C and D versions differ in their ESD specification.
The ESD specifications, per HBM, are below:
MAX16910C ESD <= 2.5kV
MAX16910D ESD < 2kV
There are no parametric differences between these two options. The MAX16910D has a design fix that mitigates an incorrect start up event. However, it does have a lower ESD performance.
Currently, these are not specified in the data sheet but may be included in the future.