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DS92LX1621 and DS92LX1622 lock lost

Other Parts Discussed in Thread: DS92LX1622

Hi

We use DS92LX162x since a few years in our video-products (over 6000 units). We have increasing problems with the stability of the Channel-Link III path (loosing lock --> flickering).
Each unit has two identical signal pathes  (with one DES each channel at the same PCB) In case of fault one channel has the flicker problem the other works right.
Both ICs have separated but identically built power decoupling.  All signal-pathes are "copied". But one channel causes problems. And after cross exchanging the IC the problem moves with the IC. --> Are there some known tolerance effects ? 
Settings are all the same. Also changing the LC filtering etc. doesn't help. The Equalizer settings has a minimal effect, but the problem itself persists.
The register settings are not well documented. Are ther some undocumented register setting whith could help ?

Could you give me please a hint, what else we can do .
Thank you

  • Hi Popp,

    1). If you are seeing video flickering, i am assuming DS92LX1622 is going in and out of lock possibly. Could you please probe pin 28, Lock pin of the DS92LX1622, to see if this is the case?

    2). As noted in the data sheet, the DS92LX1622 register 0x27 need to be initialized to a value of 0xE0. Please confirm you are initializing register 0xx27 with 0xE0 value. Here is a link to the DS92LX1622 data sheet:
    www.ti.com/.../ds92lx1622.pdf

    Also, please note transmission media section of the data sheet to make sure the media complies with the requirements noted in this section.

    Regards,,nasser
  • Hi Nasser

    Thank you for reply.

    Yes, everything is OK, register 0x27 is written with 0xe0 and lock pin is dropping. We changed also the cabels but nothing helps.

    And the most magic thing is, that the identically built circuit (at the same PCB) works well.

    We also have seen, that cooling this chip leads in to more droppings. Do you know other registers we can work with ?

    Thank you

    Regards Toralf

  • Hi Toralf,

    Given lock pin is dropping or toggling, this means signal quality or signal to noise ratio is not good enough to maintain a reliable lock condition. There are several sources that could contribute to the poor signal quality. If i understand it right, one channel is working fine and the 2nd channel is not reliable. You also mentioned if you swap the devices the problem moves with the device. Given this, i am thinking there could be some parameter that is on the margin. For example, transmit PCLK jitter. Could you please check your transmit PCLK to make sure this clock is stable and has very low jitter. We should try to maintain PCLK jitter to below 1/10th of the data rate unit interval. For example if we are running at 1Gbps, it means transmit PCLK jitter should be below 100pS. You can monitor this signal and put your scope on infinite persistence mode to capture potential clock jitter. Another potential cause for poor signal quality could be due to the power supply noise. What type of power supply are you using? Can you use a linear power supply or improve your power supply DC coupling to reduce low and high frequency noise to see if this would make a difference? Lastly, if it is possible please send us a block diagram of your system so we can get a better understanding of the overall system block diagram.

    Regards,,nasser