This paper proposed a light-load efficient DC-DC converter with dual-lower-bound hysteresis control and frequency control for always-on Internet-of-Things applications. The proposed dual-lower-bound hysteresis control allows the frequency to change dynamically according to the load current, which enhances the light-load efficiency. Fast transient response is also provided for wake-up events in IoT devices. A fully integrated 1/2 capacitive DC-DC converter is implemented in 180 nm CMOS process to demonstrate this concept. The result shows that a 77.3% efficiency is guaranteed over 100x load current ranges and an 80 ns active response time is achieved in 0.04 - 4 mA load transient.