There are quite a few similar posts on this subject but I'm a little confused about the best way to proceed in my specific project. All my previous regulators have been linear types (eg: 7805, LM317 at best) - nice and simple. For me anyway.
The project I'm working on needs 3 voltage outputs from a Lithium (lipo or li-ion) battery - 3.3V, 5V, 12V.
- 3.3V @ 500mA (estimated) main rail for the ARM based system on module. ARM can be at full power, standby, or off. This requirement doesn't look too onerous. Stackexchange has some good posts in this area.
- 12V @ 250mA for sensor system A. Switchable from the ARM (or a PIC or some such).
- 5V @ 2.5A for sensor system B. Switchable from the ARM.
Plus the battery needs to be recharged. I can use one or two cells although it might not be up to me. Two cells might be easier given that I can boost to 12V and derive 3.3V and 5V from the 8.4V line.
I'm not sure about the best way to proceed as there's a blizzard of chips out there. I was hoping someone has used a nicely behaved one that combined charging and regulated outputs. For example, Microchips MCP7383 can charge LiIon fine and a chip like the TPS63020 is a buck/boost regulator to give you 3.3V but other chips combine the charger and the regulator which seems a better idea.
If I use a single cell LiIon I get 3.4/3.5V to 4.2V. Is that too tight for 3.3V, especially given the power draw when I turn on the 5V boot circuit. Should I first boost to 5V and use that to get 3.3V? And then use another boost to 12V?