In this paper, we present a blackout and brownout insensitive energy harvesting ASIC for ultra-low power autonomous sensor applications. It utilizes both RF or DC power inputs to deliver a regulated voltage for on-chip and off-chip devices. A voltage limiter has been integrated for overvoltage protection. As the ASIC utilizes two regulators alternately, a kick-start method has been used for switching the operation mode. The ASIC is implemented in a 0.18 μm CMOS process. It is able to use a wide range of input DC voltages (0.8…2 V at −40…85 °C) or input AC powers down to −14 dBm.