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 ?
Anyone could answer this question ? or should I made a backup that the REFLO pin can be connected either to AVDD or AGND ?
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.
Thanks! I think the reference schematic of AD9744 should be updated accordingly I found that Agilent 33220A (which uses AD9744) tied REFLO to AVDD, is there any drawbacks in doing so ? should I leave a backup plan where REFLO are tied to AGND via a 0Ohm resistor and a DNP resistor pulled to AVDD?
The internal functioning of the REFLO and REFIO pins was changed to allow certain "test" modes used during final test in the factory. Agilent is going against our recommended use of this pin on the AD9744.
In an official FAQ of analog, AD9748_REFLO pin
it says that the REFLO should be connected to AVDD, I am confused now. Where on earth should the REFLO of AD9744 be connected to?