The ADP1109AAR-5 is a fixed 5V step-up (boost) DC-DC converter from Analog Devices, designed to generate a regulated 5V rail from a lower input voltage. It integrates a 1.2A switch and switches at 120kHz, suiting it for battery-powered or low-voltage rail applications where a clean 5V output is needed without an external pass transistor. The input range spans 2V to 9V, so it can run from two alkaline cells, a single Li-ion, or a 5V bus that needs a regulated boost. The single positive output is fixed at 5V, which simplifies the BOM — no external feedback divider needed. No synchronous rectifier is used, so expect slightly lower efficiency at light loads compared to newer parts, but the simpler topology keeps the external component count low. Packaged in an 8-SOIC, this is a surface-mount part for standard PCB assembly.
The 1.2A switch current rating is the peak current the internal power transistor can handle. For a boost converter, the input current is higher than the output current.
Note that the part is RoHS non-compliant, so it is not suitable for builds requiring RoHS exemption-free compliance. For RoHS-compliant alternatives, the ADP1111 series (e.g., ADP1111ARZ) is a surface-mount option, though it uses an adjustable output and a lower 0.4A switch.