I followed the data sheet and used the same Rset value (2Kohm) at FSADJ1 and FSADJ2. Therefore, no matter how the GAINCTRL pin is set high or low, the DAC1 and DAC2 have the same value full-scale currents.
In the experiment, I fed the DAC with a 1MHz cosine wave. When the GAINCTRL pin is set low, the DAC1 and DAC2 output swing are equal.
However, changed the GAINCTRL pin to high, the DAC1 and DAC2 output swing are unequal. The DAC1 swing level is unchanged, but, the DAC2 swing level is double !
Do you have any comment about this phenomenon ?