There are lot of material available over internet on this topic. I am suggesting you the books which I found useful (1 to 3 below). Also there are lot of application notes - 4 to 6 are something which are very basic. Hopefully they will be helpful to you.
1. Power supply cookbook ,2nd edn, Marty Brown, EDN Series
2. Switching Power Supply Design, 3rd edn, Abraham I. Pressman, Keith Billings, Taylor Morey, The McGraw-Hill
3. SWITCH MODE POWER SUPPLY HANDBOOK, 3rd edn, Keith Billings, Taylor Morey, The McGraw-Hill
4. Buck Converter Design, Design Note DN 2013-01 V1.0 January 2013, Infineon Technologies North America (IFNA) Corp., Infineon
5. Basic Calculation of a Buck Converter's Power Stage, Application Report, SLVA477A–December 2011–Revised August 2012, TI
6. Micrel’s Guide to Designing With Low-Dropout Voltage Regulators, Revised Edition, December 1998, Micrel Semiconductor