UVLO chip with programmable hysteresis? - Page 1
Forum section: electronics / projects

author: mlamoore
author_rank: Newbie
timestamp: August 16, 2023, 05:28:22 pm
content: 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.

author: Faranight
author_rank: Unknown
timestamp: August 16, 2023, 08:08:22 pm
content: Hello. I believe what you're looking for is called avoltage supervisorIC. I've not worked with high-voltage designs, but I've used aMIC2779to monitor voltage on a 2-cell supercapacitor. The IC would turn a boost converter on when the cap is nearly full and shut it down again once the cap is nearly depleted. Sadly, I don't think this IC will suit you since it can only work in voltages up to 5V. See, if you can find a higher-voltage IC under those keywords.

author: magic
author_rank: Super Contributor
timestamp: August 16, 2023, 08:51:32 pm
content: Maybe you could add another tap on the voltage divider and some NPN to generate a supply rail for a low voltage chip.The rail would vary from 3V to 7V over your voltage range and divider loading by base current must be considered.A second NPN could increase the output swing of an open drain output in the chip and drive the switching P-MOSFET.Admittedly not a single chip solution, but only two chips plus resistors if a dual transistor is used.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 16, 2023, 09:12:48 pm
content: Quote from: mlamoore on August 16, 2023, 05:28:22 pmA chip that handles 20V and < 20uA pushes you into rare and getting expensive part territory.Maybe a TLV6710 ? - 400mV ref and dual comparators, looks single sourced ?Addit : I see a TPS3701, but seems to be a re-badged TLV6710 ?Quote from: mlamoore on August 16, 2023, 05:28:22 pmYou can use some reset generators/voltage monitors with resistive dividers, look for ones without Icc spikes and a stable Icc at trip.You check that the divider impedance you use, to drop the sense voltages, changes by much less that hyst when the device trips.You level shift with a NPN or N mosfet, to drive your PMOS.exampleshttps://www.lcsc.com/products/Monitors-Reset-Circuits_934.html?brand=12324Some have separate Vcc and you can buy multi-rail monitors, but they tend to be much more than 2x the price of single vanilla parts, made in huge volumes.