The AST1S31HF from STMicroelectronics is a DC to DC Converter with Input Voltage 2.8 to 4 V, Output Voltage 1 0.8 to 4 V, Output Current 1 3000 mA, Operating Temperature -40 to 150 Degree C, Storage Temperature -55 to 150 Degree C. Tags: Surface Mount, Buck/Step down. More details for AST1S31HF can be seen below.