Question about LiPo battery + charge circuit

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Question about LiPo battery + charge circuit

Post by qwertymodo » Tue Jul 03, 2012 6:25 pm

I've read a lot about Li+/LiPo charging and the circuitry necessary for safe charging, and while I have a grasp on the general concept, I really can't figure out the specifics for the design I'm working on, so I figure this is a good place to come and ask. I mean hey, you guys build portable consoles, you're bound to know this stuff :P So anyway, I'm working on small project involving a bluetooth transceiver and a microcontroller (as small and cheap as I can get away with, I'm hoping to pull this off with an ATTiny, but I'm not entirely sure about that yet), and I want to power it with a battery. I saw this post on HaD ... o-systems/ where the guy is using a Maxim 1811 and an iPod Li+ battery, but in the last comment, somebody suggests the Maxim 1551/1555 for a self-contained charging IC. So looking around, I'm liking this battery ... -rate.aspx (though I may up the capacity depending on the life I get out of it), and I'm just wondering, if I use the Maxim 1551, is that the full package as far as charging safety circuit goes, or is it just a glorified regulator without the safety circuit, or what? Is that all I need, can I just go USB/DC->MAX1551->LiPo Battery leads, or is there more to it than that? Also, it's labeled "Polymer Li-Ion", so is that Li-Ion or LiPo? Thanks :)

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Re: Question about LiPo battery + charge circuit

Post by RDC » Fri Nov 30, 2012 5:59 am

If it has Poly in the name anywhere, then it's a LiPo battery.

I personally wouldn't recommend that battery, as it has no protection board built onto it. Look for one that already has that, as it's a requirement for that type of battery (it has this in the Tips section of that page there also) It's not going to take up much room at all with a built in one versus you having to make or install one.

The Max1551/1555 is fine and it's a complete charger IC, but not a substitute for the protection board that needs to be on the battery. The MAX chip there just needs 2 Capacitors installed is all, though it's charging time would be around 5 hours for that battery off the USB power. Battery Capacity, divided by Charging Amps, equals Charge Time, so that .500mAh battery / .100mAh USB charge current = 5 Hours to charge it, .500mAh / .100mA = 5h.

..or around 2 hours from the DC input of the MAX chip if it's used instead, since it charges at a higher rate when used, .500 / .280 = 1.78
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