Hi Raja,
The minimum period is actually the maximum frequency. 2MHz is the fastest SCLK that can be used with the device. The SPI will timeout after 64 conversions cycles, so the next clock must happen before the 64 conversion cycles have completed. One conversion cycle is the period of time that it takes for the next conversion result to be ready. If the data rate is set to 5sps, for example, one conversion takes place every 200ms. 64 conversions take 12.8 seconds. 64 conversions at 2000sps (period of 500us) is 32ms.
Best regards,
Bob B