The first circuit we present consists of a step-down DC / DC converter with input voltage from 2.5 to 6.0 V and output of 1.8 V. This is the ideal circuit for applications that employ li-ion sources or batteries. The output voltage can be changed via an external resistive divider. In figure 1 we have the circuit, which suggested by Intersil (www.intersil.com). The circuit also has an automatic PFM / PWM control, or PWM mode only. When operating in PFM mode, the unloaded quiescent current drops to 120 uA. The typical PWM frequency is 1.4 MHz but can be synchronized up to 12 MHz. The operating mode is determined by the level of the SYNC pin. The ISL8010 integrated circuit used in this project is found in a 10-pin MSOP enclosure. More information about this circuit and other equivalents with Intersil components can be obtained in Application Note AN1209.
