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PCM1865: PCM1865 to OPA1637DGK connection

Ignacio Olazabal
Prodigy 40 points
Part Number: PCM1865

Im connecting OPA1637DGK differential outputs to a PCM1865, Im having toruble understanding the common-mode voltage connection. Do I need it? When do I need it? I thought i did so i connected them as shown in the pitcture, but im not sure i need this connection. Just to clarify they are in separate boards connected through a connector, these are the pictures of the schematic. I might not need to connect VCOM because i dont see any common voltage requirements on the PCM, but i still cant wrap my head around it

  • +1
    TI__Expert 5715 points

    Hello Ignacio,

    I am assuming there are 4 op-amps providing differential signals to the PCM1865, correct? Taking IN1P&M inputs as examples, you want to connect a VCOM from the op-amp to the ADC, correct? It is not very clear where the "VCOM 1 4 B" terminates on the IC. And please explain why are you trying to connect that terminal to the IC? 

    I also noted a couple things on your schematic. Please follow these guidelines:

    • connect 1uF to vref as stated in the datasheet

    • your differential input cannot exceed the full-scale limit at 4.2Vrms.

    • The circuitry around the input looks fine, but make sure you include dc blocking caps as they are required at the input. They can be implemented like this: 

                     

    regards, 

    Ore.

  • 0 in reply to Ore Ogundana
    Prodigy 40 points

    I conducted further research and could understand the topic better and was able to answer my question, none the less your remarks were very helpfull, thanks!