Many proposals of pseudorandom sequence generators and stream ciphers employ linear feedback shift registers with dynamic feedback (DLFSR) as the main module to increase the period and linear span of the involved m-sequences. In this paper, we present a theoretical model that allows the design of longer sequences with higher linear span than in previous DLFSR schemes. The model determines the constant relationship between period and linear span for these structures. These more complex sequences here obtained improve the proposals based on LFSR with dynamic feedback found in the literature.