AD5440 AGND

Hi, 

Are you referring to this document? AD5428/AD5440/AD5447 (Rev. D) (analog.com) I'm not seeing this description. 

Best regards,

Ian

The exact description is as follows:

"DAC Ground Pin. This pin should typically be tied to the analog ground of the system, but can be biased to achieve single-supply operation."

For example, is it okay if VDD = 3.3V, VREF=-10V,DGND = 0V, AGND ≒ 0V,?

Your example should work. 

This DAC is designed to operate with either negative or positive reference voltages, as shown in Table 1. Reference Input Range spec. The VDD power pin is only used by the internal digital logic to drive the on and off states of the DAC switches.

Best regards,

Ian

thank you for your answer.
However, in the circuit diagram of fIG38, it does not work at VDD = 3.3V, VREF = -10V, DGND = 0V, AGND = 3.3V, and it is normal at VDD = 3.3V, VREF = -10V, DGND = 0V, AGND = 0v. It worked.

Therefore, I think that there may be some restrictions on AGND.

Is there a condition between AGND and DGND or VDD?

What operation or output are you trying to achieve with AGND=3.3V? As mentioned, there is no problem with biasing the AGND pin but with this, the output transfer function given for the Figure 38 is no longer valid if AGND is not at 0V.