5V LDO regulator @ <5V, behavior?

[ok_cool]

Can anything common be said about how LDO regulators behave when, say, 5V fixed regulator is fed with less than that? Circuit requires voltage regulation, but will tolerate if it is less than 5.

Edit answering to my own question, but it seems something can go horribly wrong:

[SeanB]

Dropout voltage will be around 200-400mV ( from the datasheet) so it will simply feed through the input less that. A big caveat though is the current drawn by the regulator through the ground pin will suddenly be a lot higher than the typical current, as it will be drawing the maximum current possible to turn on the output PNP pass device as hard as possible trying to stay in regulation. This can be an issue as it may be 100mA or more, and will often be the highest current in the circuit. If you can get a LDO that uses a MOSFET to regulate the ground pin current will not be as high when it drops out of regulation.

[ok_cool]

.. as it will be drawing the maximum current possible to turn on the output PNP pass device as hard as possible trying to stay in regulation.

So that's where it comes from. Thank you. Did not realize it would do that.

Already seemed that by picking low powered regulator I had accidentally picked one that works more sensibly and simply drops to 0: