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Silicon drift detectors (SDDs), due to their collection electrode geometry, have excellent noise performance and are well suited for low-energy X-ray spectroscopy applications. On the other hand these detectors, when dedicated to low energy X-ray spectroscopy, have a small sensitive area (from few square millimeters up to one square centimeter) to reduce the leakage current and its impact on the energy resolution. Because of this limitation they are rarely used in applications where large sensitive surfaces are required. We present the characterization of the spectroscopic performance of a very large sensitive area SDD (about 53 cm2) that has been realized in the frame of the LHC-ALICE experiment. We studied the energy resolution of the detector analyzing its dependence on both biasing conditions and temperature to evaluate the contribution of the different noise sources exploiting their relation with the shaping time. The experimental results obtained with 241 Am and 55 Fe sources show that the goal of a high energy resolution combined with large sensitive areas can be achieved.