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.