"Power supplies" is perhaps not the correct sub-forum, but all the right people are here so I post here... 
I have a fault signal, at the moment 3.3 V logic but this is negotiable, which I wish to store. A simple OR-gate will solve this, but only until the supply voltage is cycled. An MCU would be a simple solution but here is the real issue, I don't even have 1 mA to spare, at least not continuously. Any voltage level yes, but current no. All glue around this lives on a few uA.
It can be OTP.
It does not have to be fast. The fault condition signal will be present for several seconds before the power can be cycled.
Any suggestions?
I have a fault signal, at the moment 3.3 V logic but this is negotiable, which I wish to store. A simple OR-gate will solve this, but only until the supply voltage is cycled. An MCU would be a simple solution but here is the real issue, I don't even have 1 mA to spare, at least not continuously. Any voltage level yes, but current no. All glue around this lives on a few uA.
It can be OTP.
It does not have to be fast. The fault condition signal will be present for several seconds before the power can be cycled.
Any suggestions?
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Diode couple the supply to the OR gate and supply the gate from a backup cap or backup battery when in standby.
Sorry, not allowed to use batteries due to risk of leaks. 🙁
Any solid-state solution? Ultra-low-power OTP memory?
Any solid-state solution? Ultra-low-power OTP memory?
How long is the event to be hold without power ?
How much current is needed by the circuit that receive the event signal ?
And how to reset it ?
Mona
How much current is needed by the circuit that receive the event signal ?
And how to reset it ?
Mona
Use a purpose designed backup cap. Very very small and would power it for months. Remember the gate uses zero power (apart from internal leakage) and even a 1uf film cap would power it for far longer than you might think.
Preferably indefinitely. If someone takes it out of service and installs it five years later, it may be/is still damaged.
Less than 10 uA. I can store some energy into a capacitor if the OTP/circuit which stores the flag/fault-bit takes more current than that for a short amount of time. Problem is Iq or just the current consumption when active but not writing the flag/fault-bit.
Send it in for service / electronic waste bin.
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Or if I turn the question around, how much current does the smallest and lowest powered MCU with built in non-volatile memory consume these days?
Something like a PIC costs peanuts but its complex solution to the single gate you showed earlier.
Back to this issue. An ATtiny should be able to do the job with <uA consumption after some research. This guy measured an ATmega with some tweeks to only respond to a hardware interupt as low as 0.15 uA, which is fine in my application. Gammon Forum : Electronics : Microprocessors : Power saving techniques for microprocessors
Have to check if it boots fast enough and can blip a 1 into the OR-gate to latch it before I run out of stored energy in the capacitor, and then put it back to sleep.
While at it, I'm thinking of other saftey scemes. A second overtemperature protection comes to mind if the main system breakes down compleatly. Does it exist such a temperature sensor that can be biased with just uA?
Have to check if it boots fast enough and can blip a 1 into the OR-gate to latch it before I run out of stored energy in the capacitor, and then put it back to sleep.
While at it, I'm thinking of other saftey scemes. A second overtemperature protection comes to mind if the main system breakes down compleatly. Does it exist such a temperature sensor that can be biased with just uA?
One Time Programmable solutions include: fuses! Blow a fuse, it will remember it was blown no matter how many times you cycle the power after that. (Here are 78 of them) that you can write with a 2N3904 and read with a CMOS gate's input pin.
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