I'm in the very early planning stages of designing my first calculator using an AVR microcontroller. This will be my first project using a rechargeable Li-Ion battery (4.2V).
I'm having a hard time conceptualizing how I will be able to charge a battery using an external source (5VDC) while simultaneously using the calculator. You see this functionality all of the time in cell phones; as long as it's plugged into the wall, it will continue to increase in battery life despite using it at the same time.
As of right now, this is my very basic one-line diagram for the calculator.
As you can see, there is nothing between the battery and 5VDC 'wall' source that charges it besides the Charger IC. Right now the Charger IC that I'm looking to use is Unitrode bq2054. I don't see anything in the spec sheet that hints to a "use-while-you-charge" functionality.
My main question is - Am I missing something required to achieve this desired functionality? Does there need to be some interfacing between particular components? Is it sufficient to just leave the battery in parallel with a 5VDC source as it's charging and the calculator is turned on and being used?
I feel like there's some fundamental ideas that I'm overlooking here, but the question had to be asked.
Thanks in advance.