This paper presents a new automatic pattern generation methodology to stimulate the maximum power supply noise in deep submicron CMOS circuits. Our ATPG-based approach first generates the required patterns to cover 0 → 1 and 1 → 0 transitions on each node of internal circuitry. Then, we apply a greedy heuristic to find the worst-case (maximum) instantaneous current and stimulate maximum switching activity inside the circuit. The quality of these patterns were verified by SPICE simulation. Experimental results show that the pattern pair generated by this approach produces a tight lower bound on the maximum power supply noise.