An input-output regulated adaptive ramp ($\mathrm{IOR}^{2})$ for fast load transition of pulse width modulation (PWM) buck convertor is presented. The scheme employs an adaptive ramp regulated by input and the voltage from the error amplifier to achieve fast load response and low line and load regulation rate. Simulation shows that an under/overshoot voltage of −32 mV and 35 mV, with $8 \mu$ and $8.3 \mu \mathrm{s}$ recovery time are respectively obtained for the load current stepping between 1 A and 1.7 A. The line/load regulation rate is respectively $12.4 \mu \mathrm{V} / \mathrm{V}$ and $1.04 \mathrm{mV} / \mathbf{A}$. Implemented in a $0.25 \mu \mathrm{m}$ BCD process, the proposed IOR² PWM regulator is capable of converting input voltage of 5 V to 65 V to output range of 3.3 V to 60 V with adjustable switching frequency up to 2.2 MHz, showing a peak efficiency of 94.5% at 1 A load current.