37.6.3.3 Conversion Time
The time needed to convert a value depends on the selected OSR, PRESCALER and on the frequency of the SDADC.
For example, a sigma-delta converter running at CLK_GEN_SDADC = 1MHz with program the OSR of 64 and PRESCALER of 0. The output sampling rate equation is CLK_GEN_SDADC/(OSR * PRESCALER * 4) which means to converts data every (64*2*4)/1e6= 512μs. The output data rate is then 1.953ksps.
Note: The CLK_SDADC_PRESCAL clock range is CLK_GEN_SDADC/2, if PRESCAL is 0.
The OSR and PRESCALER are described in the CTRLB register.