AD4001 and AD4005 differences

The AD4005 (1Ms/s) and the AD4001 (2Ms/s) are differential-input 16-bit ADCs that have identical conversion times. What (if any) are  the internal design differences between the two parts that allow the acquisition time to be specified as 290ns for the AD4001 but 2.7 times longer at 790ns for the AD4005?