Hello Marc,
The ADS9120 supports enhanced SPI. One of the most useful features of enhanced SPI is Data Transfer Zone 2. If you operate in Data Transfer Zone 2 (Section 7.5.2 of datasheet), you can achieve the full 2.5Msps data rate with 16b data transfer and an SCLK frequency of 45MHz using only one SDO line.
In Data Transfer Zone 2, you have almost the entire cycle period for the SPI transfer, minus a quiet time. For the ADS9120, the total quiet time is 35nS. For a 2.5Msps sample rate, the cycle time is 400nS resulting in a SPI transfer time of 400-35=365nS, which provides enough time for the transfer of the 16b data conversion result using an SCLK = 45MHz.
You can also reduce the sample rate; there is no minimum sample rate for the ADS9120, which will also further reduce the maximum SCLK needed.
Regards,
Keith N.
Precision ADC Applications
