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DS90CF383B: Level Shifts

Abigail Leonardi
Intellectual 2655 points
Part Number: DS90CF383B

Tool/software:

Hi,

One of my customers is experiencing issues interfacing the LVDS serializer with a Winstar display using NV3051F-L LCD driver.

When the DS90CF383B drives simple 100 ohms terminations, the LVDS signals are OK, but when driving the NV3051F-L LCD driver the LVDS DC level shifts based on the data being sent.  They are using a continuously driven 50MHz clock as the PCLK.  This DC level shift prevents the display from operating normally.  Can you please help us figure out how to fix this?

  • 0
    TI__Expert 5550 points

    Hi Abigail,

    From our device to the sink, we expect the LVDS channels to be terminated at 100 Ohms. In terms of the DC level shift, this would not be due to our device. Rather, it would be related to the design (schematic/layout) on the LCD driver side. 

    BR,

    Esther

  • 0 in reply to Esther Chang
    TI__Intellectual 2655 points

    Hi Esther,

    Thanks for your answer, to clarify if we had a schematic to review for the DS90CF383B would it help at all in the debug process? Or not, because its largely dependent on the NV3051F-L LCD driver?

    Has the team dealt with this particular LCD driver before or had any reference designs?

    They let me know as well during the set up process NV3015F-L’s datasheet specifies the value for internal termination resistors as between 80 to 140 ohms.  However, they were able to get things working by adding discrete termination resistors near the connector for the display. Which seemed odd as the resistors would then be in parallel with the internal resistors.

  • +1 in reply to Abigail Leonardi
    TI__Expert 5550 points

    Hi Abigail,

    Just to make sure I'm interpreting this correctly, can you send me a block diagram of the system?

    Based on the information provided, this issue is largely dependent on the LCD driver. It's likely the 80 - 140 Ohm resistors in the LCD driver is causing the DC level shift. Our device requires that there be a 100 Ohm+/-10% termination resistor between our LVDS lines, but their internal termination resistors have such a large range.

    We haven't dealt with this specific LCD driver before, and I would suggest discussing with the LCD driver vendor and see if they are able to set their internal termination resistor to 100 Ohms, and then they can remove the discrete termination resistors. 

    Overall, our device needs ~100 Ohm+/-10% Ohm termination resistors on the LVDS lines and if the vendor is capable of maintaining that resistor value, the DC level shift shouldn't occur. 

  • 0 in reply to Esther Chang
    TI__Intellectual 2655 points

    Hi Esther, they just sent me over the schematic snippets - I will loop you in over email and close this thread.

  • 0 in reply to Abigail Leonardi
    TI__Guru* 99190 points

    Hello,

    the team is out due to the Holidays. Responses will be delayed from Dec. 24 through Jan. 2.

    Thank you for your patience