How do you properly monitor supply voltages for digital circuits (microcontrollers, FPGAs, RAM)? (I stumbled upon this question when working on safety critical systems)
What I have seen a lot is to have ADCs which measure the supply voltage regularly, but these kinds of circuits perform weakly against glitches as most of the time the ADC is not measuring at the right moment. Glitches can lead to memory corruption, which can be catastrophic.
Furthermore, having a look at http://www.analog.com/media/en/technical-documentation/product-selector-card/Supervisorsfd.pdf it seems like some resilience against detecting glitches seems even desired. What makes sense, because as long as a glitch does not have a certain width or depth, it has no impact.
But I have also stumbled across some ICs (an RTC for example) which besides their normal brown-out circuitry have some edge detection to detect sudden rises or falls on the supply voltage.
To summarise, isn't it desirable to have beside the normal "static" voltage monitoring (with things like ADCs or comparators) some circuitry which can detect glitches (of a big enough width of depth to have an impact)?
Best Answer
But if there is a 'brown out' and the voltage dips below a certain value then having an ADC to monitor the situation isn't going to help.
An 'electronic fuse' is something that I've used in the past for current faults. The TPS2420 also has UVLO but it is not set-able, on some other electronic fuses they are. These type of parts have a fault pin and you can set the fault current.
If your looking to monitor the voltage for 'dips' this is a good circuit and is found in many power IC's, or you could build one with discrete components:
The schmitt trigger comparator ensures that the output doesn't flucuate and has hysteresis so if there is a dip and it's rapidly switching it doesn't switch on fast oscillations. The resistive bridge determines the voltage that the circuit detects (which should be matched with the comparator reference voltage). The current source ensures that the comparator still operates even under low voltage conditions (and you should have a capacitor on the linear supply that should keep the circuit running in bad conditions). You could run the output of this circuit into a S/R latch or the interrupt pin for a microprocessor.