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CDCLVP1208: Use the CDCLVP1208 LVPECL to LVDS output

Hugo Liu
Genius 5095 points
Part Number: CDCLVP1208


Hi Sir,

Our customer want to use the CDCLVP1208  LVPECL to LVDS(MAC input type).

But we have 3 question for this application,

http://www.ti.com/lit/ug/scau038/scau038.pdf

Q1: TI document SCAA059C show the Table 2 LVDS input is VCM=2V, Why also show the common-mode voltage to 1.65V?which one is right?

Q2: LVDS is Differential Signalin, Why only Negative have 10k resistors? 

Q3: IF application is LVPECL to LVPECL , We are see the VBB is VCC-1.3V, What is VBB value? MAC VCC is 1.8V,  CDCLVP1208 VCC is 3.3V  

Hugo

  • 0
    TI__Genius 9920 points
    Hi Hugo,
    Here are answers for you questions.
    A1, table 2 shows LVDS input typical Vcm is 1.2V. While real device has a wide Vcm range for LVDS receiver, that's why 1.65V could be used.
    A2, Pin N get the Vcm (2 pcs 10kOhm divider), pin P also would get this Vcm through 100Ohm.
    A3, If MAC VCC is 1.8V, LVPECL output Vcm 2V is over spec., so we should choose AC couple for LVPECL to LVPECL. Not only check Vcm, but also check if Vod (on driver) is in the range of Vid (on receiver).

    regards,
    Shawn
  • 0 in reply to Shawn Han
    Genius 5095 points
    Hi Shawn,

    Thank you very much.

    Hugo