i am using AD7899 14-bit ADC.. i am getting unique result for a constant input voltage.
Have you tried grounding input pins and reading conversion data? You should expect the reading to be all zeros. Please see table 3 on page 10 of the datasheet. We don't usually use regulated power supplies on our inputs so we need to isolate that. Since the 1 LSB of the AD7899-3 is 610.4uV, we use very precise instruments for inputs as well.
Thank you for using ADI parts in your application. How are you using the AD7899? Can you specify the unique results you are seeing?
i have given 1.69v at ADC input. every time when i try to read the resultant digital value, the result having the tolerance of +or - 100mV. i tried with both BUSY and EOC methods.
What reference did you use? Is it the part's 2.5V reference or did you have an external reference? Can you share your schematic diagram so I can take a look?
i shared my schematic. and i used internal reference of 2.5V as a reference..
Durga Lakshmi K
Thanks, Durga. I'll give your schematic a look. Meanwhile, can you tell me what you are using for your input signal?
i am giving DC -2.5V to +2,5V as input. to
i am giving DC -2.5V to +2,5V as input. to AD7899
I assume you are using the AD7899-3 with analog input range of +/-2.5V. This version has an LSB of 610.4uV. So you are getting codes that are off by ~165LSBs, am I right? Can you tell me what is the source of your input signal?
Also from the datasheet, the /STBY input is a logic input which must be high for normal operation. Can you try to connect this to your VDRIVE instead of VDD?
As above, what's your input source? Are you buffering your input to the ADC?
Are you leaving the part fully powered up between conversions, or powering down?
You could try applying 2.5V to the reference to overdrive the internal ref. This would rule out a reference issue.
i am applying single ended voltage as input...(-2.4V to +2.4V).
i am getting same responce from after connecting /STBY to VDRIVE instead VDD.
and the internal Vref is always showing constant voltage of 2.49V even ADC.
What equipment did you use for your single-ended input voltage of -2.4V to 2.4V? What is the resolution of the meter you used to measure the Vref?
i am applying voltage from regulated power supply. and my measuring equipment has 1mV of resolution.
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