Rework design for integrated charger/5V boost chip

[amcewen]

TI have a nice integrated battery charging and 5V boost chip that could replace both the charger and the 5V boost circuit.

Nice things about it are:

• 3.1A current from the 5V boost circuit, which would let us run more lights from it (currently it's ~1.5A IIRC, though that might include a bit of headroom so we're not running it at max output all the time)
• Fewer chips needed, so might be smaller
• Ability to charge at higher currents depending on USB charger attached

It'd be useful to compare the costs - I think it'll be more expensive than the current option, but it'd be useful to know roughly how much (so what's the total BoM cost for this circuit over the existing charger and 5V boost, inc. inductors, etc.); and maybe do a bit of a search through LCSC to see if there are any alternative all-in-one options. Presumably it's a fairly popular circuit, given how many USB power banks there are.

[huffeec]

Very ball park numbers gives a ~+$0.24 difference with this chip over the current setup. I've not managed to find anything equivalent on LCSC. (finding anything on LCSC is a challenge though so I'll have another quick look at some point)

Old
Battery management – CN3791 $0.5

• Power mosfet C308748 $0.25 Battery protection – FS312F-G $0.12 (discontinued at LCSC)
  • Mosfets FS8205 $0.18 (discontinued at LCSC)
    Boost converter – FP6276B $0.34
  • inductor – C27442 $0.16

Total - $1.55

New BQ25895M $1.79

[amcewen]

Dismantling one of the Pimoroni battery packs, they've got a protection PCB internally, so dropping the battery protection should be okay.

There's a 2.2uH inductor on the sample circuit for the new chip, but that shouldn't make a massive difference - there seem to be some on LCSC that are super cheap ($0.03!) and even if I'm missing some of the more important criteria (was just a quick search for shielded ones, at 2.2uH with a 3.5A+ current rating) they'll likely not be massively more expensive.

Might be worth a quick scan of Kicad to see if that throws up any alternative options; maybe Tindie too? But if we don't find anything cheaper I think a move to the BQ is worth doing.