• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 46 subscribers
  • Views 468 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Would it be possible and sugjestable to use a 3.3v supply and power the ads1278 with it?

josh wojnas
Intellectual 805 points
Other Parts Discussed in Thread: ADS1278, THS4521, OPA1632

Would it be possible and sugjestable to use a 3.3v supply and power the ads1278 with it?

The voltage would be devided and output on vcom then buffered for 1.5v center signal for the baseline.

Then the 3.3v could be devided in half for 1.65v for the digital core of the chip.

What regulator or circuitry would be nessisary to have this work with the fullest number of avalable bits?

Could I use the ft2232 for the 3v reference with enough precision to get all the bits of acuracy? could I use simple filters to allow the analog supplys to not be bothered by the digital?

my current schematic has lots of powersupplies and references it is known as adc4.

http://sites.google.com/site/openloopproject/

 

  • 0
    TI__Genius 17905 points

    Josh,

    The Electrical Characteristics table on p.5 of the ADS1278 datasheet states that AVDD must be between 4.75V and 5.25V. This is the AVDD range for which the part has been designed and has been tested. There might be a gray area at the upper and lower limits, for example, at 4.74V or 5.26V, but 3.3V is far below the minimum specification. It is doubtful that the part will work properly, if at all, with an AVDD that low.

  • 0
    TI__Mastermind 43915 points

    Josh, 

    I am a little confused on what modifications you are planning to make to your current schematic. Are you asking if you can set the AVDD to 3.3V, the IOVDD to 3.3V and the DVDD to 1.65V? If so, I would urge you not to do that. The ADS1278 needs an analog power supply in the range of +4.75V to +5.25V in order to properly power the analog portion of the IC. If you are planning to power the AVDD from +3.3V, then we cannot guarantee the ADC performance. 

    How are you planning to drive your inputs? I recommend you look at how we designed our EVM. The reference must be very precise and stable with minimal temperature drift. I looked for the specs of the 3.3V reference from the ft2232 and was unable to find anything on the stability and drift. Look at the User's Guide to see how we designed the reference voltage and how we drive inputs. Recently we have also been using the THS4521 op amp in place of the OPA1632 in order to stay away from a +/-15V op amp to drive a 5V part. 

    http://focus.ti.com/docs/toolsw/folders/print/ads1278evm.html

    Your layout is also going to be very important to get maximum performance from your ADC. Make sure that your digital and analog portions of the layout are well isolated from one another (this includes keeping the digital and analog supplies separated). Also, focus on having a clean ground plane that is connected to both your digital ground (DGND) and analog ground (AGND). You may also want to have 10uF capacitors close to the AVDD power supply pins.

    Regards,

    Tony Calabria