I'm looking for a chip that will monitor its supply voltage and act as a UVLO to turn on a P-channel MOSFET (or internal 30mA+ switch) once the supply voltage rises above a resistor-programmable threshold (18V for me) then keep it on until it falls below a lower resistor-programmed threshold (10.5V for me). The chip needs to handle up to 20V absolute max and needs to draw low supply current (I'd say 25uA or lower).
To avoid the X-Y problem, I've got a working power supply prototype that runs on 480VAC. Because of various factors, I'm using a control chip that was intended for use with a PFC pre-regulator (that I don't have) so it assumes you already have a bias supply and doesn't have this sort of high-hysteresis UVLO built-in like other power supply controllers I've used in the past. My overall control circuit draws up to 20mA (looking at all the datasheet worst-case values), while my startup HV current source provides less than 1mA. I need to keep the control circuits powered off while a capacitor charges to around 18V (the control circuit can handle 20V absolute max), then turn on the control circuit and keep it on as the supply voltage falls before the aux winding starts providing power. In case there's some sort of problem, I want to turn off the control circuits if the voltage falls below 10.5V or so to let the caps recharge and try again.
I currently have a circuit working (after several tweaks) that uses a voltage reference, comparator, P-channel FET, and a dozen or so passives. I'm wondering if there's a simpler (and smaller) way to do this, though. This sort of functionality is built into many low-cost power supply controller ICs; it seems like there should be a stand-alone equivalent (with built-in provisions for hysteresis or an appropriate polarity output signal to let me add a positive feedback resistor), but almost every chip I looked at is only intended for 7V or lower, can't provide the hysteresis I need, or otherwise won't work. It's really hard to search for, though, because there's so many options that won't work and no good way to filter them out.