A large acceptance and high magnetic rigidity spectrometer facility, SAMURAI is under construction at RIKEN. We plan to perform breakup reaction experiments that focus on the proton rich nuclei structure. The Si tracker needs to detect multiple nuclear fragments from the breakup reaction simultaneously. Atomic numbers of those fragments lie between 1 and 50. In the case of Sn breakup reaction, the energy deposition of fully stripped Z=50 fragment is 2500 times as large as that of Z=1 fragment. In order to realize such measurements, an amplifier with wide dynamic range of more than 2500 is required. Because it must operate under vacuum, it is necessary to minimize the amount of material. Therefore, we developed an amplifier IC which satisfies the requirements by implementing a square root gain response circuit.