Grand Central running on LiPo?

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jmacarthur
 
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Joined: Thu Dec 08, 2016 11:46 am

Grand Central running on LiPo?

Post by jmacarthur »

I've got a possible application for an M4 Grand Central, but it needs to (sometimes) run from a single-cell LiPo battery. My tentative plan is to drive both the Vin and the 5V line from the LiPo. The 3.3V regulator has a dropout voltage of 250mV under full load, so that's 3.55V at the battery, which is reasonably depleted.

I'm mostly worried about the LiPo trying to drive the USB 5V. With the LiPo driving Vin, MOSFET TR1 _might_ disable, but with the voltage divider of R1G$1 and R1G$2, a depleted battery might not shut the MOSFET off all the way, resulting in USB trying to charge the battery, to the detriment of both.

A safer approach would be to detect USBvcc (unfortunately not brought out to any headers) and use it to disconnect the battery.

Anyway, anyone try this yet?

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adafruit_support_mike
 
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Re: Grand Central running on LiPo?

Post by adafruit_support_mike »

You can use a small charge pump to provide 5V, and connect a regulated 3.3V to the Grand Central's 3.3V pin:

https://www.adafruit.com/product/3661
https://www.adafruit.com/product/2745

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