Analogue control of monolithic DC/DC converters is coming to a limit due to high switching frequency and a request for large regulation bandwidth. Digital control is now experimented for low-power low-voltage switch-mode power supply. Digital implementation of analogue solutions does not prove real performances. Other digital controllers have been experimented but applied to discrete converters. This paper compares a classical digital controller to a possible alternative strategy. Sensitivity functions are used to compare controller performances. RST algorithm determined by robust pole assignment shows better performances