A detector for the X-ray Correlation Spectroscopy (XCS) instrument at the Linac Coherent Light Source (LCLS) in Stanford (CA) is being developed at Brookhaven National Laboratory (BNL). The LCLS is the first operational X-ray free electron laser. It provides extremely bright coherent laser-like X-ray pulses with energy up to 8 keV, shorter than 100 fs and with a repetition rate that will go up to 120 Hz. An ideal detector for XCS experiments should cover a large angular range with high efficiency and provide a proper resolution to resolve the speckle. The requirement for dynamic range is not particularly stringent while a fast readout is needed. In particular, the Charge Pump Detector has to be highly efficient at the energy of 8 keV, provide a dynamic range of 100 photons and a readout noise much better than one photon. The 1024×1024 pixels have to be read within the repetition rate of the laser pulses, that is faster than 8 ms. The pixel size of 56 μm×56 μm is a compromise between charge sharing and small pixel. Working principle and details of the detector will be discussed.