SLVSBY7 February 2017 DAC8775
There are three possible hardware power supply configurations for the DAC8775: the internal DC/DC provides both positive and negative supply voltages, the internal DC/DC provides only one of the supply voltages with an external supply provided on the other, or the internal DC/DC is not used at all and external supply voltages are provided for both positive and negative supply voltages. Simple illustrations for each case are shown below.
Figure 136 illustrates using a single supply from the DAC8775 internal DC/DC and the other supply from an external source. In this example the VNEG_IN_x supply is the input being supplied by an external supply, or ground for unipolar output spans. A similar scheme could be used if VPOS_IN_x was supplied by an external supply and VNEG_IN_x was supplied by the internal DC/DC.
The scheme in Figure 137 should be used if the internal DC/DC is not used at all and external supplies are selected for VPOS_IN_x and VNEG_IN_x. When using external supplies for VPOS_IN_x it is important that VPOS_IN_x, PVDD, and AVDD nodes are tied to the same voltage potential with the same ramp-rate.