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.

ADS5485 ext. reference voltage range

Other Parts Discussed in Thread: ADS5485

Hi all,

The ADS5485 does allow to add an external reference.

And I can find performance graphs for ext reference from 0.5V to 1.4V.

But what is the allowed range for the ext. reference?

thanks,

Katharina

  • Hi,

    I spoke with the characterization engineer about why the performance graphs run from 0.5V to 1.4V for VREF, and it was mainly a judgement call as to what range should be included before the performance drop-off makes it not worthwhile to push further.  As can be seen in the typical curves, as VREF is pushed higher the SFDR performace drops off.  This is due to decreasing headroom between where the circuits are operating and the supply voltage.  As you push VREF higher and consequently ask for the full scale range to be larger than 3V p-p, there is increased distortion as headroom to the supply voltage is reduced.  On the other side, the typical curves show that as the VREF is pushed lower the SNR performace rolls off.   But there is no hard limit on VREF min and max, we just chose to stop the data collection at 0.5V becuase the SNR degradation was pretty severe with full scale this small and we chose the stop the data collection at 1.4V because increased distortion was beginning to hurt SFDR too much.  But if you were to operate VREF outside of the range shown in the typical curves, you could but you can see what to expect for the performance drop-off in either direction. 

     

    Regards,

    Richard P.