In my current project setup I have a Li-Ion charger IC (the BQ25890 from TI) which manages the battery charging and discharging process. The charger IC has to power an ATmega328PB. The ATmega in turn controls a MOSFET to a high-current load in the 1-2A area. But most of the time, the ATmega sleeps in power-down mode, drawing only ~200nA of current. Even when it's active, it should not draw more than 0.1mA (+ the 1-2A of course) in average. To sum it up, a charger IC has to power a device which is always powered but draws minuscule current.
Now there's a problem, and this is why I ask.
I recently noticed a strange behaviour of my power bank, which cuts off current from a device with low current consumption. After reading a bit on the internet, this is not uncommon, and even a well-defined feature: The charger circuitry inside the power bank thinks it's leaking current and therefore cuts any small current off. With that in mind, I carefully checked the BQ25890's datasheet as I don't want such a feature for my MCU. However, I couldn't find nearly anything related to this besides the output voltage. These two values are suspicious:
- IBAT(LOAD) - Battery discharge load current - 15mA (min)
- ISYS(LOAD) - System discharge load current - 30mA (min)
These values are not further mentioned in the datasheet. If 30mA is the minimum current I have to draw, I would have to power the ATmega from a coin cell. Now these are my questions:
- Is my assumption correct the given values specify the minimum output current?
- Is my idea of using a coin cell generally better even if I can draw a small current out of the charger IC?
To give you a better understanding, I visualized my circuit configuration: