I have put together the push button circuit explained in TI's SCEA048B application report with an under voltage protection using TI's LMS33460 chip. I ended up with the circuit attached.
The idea is to have the LMS33460 under voltage detector monitoring the +PACK line from the battery so it pulls down the regulator enable pin to power down the device in case the battery voltage falls bellow 3v, but I have several doubts:
After doing the schematic I realized that I should use an under voltage detector that triggers at 3.4v instead of 3v. I think this because the 3.3v LDO regulator has a maximum dropout voltage of 250mV and the TM4C123GH6PM has a minimum operating voltage of 3.15v, so 3.15v + 0.25v = 3.4v.. under this battery voltage the microcontroller will not have enough voltage supply. But, since I am using a 3.7v lithium battery, this would only give 3.7-3.4 = 300mV of margin for the battery to discharge.. I don't know much about lithium batteries but that doesn't seem to be a lot… is that a problem?
I haven't found the input resistance of the TLV70033's Enable pin in the datasheet, so how can I know the maximum pull down resistor (R33) to minimize consumption and still pull down the voltage to turn off the regulator. Anyway, this pull down resistor is not needed anymore after connecting the enable line to the flip-flop, since the flip-flop's output is not an open drain and it will command the line high or low without ambiguity, right?.
Do you think this would work? : )
Is there a better way for protecting the battery?