentail  voltage swing  Vpp= 300-1200 mV 
Differential Input Impedence = High  impedence 

how  I should  terminate  outputs  and  select  various  resistance  values  to  control the  swings  with the  receiver  spec ?  

  • 0
    TI__Expert 4845 points

    Hello,

    In order to properly recommend output termination, I have a few questions:

    - What is the center voltage you are looking for?

    - What device are you driving in this system?

    - Is your specified Vppd/Vpp more reflective of VOD or VOUT-DIFF? [see image below for visual depiction of each]

    Best,

    Cris

  • 0 in reply to Cris Kobierowski
    Prodigy 20 points

    Hi  Cris

    What is the center voltage you are looking for?

    Abhishek :  By center  voltage  do you  mean common mode  voltage ? if  yes  then No  requirment is  given by  Broadcomm . Receiver  is  internally biased  

    it has  to  be AC  coupled  on  board. 

    - What device are you driving in this system?

    Abhishek : BCM54192, BCM54998SM, BCM 82399

    - Is your specified Vppd/Vpp more reflective of VOD or VOUT-DIFF? [see image below for visual depiction of each]

    Abhishek :  Vpp/Vppd  is  Vout Diff. 

  • 0 in reply to Abhishek Kumar Singh
    TI__Expert 4845 points

    Hello,

    - Could you provide the datasheets for the devices being driven? It will give us the information to provide a more detailed answer.

    - For your first spec, you can use a CML output and use the following schematic to attenuate to your given specs.

    RP and RN are used for adjusting the common-mode voltage and CD is used to filter out common-mode noise, but RT is used for the actual amplitude attenuation. In your case, you would want to use RT = 150 ohm to meet your spec. 

    RT = 50×VSwingReceiver / (VSwingDriver - VSwingReceiver) with VSwingDriver = 600mVOD as specified in the datasheet.

    - For specs 2 and 3, an LVDS output can be used to meet your spec.

    Best,

    Cris