An input-output regulated adaptive ramp for fast load transition of pulse width modulation buck convertor is presented. The scheme employs an adaptive ramp regulated by input and the voltage from the error amplifier to achieve fast load responses and low line and load regulation rate. Experiment shows that an under-/overshoot voltage of -32mV and 35mV, with 8µs and 8.3µs recovery time are respectively obtained for the load current stepping between 1A and 1.7A. The line/load regulation rate is respectively 12.4µV/V and 1.04mV/A. Implemented in a 0.25µm BCD process, the proposed IOR2 PWM regulator shows a peak efficiency of 94.5% at 1A load current.