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ADV7441A external clock startup

Question asked by vrover on Jun 12, 2012
Latest reply on Jun 13, 2012 by mattp

Hi,

 

I am bringing up a new design.  All my clocks work except for the one going to the ADV7441A, and that signal is just plain dead. 

I am driving the XTAL (pin 66) with a 3.3V 28.636 MHz clock via a 33 ohm series with a Cypress CY22393.  Pin 65 is open

 

If I probe the pin and cycle power, as power goes down,  pin 65 bounces up and then decays.  That makes me think that something in ADV7441A is standing on this pin.  Just for fun, I tried this on a board that had disabled the 1.8V power into the chip (but not 3.3) and on that board, pin 66 has a clock on it but its low level is sitting almost a volt above ground. There is nothing weird about my circuit or the layout.

 

So, here is my question.  You actually have to program the ADV7441A to accept an external clock. I am wondering if it is possible that when it isn't programmed for external clock, pin 66, which is the internal clock output, is going to stand on my clock input that is wired into the chip.  It seems odd to me that if that is so, why not use pin 65 as the external clock input, since it IS an input for the XTAL version too?

 

Thanks!!

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