Synchrotron applications such as coherent X-ray diffraction and X-ray photon-correlation spectroscopy require detectors with a pixel pitch of 50 m as highlighted by a survey with beamline scientists of Diamond Light Source synchrotron. Furthermore, the detector should also have a high frame rate, large dynamic range and large detection efficiency. The Medipix3 readout chip with a pixel pitch of 55 m emerged as a good candidate to develop a new detector for the aforementioned applications. Additionally, it implements a new operating mode, referred to as Charge Summing Mode (CSM), with the purpose of eliminating charge-shared events. This mode can be very useful in this case, since the charge-sharing effect increases as the detector pixel size decreases. Also, its design is expected to be more radiation hard that its predecessor Medipix2. The present work focuses on the evaluation of the radiation hardness and the CSM operating mode of a Medipix3-based detector in order to develop a large area detector for synchrotron applications.