Hi All,
I found this circuit that allows for the use of a momentary push button to power on an arduino and then the arduino provides the "hold" signal to continue the power latching on.
I have an application where I will have a ~12V input power from (3) 18650 batteries in series. Unfortunately there are a few components not rated for this type of input voltage (max 8V).
I have tried to find equivalent components with a higher input voltage... so I replaced the TPS27081A with a Si3865DDV... same foot print and pinout...
I also replaced the P channel mosfet FDV302P with BSS84 so that the max GS voltage is above 12V.
I think that should do it... however, based on the circuit in the link I provided it would seem that when the pushbutton is pressed and the p-channel mosfet gate is pulled low, the "BTN" line that would go to the Arduino would see my battery voltage of ~12V ? It would also seem that pin 5 (ON/OFF) of the TPS27081A (or in my case the Si3865DDV) would also see the 12V ? Am I understanding this correctly? I don't want to fry either of them...
The Si3865DDV ON/OFF pin is only good to max 8V on the datasheet...
If anyone can help me out with these few details I would really appreciate it!
Thank you
Step the battery voltage down to 5v with a mini buck converter before the circuit.
But then the buck converter would always have to be running and it would be draining the batteries when not in use. Unless it went somewhere between the p channel mosfet and the Si3865DDV but then its only purpose would be to step down voltage for the button push... a lot of PCB real estate for just this purpose.
Okay, so before I ramble on any more... you're saying I am right in interpreting that the BTN line out will be at 12V based on the schematic, correct?
Would it not be more economical/space efficient to introduce a simple voltage divider to bring the BTN line down to 5V safe to be read by an Arduino I/O ?
I wish I had these parts laying around to somehow breadboard 
If I put a resistor ahead of the supply pin on the P channel mosfet, would it work with R2 to create a voltage divider? I'm just not sure what effect R1, the diode, and R3 would have on trying to create this voltage divider to get down to 5V
Go ahead and get a buck converter and measure the current draw with no load. Mine draws 250uA with no load, that is 1/4 of a mA. I have this type: https://www.amazon.com/eBoot-MP1584EN-Converter-Adjustable-Module/dp/B01MQGMOKI/