What this boost converter does on your bench
The ADP1109AAN is a step-up (boost) DC-DC converter from Analog Devices, delivering an adjustable positive output from a 2V minimum input.
Output voltage range and setting it
The output is adjustable from 1.25V up to 9V, with positive output configuration. Setting the voltage is done with an external resistor divider.
What the 1.2A switch rating means for your load
The 1.2A switch current is the peak current the internal transistor can handle. That sets the maximum output power.
That puts it in indoor equipment, benchtop gear, consumer electronics, or office appliances. Not for under-hood automotive, not for a rooftop telecom enclosure in summer. If your board lives in a conditioned space, this is fine. The through-hole DIP package also means it's a natural fit for prototyping, breadboarding, or repair where you want to socket the part.