The DAC pass_band filter response is over 20Khz( in figure 10), while the DAC stop_band filter response is only over 2Khz(in figure 11) , who wants tell me why the gap is so large?
Evidently this is a typo in the datasheet. Figure 11 intends to show the filter's response above the audio range, so its 0 -- 20 KHz axis is in error. For example, it would make more sense if drawn like this:
The important fact is, the filter is more than enough for its job. Thanks to this DAC reconstruction filter, all we need after the DAC is a simple RC filter specified in the datasheet.