Circuit activity is a function of input patterns. When circuit activity changes abruptly, it can cause sudden drop or rise in power supply voltage. This change is known as power droop and is an instance of power supply noise. Although power droop may cause an IC to fail, such failures cannot currently be screened during testing as it is not covered by conventional fault models. In this paper we present a technique for screening such failures. We propose a heuristic method to generate test sequences which create worst-case power drop by accumulating the high-frequency and low-frequency effects. The generated patterns need to be sequential even for scan designs. We employ a dynamically constrained version of the classical D-algorithm for test generation, i.e., the algorithm generates new constraints on-the-fly depending on previous assignments. The obtained patterns can be used for manufacturing testing as well as for early silicon validation. A prototype ATPG is implemented to demonstrate the feasibility of the approach and test sequences are generated for ISCAS circuits.