After reviewing the datasheet it become unclear as to what an acceptable VDD_EXT could be. they give specs for 1.8V and 3.3V, but can it be 2.8V? It is understood that the VDD_INT = 1.1V.
Only 1.8V and 3.3V nominal ranges, for this family.
the two value 1.8V and 3.3V ，or the range from 1.8 to 3.3 ？
We only test at 1.8V nominal and 3.3V nominal (plus a small guardband around these voltages). We don't test for any nominal voltages in between 1.8V and 3.3V VDDEXT, so I'm afraid we can't guarantee operation at 2.8V VDDEXT.
Retrieving data ...