I have a project based on a Tinymesh radio module and a AtTiny2313 MCU, both running on 3.3V. Idle current draw will be 10-50mA. When transmitting radio packets (0-50 times a minute) the radio module draws about 400mA. I want to maximize reliability and operating time. Low voltage cutoff is not needed - uptime trumps saving the battery. I intend to power it from a single 18650 Li-Ion cell which as you know gives from 4.2 to 2.8V, i.e. a buck-boost function is needed.
Which regulator would be the best choice? Do I have to use the S7V8F3? The U1V11F3 is labeled as a Step-Up, but description says "switches to a linear down-regulation mode when the input voltage exceeds the output".
If both can do the job, what are the tradeoffs when choosing?