UVLO for Energy Harvester circuit
1a) Is this the best way to go about it?


In order to regulate Max Power Point Tracking (MPPT) for regulation depends on the source current in the range of 72% to 82% of the open circuit voltage, Voc.  This hysteretic or burp mode is analogous to the method of MPPT regulators that operate in linear mode by tracking ΔV/ΔI=Zo  load impedance becomes matched on the load line for MPPT. 

The harvesting of any current source like this one and PV's have similar MP ratios of Voc.

An LC resonant charge transfer method would be much bigger, more expensive and less stable.
So I can't think of a better way. Can you?

The Cap on HYST is for stability reasons,  like a Schmitt inverter relaxation oscillator to regulate the operating point.


  1b) Is there a simpler method that would be almost as good?


Maybe, but do want simpler? or cheaper? The math may be tricky but look at how cheap this is.


  2) How do you go about figuring out what component values you need to give the hysteresis window desired? The math seems kind of complicated and I haven't found any good guides on it.


The setpoints are a function of the bandgap Vref , and R ratios, so I would use a spreadsheet with the formula and either plot the results of  transfer functions from the formulae given or use SOLVER to iterate a variable and compute the solutions and use the criteria they give or my 72% to 82%Voc range for low to max power transfer input and then simulate with a variable weak current source to validate the results.  I have done this (Excel method) to successfully design a quasi-linear hysteretic fan speed control with thermistor resistance between 45'C and 50'C using an LM317 and an NPN on Vadj.


  3) How does the example comparator actually work? It has the HYST pin connected to a CAP into GND, normally I would have thought some sort of voltage divider would be connected to HYST?


My initial guess is internal R ratios for a fixed % hysteresis from positive feedback are reduced by negative feedback and inverted so hysteresis has a voltage control instead of R ratio control of 0.8mV/V_hyst