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It seems like there should be a million chips for this, but for the life of me can't find any. I'm looking for a small (SOT23 or similar size if possible) IC that provides an active high when the supply voltage goes ABOVE a setpoint, and open circuit when below. Looking for ~3V trigger with up to 6V operation.

There are plenty of reset monitors that pull low when the voltage drops below the setpoint, but all the ones I've found only work down to a certain voltage, and go open circuit again when volts totally disappears. I'm using 2 different power supplies so that doesn't help me. I'm currently using the STM1061N31WX6F but discovered it doesn't work for me when there's no supply at all.

I could of course do it with several discrete components, opamps, even a microcontroller solution, but I was hoping there was a single chip solution. Google and Digikey are not being my friend today.

JRE
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Mutski
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  • Isn't that just a comparator with a voltage reference wired to the input inverting input which? That would give you HI/LO. Or a comparator with a voltage reference wired to the non-inverting input with both a pull-up resistor and PMOS base on the output? That would give you HI/Hi-Z – DKNguyen Nov 24 '21 at 04:28
  • Yes, but was hoping there was something as a small 1 chip solution. Very space constrained in my circuit. – Mutski Nov 24 '21 at 05:04
  • Can't you change your circuit to interpret things differently? – DKNguyen Nov 24 '21 at 05:10
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    All these chips are internally made with BJTs or CMOS FETs. If there is no voltage present in a circuit, there can not be a transistor that stays active and pulling low. What is your use case, maybe you don't need what you seek? Or can you use a pull-down resistor? – Justme Nov 24 '21 at 05:12
  • Perhaps you are looking for something that is not possible. – Chupacabras Nov 24 '21 at 06:09
  • Digikey search says TLV170x or MAX4008 fits your need, in a way. I'd like to agree with @Chupacabras . The solution is not here, but there with you. :) Show us your application. – jay Nov 24 '21 at 13:40
  • The TLV170x requires external voltage reference still. Max4008 is a current monitor? Was this a typo? – Mutski Nov 24 '21 at 23:30
  • Also I don't need it active with no voltage present - I can obviously use an external pulldown. I only need it active when it's ABOVE the setpoint. Thanks everyone, seems this chip doesn't exist which really surprises me. I will change the other parts my circuit to suit. – Mutski Nov 24 '21 at 23:43

2 Answers2

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Look for the TPS37xx range of voltage supervisor ICs with open-drain outputs from Ti. Choose one that is stocked somewhere...

citizen
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  • The TPS3779 with it's push-pull output is closest to what I'm after. Gives the active high when above a setpoint. External pulldown is ok for when the IC is powered off. Only downside is it requires 4 extra resistors, but that's a possibility. Thanks Citizen – Mutski Nov 24 '21 at 23:26
  • Bravo ! Resistors are cheap and small ;-) – citizen Nov 25 '21 at 08:13
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There are plenty of those. Following is MIC841LBC5TR from Micrel Inc., available at Digi-Key. enter image description here

jay
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