AnsweredAssumed Answered

AD1939 DAC outputs - Construction and Output current capability

Question asked by Luka_brazzi on Apr 9, 2014
Latest reply on Apr 15, 2014 by Luka_brazzi

Hi,

 

I'm going to use the AD1939 in a design where the differential to single ended output stage

is supplied by an assymetrical  0-8V power supply.

 

I would like to couple the DAC outputs in DC to the diff-to-SE stage, for which I

have an half-supply common mode voltage at 4V.

 

I start with the same schematic as the one presented in your evaluation kit for

which :

- I replace the OP275 by a low noise opamp that works with my supply and input

range conditions,

- I change the connection to ground of one resistor by a connection to a

low impedance 4V common mode. (see attached figure).

 

When I simulate this with my spice, where the DAC is replaced by two

symmetrical voltage sources having a DC common mode at 1.5V, I get

the functionality I am looking for. But...

 

... doing this, I ask the DAC outputs to absorb about 400uA DC ( (4V - 1.5V) / 2*3k).

 

Is this going to work ? Is this going to degrade performance ?

 

To further understand, can we consider the DAC outputs like OPAMP outputs ?

If yes how much current can we sink/source on these ?

 

Thank you for your support,

 

Igor

Attachments

Outcomes