Undervoltage detector - request for resources

Undervoltage detector

Hi,

Can any propose good article for undervoltage detector. Principally it is clear that it must consist reference lotage, resistive divider for supply and some comparator.
Can any one propose apropriate cpmparator configuration.

Undervoltage detector

If high accuracy is not required, you can employ a resistor divider + a schmitt trigger. It will have smaller quiescent current.

Re: Undervoltage detector

Ok this good information, but I need good accuarcy, and reference vltage is already designed by colleagues.

Undervoltage detector

Any kind of comparator is OK. Input voltage range should be checked according to the reference voltage you choose. An important aspect is the situation when reference is not OK.

Re: Undervoltage detector

leo_o2 said:

If high accuracy is not required, you can employ a resistor divider + a schmitt trigger. It will have smaller quiescent current.

Click to expand...

@leo_o2: A Schmitt trigger working not far (means: a few hundred mV) from its trigger level has a non-negligeable current consumption!

Undervoltage detector

To Erikl,

It depends on the structure of schmitt trigger and your design. Negligeable operating current around the threshold is possible.

Undervoltage detector

I agree with leo - any comparator will be fine. For this application I usually use a simple comparator with hysteresis (cross-coupled mirrors).

The bigger problem is that without the bandgap, this circuit will not know if the input voltage is OK or not OK. Chips using this topology often suffer an issue where they falsely report UVLO is OK when the input voltage is too low to run the bandgap.

Pushing this condition to the extreme, there is no bandgap that can run down to one Vbe, so if the comparator is not blocked during bandgap startup you will always get a glitch on the first Vbe of input voltage - hence, it's called the "diode glitch".

To avoid the issue, you need a "bandgap OK" signal that can be used to block the comparator's output until the reference voltage is ready.

Re: Undervoltage detector

I think that POR of chip will cope with this isue.