The LTC1695 fan speed controller provides all the functions necessary for a power management microprocessor to regulate the speed of a 5V brushless DC fan via a 2-wire SMBus/I2C interface. Fan speed is controlled according to the system's required temperature profile and permits lower fan power consumption, longer battery run time and lower acoustical generated noise versus systems that only provide simple on-off control for the fan. The LTC1695 incorporates a 180mA low dropout linear regulator, a 2-wire SMBus/I2C interface and a 6-bit DAC. Fan speed is controlled by varying the fan's terminal voltage through the output voltage of the LTC1695's linear regulator. The LTC1695's output voltage is programmed by sending a 6-bit digital code to the LTC1695 DAC via the SMBus. To eliminate fan start-up problems at lower fan voltages, users can enable the LTC1695's boost start feature that provides the DAC's full-scale output voltage for 250ms before decreasing to the programmed output voltage.