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DS90UB947-Q1: There is 31MHz signal during EMC testing

Lian Wu
Genius 5250 points
Part Number: DS90UB947-Q1

Dears:

There is infotainment system to have a EMC testing and they found there are a 31MHz signal between DS90UB947-Q1 and DS90UB948-Q1.

I have checked schematic and Layout requirements with customer, I didn't find any issues.

The EMC test standard is Ford standard and didn't have the plot for the EMC test.

There is only 124MHz clock from DS90UB947 providing to Sun's 827.

Pls. kindly help to give some advice, thanks

Luck Wu

  • 0
    TI__Genius 10475 points
    Hello,
    We received your question and this has been assigned to an Apps engineer to review and respond to.
  • 0 in reply to Palaniappan Manickam
    TI__Mastermind 30515 points

    Lian,

    to better understand your issue, could you please elaborate "there are a 31MHz signal between DS90UB947-Q1 and DS90UB948-Q1", and "There is only 124MHz clock from DS90UB947 providing to Sun's 827."?

    From the your test system and UB947 & UB948 device's function, the 124MHz should be LVDS clock and UB947 is sink. But what is the 124MHz clock EMC source? also, to generate this 124MHz LVDS clock output, does it have any XO or other clock source? please dig out this clock trace to better understand the 31MHz EMC issue (124 = 31 x 4).

    also, please share the EMC test plot to better understand the test result and further dig out the 31M source in  your system.

    rgds,

    Steven

  • 0 in reply to Steven(Shenzhen) Shi
    Genius 5250 points
    Hi Steven:
    Sorry for my mistake, UB948 is integrated in LVDS Display, and the 124MHz is provided to LVDS Display(Sun's 827). We have checked other clock sources, there are no any multiple relationship clock sources.
    You know UB947 and UB948 are used together in solution and the hardware' lines are connected, is there any method to test UB947's or UB948's EMC individually?
    Or can you give some test method to dig out clock trace?
    Many thanks!
    Best regards
    Luck Wu
  • 0 in reply to Steven(Shenzhen) Shi
    Genius 5250 points
    Hi Steven:
    Pls. kindly help me, thanks!

    rgds,
    Luck Wu
  • 0 in reply to Lian Wu
    TI__Mastermind 30515 points
    Luck,
    could you check the connector / cable? you can shield these with good grounding. Please make sure the high speed signal PCB layout with good SI performance, and good shielding performance.
    also, please check the UB947's board, what is the processor and pixel clock? I guess this processor should have one clock source to generate LVDS's 124MHz. please isolate the issue module by module.

    thanks.

    best regards,
    Steven