I'm looking for a device which monitors a 3.3V line. When the line drops below, say, 2.7V, I would like it to switch power over to a battery backup (3V lithium coin cell.) It would also be good if it provided a logic signal to alert of the supply failure so the MCU in my project can switch over to a low power mode. It needs to be able to switch up to 120mA when the supply is high. What is the name of this device? I have a feeling it's quite common in applications like laptop computers.
Ideally it would have 5 pins: Vin main, Vin backup, GND, Vout, Logic out.
Best Answer
Power Management Controller / Power Management IC
The functionality your after would normally be part of a full system power management IC or a battery charging/management IC.
If all you need to implement is exactly what you asked for, a single FET with a low Drain <-> Source voltage drop and maybe a couple resistor to set the trip point are all thats required.
If you need to smoothly handle bounce, such as the bounce that occurs when you plug in a DC barrel jack, you can use a supervisor/reset controller designed to deal with bounce and use the reset output to trigger the FET.