Complex sentence: Qualcomm announced it was developing a Snapdragon 820 at the 2015 Mobile World Congress, using Samsung foundries to manufacture the chip, whereas in the past it had used TSMC.
Split into simpler sentences: Qualcomm announced it was developing a Snapdragon 820 at the 2015 Mobile World Congress. It decided to use Samsung foundries to manufacture the chip, whereas in the past it had used TSMC.