ST1S10 is monolithic synchronous step-down regulator able to provide 3A of output current and it is working at 900Khz frequency. The device operates with an input voltage range from 2.5V to 18V and provides an adjustable output range. It can operate either at 900KHz or from an external clock. The high switching frequency allows the use of tiny SMD external components. youritronics.com published an spreadsheet calculator made on OpenOffice Calc and saved as XLS. You have to enter the requested values on brown boxes and you’ll get the result in the yellow boxes. Download the calculator on the link below.
ST1S10 calculator - [Link]