Eugh, that's one of the best specified "awful LDO" I've seen.
Usually, if they're bad, they just don't specify anything at all. Mystery box. Cheap Chinese things, often.
Micrel isn't a bad brand for the most part but this isn't one of their better examples.
What I'm looking for, and what it's missing:
- Is it CMOS or bipolar design (yes: bipolar)
- Supply current under different operating modes, esp. if bipolar
- Compensation, discussion of load (or source) capacitor ESR
- Graphs of operating conditions: load/line regulation, bias current, temperature variation, transient response, stability (C + ESR) ranges, etc.
This part has none of the important factors, and therefore fails my conditions. I would not design this into a new product, and I would strongly recommend designing it out of an existing product.
The reason bipolar is important is, a naive regulator will simply apply current to the PNP base as needed to maintain output (that's what the schematic says: error amp into base). When it goes into dropout, the bias current explodes as the amp tries to account for something which is no longer possible (i.e. the pass transistor is saturated, and more base current will not raise output voltage any further).
There are good bipolar LDOs, which specify that supply current (current into the ADJ/GND pin) does not increase significantly in dropout, and that remains roughly proportional to load current (being essentially the pass transistor's hFE and little more).
The disadvantage to CMOS LDOs is, the pass transistor has poor gain (near dropout, it's in the triode region where gain is low, output resistance is low, and therefore the loop characteristics change, usually to the mushy side of things), and the current density sucks (so it takes a bigger die for the same pass current and dropout voltage, often increasing cost). Poor examples still suffer from bad compensation, but in general, CMOS devices rarely suffer from anomalous current draw as the poor bipolar devices do.
Tim