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ADV7842 - Circuit application questions

Question asked by obalaj Employee on Sep 1, 2015
Latest reply on Sep 1, 2015 by GuenterL

Hi there,


Can you please advise regarding the following questions:


1. On the RevC schematics for the ADV7842 front end evaluation board, it says that "series resistors are to be placed as close to the

      ADV7842 as possible and that the traces are to be impedance matched to 75 ohms" for the 36-bit video output bus P[0:35], LLC,
     HS/CS, VS/FIELD, and some additional signals. Are these signals terminated internally to the ADV7842?

     If not, does the impedance have to be 75 ohms or can we use 50 ohms instead? The reason I am asking is because the 75 ohm      impedance will be difficult to achieve on our pcb due to other controlled impedances required.

2. We are using two ADV7842 decoders on our board and due to space constraints they will be operated without external memory. In      the app note for no external memory operation, one of the hardware changes stated is that DQ and DQS lines should be connected      to ground through a 4k7 resistor. Do these lines need to be connected to ground through individual resistors or can they be      connected together and grounded through a single resistor?