The LTC1555L provides power conversion and level shifting needed for low voltage GSM cellular telephones to interface with either 3V or 5V Subscriber Identity Modules (SIMs). The part contains a patented buck/boost charge pump DC/DC converter* that delivers a regulated VCCsupply voltage to the SIM card. Input voltage may range from 2.6V to 6V allowing direct connection to the battery. The output voltage may be programmed to 3V, 5V or direct connection to the VINpin.Internal level translators allow controllers operating with supplies as low as 1.425V to interface with 3V and 5V SIMs. A soft-start feature limits inrush current at turn-on, mitigating start-up problems that may result when the input is supplied by another low-power DC/DC converter. Battery life is maximized by 40µA operating current, and 1µA shutdown current. Board area is minimized by the miniature 16-pin narrow SSOP packages and the need for only three small external capacitors.ApplicationsSIM Interface in GSM Cellular TelephonesSmart Card Readers