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AD5544 with AGNDx 1V above DGND?

Question asked by ggrau on Oct 5, 2015
Latest reply on Nov 5, 2015 by ggrau

Hi,

 

I planned to use the 4ch 16bit MDAC in a single supply environment (5V) to operate on an analog signal that is relative to a 1V reference. I thought I can connect the AGNDx pinx of the AD5544 to this 1V, DGND and VSS to GND, and VSS to 5V. The trouble is the "absolute maximum ratings" table which limits AGND to DGND to +-0.3V. I'm a bit clueless why the chip comes with 5 different AGND if I essentially can't put them anywhere but to DGND. From a different perspective I could run the DAC in dual supply but need the digital I/O refer to the negative supply.

 

Q0: The datasheet adds some confusion in talking about "GND" in the AbsMaxRatings which is not on any pin. I suppose "GND" should read VSS in this case (and not DGND)?

 

Q1: I assume the abs. max. of 0.3V is a true hardware limitation and AGNDx=1V won't work (as opposed to "not tested")? Looking at Q3 I can't believe that, though.

 

Q2: in a related discussion 54xx was suggested for single-supply use, but that is apparently available up to 12bit only and might not solve the issue. Any idea for a 4ch 16bit MDAC that works in a 5V single supply on an analog 1V intermediate ref?

 

Q3: thinking of a workaround with the 5544 (the DAC will be updated rarely): connecting DGND to a 1V clone and maybe use series resistors on the digital inputs to clamp the neg. low-level. Apparently the inputs are zener clamped to DGND and have already 5k in series - thus I wouldn't need external resistors at all. Did someone do similar or have a better idea?

 

thanks

  Guenter

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