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LVCMOS25 digital inputs OK for DAC5672A??

chip
Prodigy 55 points
Other Parts Discussed in Thread: DAC5672A, DAC5672

I have an FPGA board with an FMC connector and I want to make a plugin FMC board with the DAC5672A 275 MSPS 14 bit dual channel DAC. 


The FPGA banks that connect to the FMC connector use 2.5 V rails, so IO will be LVCMOS25 (or LVDS_25, but I was not planning to use that).  I measured the FPGA LVCMOS25 digital high outputs and they are 2.5 V. 

The DAC5672A data sheet Digital Inputs section calls for high level inputs in the 2 - 3.3 V range. 

So, is it OK to use LVCMOS25 outputs from an FPGA  as digital inputs to the DAC5672A?  Do I need something in between to buffer or translate voltages?  The data sheet says that AVDD and DVDD can be from 3 - 3.6 V.  Would it help to reduce DVDD from 3.3 down to 3V?

Thanks.

  • 0
    TI__Mastermind 20541 points
    Hi,

    I think you should be fine with using LVCOM25. I will consult with design team on Monday and let you know if they think there will be any problems with that.

    Regards,
    Neeraj Gill
  • 0 in reply to Neeraj Gill
    Prodigy 55 points

    Thanks for the response, I look forward to hearing back from the design team.

    By the way, I intend to operate the DAC5672A using 1:1 transformer AC coupled outputs, 20 mA full scale output current, dual bus mode, independent gain setting.  I intend to tie the clock and write inputs together externally as per the data sheet.

    In addition to the DAC5672A data sheet I also looked at the DAC5672 EVM document (slau139b). 

    Question:  If I use LVCMOS25 signals from an FPGA as clock and data signal inputs to the DAC5672A, I probably should not install any shunt resistors to ground on these lines, correct?  (the EVM schematic shows a 50 Ohm shunt resistor to ground on the clock input line and DNI on the input data lines)

    Question:  figure 17 in the data sheet shows the DAC5672A input digital circuit, would there be any benefit to reducing DVDD from 3.3V down to 3.1 or 3.0 V for use with LVCMOS25 inputs, and if I did this should I do the same for AVDD?

    Question:  what is the purpose of R9, R11, C7, and C8 in the EVM schematic? 


    Thanks,

    Chip

  • 0 in reply to chip
    TI__Mastermind 20541 points
    Hi Chip,

    1. Yes, you are correct you should not install any shunt resistors to ground on these lines.

    2. Yes reducing DVDD from 3.3v Down to 3.1 or 3.0 might help you but doing this may reduce the overall performance of part at higher clk speeds. You will have test that to see if you see any performance degradation at higher clk rate with 3 V dvdd. DVDD can be different than AVDD.

    3. R9,R11,C7 and C8 are all DNI.

    Regards,
    Neeraj Gill
  • 0 in reply to Neeraj Gill
    Prodigy 55 points
    Hi Neeraj,
    Thank you very much for answering my questions!
    --Chip