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AD5686R Voltage Ref Accuracy

Question asked by ColinL on Nov 20, 2012
Latest reply on Mar 10, 2013 by DonWarr911
Hello,

 

Can someone please assist with these three questions?

 

We want to be able to adjust it for better accuracy, since the datasheet shows +/-2.5mV offset. Is it possible to use the Ref pin as a summing node so that we can inject a calibration voltage onto the pin to sum it with the internal 2.5V reference to provide a more accurate reference?

 

The datasheet says that the reference is on by default on power-up, and you have to turn it off by writing to a control register. If we use an external reference, then it would be fighting the internal reference during the time between power up and writing the control bit. And if you turn off the reference and don’t supply an external reference, then the chip won’t function. So I think it must be possible to drive the input pin while the internal reference is active. I’m hoping that this is acceptable and that this technique can be used to trim the internal reference. Or is there any other way to trim the D/A full scale?

 

  Also the chip only has one ground pin which is used for both power / logic and for analog output low reference. I’m wondering if instead of tying the Gnd pin to power supply ground it’s possible for us to drive this ground pin with an op amp, which we could then also adjust up and down by a few mV to provide calibration at the bottom of the scale. The op amp can of course handle current swings and magnitudes sufficient to handle the return current of the DAC.

 

Thanks

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