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ADV7182 Slow To Sync

Category: Hardware
Product Number: ADV7182

Hi, 

A circuit I designed uses the ADV7182 application circuit as set out in the datasheet.

I've noticed that on first power-up, the chip is very slow to achieve lock with any known good video signals - up to several minutes.

I've checked the clock frequency and tried driving it with multiple sources, but the problem persists.

Once the circuit has been running for a few minutes it locks to any video signal immediately, no problem: there's only an issue in the first few minutes after powering-up.

Enabling "fast lock" as described in the application note has no effect.

Any ideas on what would be causing this are greatly appreciated.

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  • Hi,

       Please ensure whether you are following the order given in the fast switch script.

       Also note that some functionality (like Macrovision) doesn't work in fast switch mode.

       Kindly ensure with below expert suggestion,

         For some reason the input signal on your board is floating or leaking to a supply instead of ground which often happens.

         After the AC coupling capacitor, the signal can float, the internal clamps turn on and pull the signal to the correct level. If there was large leakage on the board to a supply voltage, it could be outside the clamping range ( Too high) and the clamps may take time to turn on and clamp the signal.

         As an experiment to prove this if you add a large resistor few MOhm to ground from the Ain pin, this will pull it to ground. That is only an experiment to prove the point.

         For register settings, if you add the following writes to your script, it may help.

    Please add just after switching or connecting new input.

    42 0E 80

    42 9c 00

    42 9c FF

    42 0E 00

      This forces the clamps to respond very quickly.

    Also the power-up sequence described in the datasheet is the most conservative / correct way of powering up the ADV7182. Care must be taken to ensure that a 1.8V supply does not go higher than the 3.3V supply during power-up.

    Also the 5ms reset after power-up is required.

    Thanks,

    Poornima

  • Yes that seems to have solved the problem, thanks!

    Is there also any way to adjust the frequency in free-running mode. It tends to run a bit too fast, even though the input crystal frequency is correct, which means the colour subcarrier is off.

    Thanks

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