Matthew Smith

Need guidance regarding LiFePO4 battery management parts

Discussion created by Matthew Smith on Mar 7, 2013

I am looking for a solution for solar powering of wireless sensors. I'm a digital guy and battery management is NOT my field of expertise, so I need a little (or a lot of) guidance here.

 

The devices in question would be operating 24/7, so the big question is what to do when the sun goes down. My original solution would be to trickle-charge a lead acid battery and then regulate down the battery/charging voltage to the 5V or 3.3V required by the device. However, this is quite impractical from the point of view of physical size and cost.

 

LiFePO4 looks to me to be a pretty safe and robust battery chemistry, and I can even get AA form-factor cells quite cheap, so can use standard hardware for mounting. Looking through the Freescale portfolio, I find parts like the MC34671 which is cheap, and simple to use. However, whilst this part will charge the battery for me, I need not just to charge the battery, but to power the system at the same time. This means that I would need to use some sort of separate switching system that would flip over to battery once the supply voltage were withdrawn. As the device could be powered by 3.3V, a simple arrangement of a pair of diodes wouldn't work, as the charging voltage of the battery would be greater than the regular supply.

 

TI has the BQ25070 which does the whole job in one part.Whilst I will do some experiments with this part, for ideological reasons, I want as many of the parts in the device to be from the Freescale portfolio. (Microcontroller and most sensors already are.)

 

If anyone can guide me to the most integrated, Freescale-based solution to this, I'd be grateful.

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