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I am working on a project which will be powered by a single lithium ion cell that is boosted to 5V with a MCP1640 boost IC. It will sometimes be connected via usb, and I would like the circuit to automatically switch to usb power when it is plugged in. The MCP1640 has an active high enable pin, so I was thinking I could use the enable pin to switch the circuit from battery power to usb. Would it work if I were to use a NOT inverter IC like (http://uk.rs-online.com/web/p/standard-logic-gates/7705351/) to put a low input signal into the MCP1640 enable pin when USB 5v is input into the inverter IC so that the boost IC is shut down when the usb is connected? Thanks in advance for any advice!

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What you are looking for is called PMIC - Power Management IC. The MCP1640 is a weaker version of real PMIC. Several companies (Linear, Texas Instruments, Cypress) offer a whole line of ICs that are charging a Li-Ion battery when external power is available (while feeding the system directly), and automatically turn to battery booster when external power is lost. These circuits also can limit the power they take from USB in accord with the standard, and some even might negotiate power within BC1.2 specifications. As an example, take a look at this IC, BQ24296. It is likely that you will find a better fit to your particular need from the sizable lineup of their products.

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  • \$\begingroup\$ Wow, that IC does look very capable for what I need. In my case however, I am still a beginner in electronics, so I would like to try to keep things as simple as possible. While it would be best to use a PMIC like that, I already know how to use the MCP1640, and I have a charger and protection circuit that I know how to use as well. In the future I will definitely try to use a PMIC like that though. \$\endgroup\$ – Eric Navarrete Jul 19 '17 at 1:27
  • \$\begingroup\$ @EricNavarrete, try their "designer". It might show many more variants, I2C controlled or stand-alone. \$\endgroup\$ – Ale..chenski Jul 19 '17 at 1:50
  • \$\begingroup\$ There are a ton of ICs, but I couldnt find one which was standalone that also had a 5v boost converter built in. I will keep looking though. I think for this current project I will just leave the boost converter IC always on and add schottky didoes to the usb and boost converter outputs and connect them together. \$\endgroup\$ – Eric Navarrete Jul 19 '17 at 11:19

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