DS2788 battery gauge for lipo batteries

[kasunt]

Hi all,

So I decided to go with this chip DS2788 which has a 1-wire interface to measure the battery voltages. It seems its adequate for my task and its not too pricey either. I also found a DS2788 Evaluation Kit by Maxim and their schematic isnt very clear and not easy to understand what the kit is doing. I don't have much knowledge about electronics but I guess you learn by getting your hands dirty.

Can someone please help me to get an understanding of the schematic ? I have attached the datasheet below. Its not easy to see the parts they are using either.

[kasunt]

Kind of figured out why P-channel and N-channel FETs are needs.

But do I go about calculating the sense resistor value ?

[bfritz]

So... You appear to only be looking at the datasheet for the EV-Kit.  I suggest you look at the datasheet for the DS2788 itself.

I think you'll find it explains many things:  http://datasheets.maximintegrated.com/en/ds/DS2788.pdf

Note that the datasheet explains how the circuit works, and what the is going on in the schematic.

As far as how do you choose a sense resistor value...

Think about the following:
What is the full scale voltage for the current measurement A/D?  (Start reading on page 8 of the datasheet mentioned above.)
What is the range of current you need to fuel gauge?  Most devices will never consume less than some lower limit, and will never go above some upper limit.  The resistor you choose needs to allow for all those currents to be measured.
In general a lower resistance sense resistor wastes less energy, while a higher value sense resistor makes it easier to measure low currents accurately.