"but it doesn't stop the discharge" the componement do not stop the discharge of the battery at 3v but when it's dead at 2.5v
As mentioned, the atmega will reset at 2.6V due to the default brownout threshold.The 3.0 V comparator is a good idea. As I said earlier, the "best way" (as you put it) , is to have two sets of batteries and a DPDT relay that switches batteries when the one in use gets low and has a 680 uF cap to maintain the processor voltage during the 50 mS the relay is switching. That way you are always charging one while the other is in use. One half of the relay is to switch the arduino battery and the other half is to switch the battery charger from one battery to the other.
Can I replace LTC3335 by NCP1402?
The LTC3335 can. It's a buck-boost. You pay a little bit in efficiency, but you can have your cake and eat it too.
After thinking about it on the way to work , I realized that even if you only had one of each type you could still do it by putting the stepup first and step the voltage up to 6V, then use the stepdown to step it down to 3.3V.
That's one way to make a buck-boost.
Thank you for your helpThis time I have a buck boost regulator (I will use a LTC3531-3.3 because I want to reduce the size and the LTC3335 is a little bit big) but one line makes me affraid :"If the die temperature reaches approximately 150°C, the part will go into thermal shutdown and all switches will be turned off"Ok it will be turned off but 150°C is good ... for the cake but not for the gps (who is heat sensitive.The datasheet don't give a temperature vs V in curve... maybe it's can vary but reach 150°C
An other question : when the battery charge, the wire who is connected to bat + become - because the charge process invert the chemical reaction ?
I have just a last question :I searched in the mic834 datasheet the resistor values but I can't understand one thing"Programming the Threshold"I've understand there is a voltage divider for the threshold but my input voltage will vary between 4.20 and 2.9v also the threshold input voltage will vary too? Thanks you