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ADV7511W-PLL is not getting Locked

Hi,

I am using 3 ADV7511W ICs on my board. I am using 16 bit data lines for YCbCr data transmission. Out of three ICs on the board, for one ADV7511 IC I am not getting the output. When we read the registers we got to know that register 0x9E is 0 i.e PLL is not getting locked. I checked the REXT resistor value. The resistance is 886ohm.I have also probed and checked for the noise in PVDD PLL power supply. The ripple looks within the acceptable limits. The hardware design used for all three ICs are same. Same issue is observed in all the boards. Each board has one ADV7511 IC were PLL is not locked and remaining two ICs are working fine.

Can you please let me know what may be the reasons why PLL is not getting locked.

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  • Hi,

      Please ensure with below things for PLL unlock issue,

     1. Make sure with R_EXT resistor whether you have been using '887' Ohms resistor( Part is only spec'd for the 887 Ohm resistor) this might be the chance for PLL unlock issue.

      2. Ensure that the pad underneath is making good connection to GND.

      3. Ensure the grounding of the ADV7511 whether Gnd-Pads are soldered properly.

      4. Is your PVDD isolated from the other supplies as shown in Figure 21 of the ADV7511W programming guide or is it tied to them?

      5. Ensure your PCB layout is correct at HDMI Layout Guideline However, if you are working on a new board, you will need to verify that the ADV7513 is connected correctly to the HDMI connector and that the PCB layout is correct.

      6. Also ADV7511 PLL locks depend on the incoming video CLK line.  So the CLK line must be stable, no jitter.  Make sure there is low noise on the power rails.  Rset adjusts the output square wave amplitude.  Lower values gives greater amplitude.  Nominally the TMDS lines should be +-300mV with and offset of 3Vdc

    Note:   R_EXT
    External reference resistor should be connected between the R_EXT pin and ground with as short a trace as possible. The external reference resistor must have a value of 887 Ohms (+/-1% tolerance). It is strongly recommended to avoid running any high-speed AC or noisy signals next to the R_EXT line or close to it. Specifically it is recommended that no switching signals – such as LRCLK (including vias) be routed close to R_EXT pin (14). Low-level TMDS switching noise should have minimal impact on R_EXT. Therefore, it is acceptable to place a via for R_EXT near TMDS signals such as TX0+ and TX0- .

    Thanks,

    Poornima

  • Hi Poornima,

    1. I have used correct value of resistor.

    2. The grounding for ADV7511 is proper.

    3. PVDD is isolated from other power supplied as recommended and the layout guidelines are taken care.

    The observation from working and non working board:

    When probed the voltage at R_EXT pin, in working condition we have 0.5V  and non-working condition we have 1V at R_EXT pin.

    May I know what is this difference in voltage convey. Also does R_EXT has any internal pull up resistor?

  • R_EXT is used to set and internal current reference.

    1) Are you comparing two of the same boards, one working and the other not working?

    2) Check the power rails to make sure they are the right voltage also.

    3) With DVM measure R_EXT value to make sure they are the same.

  • Hi Guenter,

    I have 3 ADV7511 ICs on the same board. Hence I measure the voltage on the same board working and non working IC.

    2. Probed all the voltages and they are as expected.

    3. I checked R_EXT value and it is 886ohm.

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