Why does this LDO regulator have a 15V output limit?

[merlinb]

I was looking at a MIC29312 low dropout regulator and noticed something odd. The datasheet says the maximum input voltage is 20V, but it goes on to say "the adjustable regulator version, MIC29312, allows programming the output voltage anywhere between 1.25V and the 15V maximum operating rating of the family." 

Why would the limit be 15V? Surely the output can be set anywhere up to 20V minus the drop-out voltage, like with any other regulator? (Ignoring more elaborate voltage boosting techniques).

http://www.micrel.com/_PDF/mic29310.pdf

[TejfolvonDanone]

The +20V supply is in the ABSOLUTE MAXIMUM ratings and not in the OPERATING RATINGs. In the datasheet there is note 1 for absolute maximum and note 2 for operating ratings:
Note 1.
Exceeding the absolute maximum rating may damage the device.
Note 2.
The device is not guaranteed to function outside its operating rating.

[R.G.]

Correct. It's the technical version of "just because you can do something, that doesn't mean you should do it."

[PRR]

> says the maximum input voltage is 20V

Actually -20 to +20.

So I can put in -10V and set the output to -8V?

There is a semi-schematic on page 4. If the input goes to +16.6V, the output is turned off. I don't think you can expect happiness with much over 15V supply.

[PRR]

"For applications requiring even lower dropout voltage, input voltage greater than 16V, or an error flag, see the MIC29300/29301/29302/29303."

These are said to work at +26V input (-20V to +60V in shut-down).

[merlinb]

There is a semi-schematic on page 4. If the input goes to +16.6V, the output is turned off. I don't think you can expect happiness with much over 15V supply.

Hmm, yes I suppose that must be it. It will survive 20V intact, but will not function normally above ~16V.

[PRR]

> said to work at +26V input (-20V to +60V in shut-down).

This implies some "Reverse Polarity Protection" action, as long as you know it won't be more than 20V reverse. Self-defense against idiot or distracted users.

It would also take any junk 6V to 26V (10V to 26V) and give steady 5V (9V) output.

And reject up to 60V the right way; though I think if you have over 24V on a stage then bad things will find a way to happen.