This brief presents a successive-approximation-register (SAR) analog-to-digital converter (ADC) assisted DC-DC buck converter, which operates in discontinuous conduction mode (DCM) and achieves fast load transient recovery characteristics. The power inductor of the buck converter uses the bond-wire inductance. During the load transient, the dynamic low-power SAR ADC samples the converter's undershoot/overshoot output voltage and controls the programmable current pump circuit to charge/discharge the output capacitor, thus speeding up and smoothing the load transient response. An additional compensation circuit is also designed to ensure the stability of the voltage mode control loop and the current pump. The chip fabricated in a 65-nm CMOS technology occupies an area of 1 mm2. The converter, switching at 100 MHz, achieves a peak power efficiency of 81% when $V_{IN}= 1.2$ V, $V_{OUT} = 1$ V and $I_{Load} = 50$ mA. When the load current steps from 2 mA to 50 mA, the measured undershoot/overshoot voltage is 101/92 mV, and the recovery time is 175/406 ns.