Why does the AD7294 have a seperate internal DAC and ADC reference?
The AD7294 has a separate ADC and DAC reference so that noise on one reference due to either converter will not affect the accuracy of the other converter. Ideally, the two separate internal references should be used. If the two references are shorted together one of the references should be powered down in the Power-Down Register. A separate 220nF decoupling capacitor should be used on each of the references. Either internal reference on the AD7294 can be used elsewhere in the application once it is externally buffered. On power-up, the AD7294 is configured for use with an external reference. To enable the internal references, write a zero to both the D4 and D5 bits in the power-down register (see the Register Setting section of the datasheet for more details.)