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CDCLVP1216: CDCDLVP1216 DC coupling

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Replies: 7

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Part Number: CDCLVP1216

Hello,

Let me confirm about below.

* When user use this device in case of DC coupling, how should user terminate output side ?

According to datasheet of CDCLVP1216, there is figure(figure 12) about DC coupling. In this case, it seem that output termination is NOT required.

In my case, output is LVPECL(CDCLVP1216) and input is LVDS(DS90LV110T). On the other hands, according to datasheet of DS90LV110T, it seems that output termination is required(Please see figure 12 of DS90LV110T datasheet).

So, could you please confirm how user should terminate output side of CDCLVP1216 in this case ?

Best Regards, 

  • You might consider CDCLVD1216. CDCLVD1216 has the same package, pinout, and function as CDCLVP1216, except it hasLVDS outputs rather than LVPECL.

    If you still prefer to use CDCLVP1216, you could use the circuit in Figure 12 or Figure 13 of DS90LV110T datasheet to connect an LVPECL input.

    Figure 12 of DS90LV110T datasheet shows a 100-ohm resistor integrated in the DS90LV110T input receiver, however the device does not appear to have an integrated differential termination. I think it should be external. If you require additional support with DS90LV110T, please submit a new post and the responsible experts can address your questions.

    Kind regards,
    Lane

    ____________________________________________________________________________________

    To design your own Clock Tree solution, visit WEBENCH Clock Architect ​​​​

    More information Clock and Timing System products: http://www.ti.com/clock-and-timing/overview.html

  • In reply to Lane Boyd:

    Hello Lane-san,

    Thank you for your reply.

    Which value should user implement as pull down resistor ?(150 ohm or others ?)

    Your assumption is correct. I asked about CDCLVP1216.

    Best regards,

  • In reply to Ryuuichi machida:

    For CDCLVP1216 with DC coupling, use the circuit in Figure 12a or Figure 13a. 

    Kind regards,
    Lane

    ____________________________________________________________________________________

    To design your own Clock Tree solution, visit WEBENCH Clock Architect ​​​​

    More information Clock and Timing System products: http://www.ti.com/clock-and-timing/overview.html

  • In reply to Lane Boyd:

    Hello Lane-san,

    DS90LV110T have large Common mode input range. So user need to attenuate. However, according to datasheet, it seems that this device does not have internal termination resistor.

    When we connect DS90LV110T, input of DS90LV110T just terminate by using 100 ohm. So, there is no current path to GND at LVDS input side. 

    Therefore, I believe that user need to add current path to GND at LVPECL side. What I ask is which value user should add resistor between signal path and GND.

    Best Regards,  

  • In reply to Ryuuichi machida:

    Thanks for explaining it again. My last response was incorrect, the circuit in Figure 12a / 13a will not work because DS90LV110T is an LVDS input, not an LVPECL input. Sorry for the confusion.

    When converting from LVPECL to LVDS, here is the typical circuit:

    • place the 150-ohm resistors to GND at the CDCLVP1216 outputs for biasing.
    • After the 150-ohms, place a 70-ohm resistor in series with the trace to attenuate the swing.
    • At the DS90LV110T input, place AC coupling capacitors before the 100-ohm external termination so that you can shift the common mode bias at the receiver.
    • Use a resistor divider to generate the common bias at the receiver. For DS90LV110T, use Rtop = Rbottom = 5K-ohm

    I hope this helps

    Kind regards,
    Lane

    ____________________________________________________________________________________

    To design your own Clock Tree solution, visit WEBENCH Clock Architect ​​​​

    More information Clock and Timing System products: http://www.ti.com/clock-and-timing/overview.html

  • In reply to Lane Boyd:

    Hello Lane-san,

    Thank you for your reply.

    >place the 150-ohm resistors to GND at the CDCLVP1216 outputs for biasing.

    >After the 150-ohms, place a 70-ohm resistor in series with the trace to attenuate the swing.

    Are above items for both pins of differential(User need to add 150 ohm to both P and N) ?

    Best Regards,

  • In reply to Ryuuichi machida:

    That is correct, please do this for both the P and N pins.

    Kind regards,
    Lane 

    ____________________________________________________________________________________

    To design your own Clock Tree solution, visit WEBENCH Clock Architect ​​​​

    More information Clock and Timing System products: http://www.ti.com/clock-and-timing/overview.html

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