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AD9550 PLL Lock Failure

Question asked by Banj on Jun 27, 2017

Hello,

 

I am evaluating the AD9550/PCBZ board and I am having problems locking the PLL of the board. I don't have a clue as to what might be wrong with the board. I am generating a 155.52MHz LVPECL output using a 122.88MHz RefA input. The indicator for PLL lock does not detect signal, but voltage is present on the schmitt trigger used for the lock detect signal. One thing I observed when I debugged the board is that no lock signal is present coming from the DUT pin. Is it something related to the loop filter? The loop filter components are listed below:

R48 = 6.8kOhms

C15 = 47nF

C3 = 1uF

 

Thanks for all the help.

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