A voltage detector is handy for projects where you want to make sure your microcontroller doesn't run at a low voltage. For example, say you have a Feather Huzzah running on a lipoly battery every few minutes. Eventually the battery runs down, and goes below 3.3V, so the voltage to the ESP8266 core is too low, and could cause a lockup or corrupted data. Or maybe your battery is already drained and you're trying to charge it back up, but as you are trying to charge it up, the Huzzah turns on and the spike of current drains the battery immediately so it never gets through the trickle-charging stage.
This little chip is a simple solution: It monitors the voltage on one Input pin, and when that voltage goes below 3.3V, it will pull the Output pin low. If you connect that Output pin to the Enable pin on the Feather, it will make sure that the Huzzah does not run if the battery dips too low.
The KA75330 starts running at voltages as low as 0.8V so it'll be the first thing in your circuit that starts up. This little helper can really ease power start-up issues! Works best with microcontrollers and boards that have an Enable pin that is normally pulled high to enable function, and pulled to ground to disable.
This regulator requires at least 2,2uF electrolytic capacitors on both input and output for stability, just make sure your power supply already has those (it almost certainly does)!