batteriesbattery-chemistryfuel-gauge
I'm working with the BQ27742-g1 (Texas Instruments) Fuel Gauge.
I have some confusion about battery parameters.
What is Qmax and Design capacity? Are they the same or different?
What is the configuration value for Qmax and Design capacity if my battery is single cell 4600 mAh?
What you are missing is the voltage. You're paying for energy storage, not for mAh. If you put n cells in series, the mAh does not change, but the energy stored is n times as much, because that's how much more voltage you have. Since they're in series the current (mA) through each is the same.
Some batteries are rated in W-h (watt hours) which is directly proportional to the energy stored (1 W-h = 3,600J),
It's just a bog-standard series-pass linear reg with with a FET instead of a BJT.
As @PlasmaHH notes, it is often used a pre-regulator in more sophisticate setups. It allows you drop some voltage (and thus power/heat) on an external element. Doing this also lets you extend the voltage input range of your more expensive IC regulator. TI has a separate appnote in which they suggest this.
This prereg idea (even with BJTs) not at all an uncommon. Cordless phones do this a lot for instance because they also use the [higher] pre-regulated voltage directly for a few components and they also derive a lower stable voltage for most of the digital parts. So in those setups it serves a double function (more bang for the buck).
Best Answer
Design Capacity 1000 mAh Set based on the nominal pack capacity as interpreted from cell manufacturer's datasheet. If multiple parallel cells are used, should be set to N * Cell Capacity
Qmax Cell 0 1000 mAh Set to initial configured value for Design Capacity. The gauge will update this parameter automatically after the optimization cycle and for every regular Qmax update thereafter.
Seems self-explanatory from the datasheet above