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ADC3644EVM: Schematic sheet clarification and unused channel

Part Number: ADC3644EVM
Other Parts Discussed in Thread: ADC3644, ADC3564


I am looking at the ADC364xEVM_RevF(004)_Sch_2022-04-01.pdf schematic sheet for the ADC3644 and am confused by the use of 'X' through components. For example, does an X through a resistor mean to remove that resistor or replace it with a short? Same for inductors and capacitors. 

Additionally, I only want to use 1 of the two ADC channels. I believe I can leave the digital outputs (DB0-DB6) floating since they are CMOS outputs, but I was wondering what to do with the B channel analog inputs (BIN_P and BIN_N)? Can they just be tied to ground or VCM?


  • Hi Troy,

    The X through any components means that the component is not populated, allowing us to provide multiple operational modes via HW modifications. If you are only wanting a single channel, then you can power down the channel using the GUI. If you are asking about how to incorporate into a design, then I would suggest using the part ADC3564 which is a single channel, equivalent device. 

    Regards, Chase

  • I should have clarified that I am trying to incorporate the ADC3644 into a design. We wanted to go with the ADC3564 but its not currently in stock, so we want to use the 3644 and then just not use one of the channels. What's the best way to lay the second channel out so that it won't mess up the operation of channel 1? Also, if we use the ADC3644 in the single ended input mode and provide a AC coupled signal as our input, do we still need to implement the glitch filter and termination network?



  • Okay, I see now. Thanks for the added details.

    We definitely would recommend using a glitch filter if driving this part single ended or differentially. Is there any particular reason you are driving this single ended? Just a space constraint for a balun? As I'm sure you've noticed, the dynamic range will be cut in half causing an instant loss of 3dB since the analog input can only swing half the voltage. Additionally, HD2 performance will be worse since there is no inherent noise-cancellation from differential signaling. In either case, you can terminate channel B analog input to VCM and leave the channel B digital outputs floating. Since channel B won't be used at all, you shouldn't need any capacitors to hold the VCM stable, however more capacitance will only help VCM remain constant, so that is up to you.

    Regards, Chase 

  • Yes, at first glance I thought we wouldn't have space to fit a balun, but after taking a closer look, we should be able to make it work. I think we'll definitely go down that route then. That helps a lot! Thanks for your help.