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Boost converter + lipo charger/battery protection circuit
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aiq25:

--- Quote from: janoc on March 19, 2019, 01:59:03 pm ---Uh careful - those BQxxx chips only provide a USB OTG boost converter function (aka if you activate the function, you will get 5V/1A out of the normally input Vbus pin to power any device that could be connected to e.g. a smartphone). Otherwise they work as a sort-of buck converter when you have charger connected. If the battery is too discharged or not present the IC will regulate the output voltage to about 3.5V minimum, otherwise it keeps the output at battery voltage + 150mV (or so) - so the output is not really regulated and moves as the battery voltage changes. When running without the charger, the output isn't regulated at all, i.e. no buck or boost functionality (ignoring the OTG thing).

The datasheet is a very confused mess with quite a few contradictory parts but when you look at the block diagram of the IC it is clear what it can actually do.

--- End quote ---

Thanks. Yeah I was reading the datasheet carefully and I searched one of those parts and found a link to a TI forum where they recommend separate boost and charger IC's. I think that's what I will go with.
kjr18:
I made one of those charger/protection/boost modules some time ago, and I came up with something like this. It uses smaller and less powerful version of TP4056, because I wanted smaller board size. When no usb is connected, transistor is open, allowing boost circuit to use battery for source, when usb is connected, mosfet closes and boost uses usb source with some voltage drop on Schottky diode. It's simple and works. You could also use two diodes, but that would give you some voltage drop on battery, thus limiting energy stored in it.
janoc:

--- Quote from: aiq25 on March 21, 2019, 04:20:26 am ---Thanks. Yeah I was reading the datasheet carefully and I searched one of those parts and found a link to a TI forum where they recommend separate boost and charger IC's. I think that's what I will go with.

--- End quote ---

You can still use the BQxxx part for the charging side - if you want fast charging from USB using the various charging specs (BC, PD, the various non-standard resistor dividers between D+ and D-) and dynamic power path management (charging while using the device, weak charger supplemented by the battery, works even with no battery, etc.) these chips are hard to beat on price and board space. There are simpler solutions using a few discrete components but none of those will give you the fast charging and the charger flexibility (available current/voltage detection) that this IC series can do.

Just add another converter or LDO after it to generate the power rails your project requires.
janoc:

--- Quote from: kjr18 on March 21, 2019, 08:39:53 am ---I made one of those charger/protection/boost modules some time ago, and I came up with something like this. It uses smaller and less powerful version of TP4056, because I wanted smaller board size. When no usb is connected, transistor is open, allowing boost circuit to use battery for source, when usb is connected, mosfet closes and boost uses usb source with some voltage drop on Schottky diode. It's simple and works. You could also use two diodes, but that would give you some voltage drop on battery, thus limiting energy stored in it.

--- End quote ---

That's pretty much what you will find in many of those cheap battery + 5V boost AliExpress modules, except for the battery protection circuit (most Li-ion/Li-Po batteries have these built-in, you aren't using raw cells, are you?).
kjr18:

--- Quote from: janoc on March 21, 2019, 09:30:28 am ---
That's pretty much what you will find in many of those cheap battery + 5V boost AliExpress modules, except for the battery protection circuit (most Li-ion/Li-Po batteries have these built-in, you aren't using raw cells, are you?).

--- End quote ---

Yeah, but if you need other voltages, then you might be out of luck. I made this mainly for powering DSO150 (which gets powered by around 9V). Works ok for this purpose. I added battery protection just in case if I ever wanted to use bare cell.
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