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supply voltage vs. output/input voltage on DACs and ADCs

Question asked by jnewman6 on Mar 10, 2013
Latest reply on Mar 11, 2013 by Padraic

Hello,

 

I am interested in using AD5686R and AD7682 for a lightweight analog data acquisition system. Right now, I am thinking about how to properly power these devices. One of my design constraints is that the device must be powered by a wall wart with a +5 volt  output. I was thinking that I would pass this through a LDO regulator to get a clean supply rail. However, even with the lowest dropouts, the best I can do is get ~4.8 volts to the supply pins of the converters. According to the data sheets, the converters must have the following voltage supply ranges:

 

AD5686R: 2.7-5.5 volts

AD7682: 2.3-5.5 volts

 

so, I am right in the sweet spot with my regulated 4.8 volt supply.

 

Here is my question: The AD5686R generates a internal 2.5 volt reference and, using  a gain factor of 2, allows the chip to have a 2*VREF = 5 volt swing on its output pins. If I use the device in this mode while only supplying 4.8 volts, will I be limited to a 4.8 volt output instead of the full 5 volt range? Is this also the case for the AD7682 in terms of the swing of its inputs? If so, I suppose I can use an external reference voltage.

 

Thanks.

 

-jon

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