power - Design of a single cell low voltage reverse battery protection circuit

I have a design that will run off of a single cell 1.5V AA battery and I wanted to provide some reverse battery protection to it while also maximizing my run time. The classic way to do this is just with a FET.

But then I was reading a TI app note where they note that when a battery is drained to 0.8V the voltage is not sufficient to fully turn on the FET and it will operate in the linear region. Therefor the RDSon is much higher and the voltage drop will not allow the regulator (which is placed after the protection) to turn on.

Their solution in the app note is a regulator they have with a Vaux output that charges up to 2.5V before turning on the main output. This Vaux pin is used to pull up the gate of the FET thus turning it on. The part they use is a little too small for me and I was trying to figure out a way to get just this feature discretely or with some additional IC.

Has anyone run into an application like this before or have any advice?

I looked for some charge pumps but they stopped around 0.9V input where I want to get down to 0.7V (their circuit can do 0.5). I looked for some other regulators and I've considered using their regulator just for it's vaux capability :) Finally one AA battery is a hard requirement, I don't have a choice here.

Here's the TI circuit for reference:

Answer

The mosfet that you have shown is valid ,but the gate volts available is of course only the battery volts .Finding a mosfet that will give low on resistance at say 1 Volt will be hard,if not impossible. Remember that the gate source voltage must be significantly above the threshold volts .There are devices that I have not used that have a gate source threshold of 600mV .They may not give low enough on resistance for you on a single alkaline cell.There are osc circuits that could be rectified to make a realistic gate voltage .I have used a modified dynatron that starts on 700mV and can run down to 300mV on a TEG application.There are other osc circuits like joule thief and the blocking osc that I have not tried but could work .At start up the mosfet has no gate volts so the body diode could waste say 600mV .Placing a resistor across the DS of the revpol mosfet will assure low voltage start up .The resistor value is low enough to provide good starting and high enough to keep revpol prospective currents safe .