This paper proposes a switched-capacitor circuit that can detect power SCAs by intrusion detection of a current sense resistor in the external power supply line. A pulsed current is pulled on the supply line to introduce a voltage difference proportional to the IR drop. This IR drop is then amplified through a parasitic-insensitive switched-capacitor amplifier and compared against a pre-determined threshold. The circuit achieved a 4.01us typical detection time and better than 72% accuracy, consuming 2.97 mW in 65-nm CMOS. This work is the first mixed-signal IC implementation for power SCA detection.