Hi, in the datasheet of AD9744, it states that REFLO should be connected to ACOM for both internal and external reference operation modes. However in the reference designs (SOIC), it says that if you want to use external REFIO, you should tie REFLO to AVDD. I search some other documents such as AD9708 and AD9754, they all say that if you want to use external REFIO, you should tie REFLO to AVDD to disable internal VREF.
So, for AD9744, if I want to use external VREF, where should I connect REFLO to ? AVDD or ACOM ?
The design of the internal reference was changed slightly in the third generation TxDAC AD9744 such that REFLO should always be tired to ACOM. To use an external reference you just overdrive the internal reference's output current source which I think is about 200 uA.