Can I connect inputs on AD667 directly to digital outputs on Atmel SAM3X8E ARM Cortex-M3 CPU?

I'd like to connect the 12 ea. digital input lines on one of your DAC AD667 chips directly to the digital output lines on an Atmel SAM3X8E ARM Cortex-M3 CPU. Will that work, or do I need to use some type of level-shifting to accommodate Atmel's 3.3V logic? Thank you. #JMLQ1 

  • 0
    •  Analog Employees 
    on Feb 23, 2017 2:47 AM

    Hi:

    The AD667 DAC was designed back in the early 1980's ( it just so happens I'm the original designer ) and the digital logic inputs were designed to have the standard 5V TTL logic threshold of 1.25 V. This threshold voltage is fairly well defined ( regulated ) and generally does not depend on the + or - supply voltages applied to to the AD667. The data sheet specifies a maximum logic "0" voltage of 0.8 and a minimum logic "1" voltage of 2.0. The digital input pins sink a much smaller than std TTL input current of 10 uA or less so the load on any driver will be slight.

    The question of if a 3.3 V CMOS output driver will work or not will depend on exactly how high the output actually goes under all possible cases of supply ( 3.3V +/- ? ), and temperature and will it in all cases be more than 2.0V ( logic"1"). The CMOS driver should have no problem driving the input to less than 0.8V ( logic "0" ).

    As I said the AD667 was designed and is guaranteed to be TTL compatible. It might work under other cases but as they say "your mileage may vary".

    Doug

  • Doug,

    I really appreciate your feedback regarding the AD667, and I'm wondering if it would be okay to ask your opinion about something else.  

    1. What Analog Devices DAC would you recommend that has similar specifications to the AD667 (i.e., all-in-one and easy to use) but has only 8-bits of resolution (instead of 12)?

    2. Is there a DAC similar to the AD667 (8-bit and/or 12-bit resolution with +/- 5V output), but is designed for 3.3V CMOS signal levels instead of TTL?  

    3. Could you please recommend an Analog Devices multiplying DAC (10 or 12 bit resolution) that's easy to use, has voltage output (+/- 5V), has its own internal reference, and will accommodate approximately 1 MHz signals?

    4. Last question: what is a high-quality reasonably priced general-purpose Analog Devices Op Amp that will accommodate approximately 1 MHz signals? (Perhaps available in a quad package.)

    Sincere thanks, Doug.

    Jim Laird

    Tucson  AZ 

  • 0
    •  Analog Employees 
    on Feb 24, 2017 1:32 AM

    Hi Jim:

    ADI makes far too many voltage output DACs for me to try to sort though to answer your requested requirements. I would suggest you try looking though the product selection tables for DACs that meet your needs.

    Again the op-amp product selection tables would be a good place to go to sort though the many op-amps ADI offers.

    Doug