In a world awash in SMPS ICs there needs to be something special about one
to single it out.
This one, which I haven't (yet) used looks pretty good.

    http://www.st.com/stonline/books/pdf/docs/12500.pdf

It's designed for 1.8-5.5 Vin operation but will start on 0.8V in.
Some creative power supplying would probably let it run happily below 1.2Vin
under load.

It uses an internal synchronous switch to provide claimed efficiencies over
a substantial operating range that others only dream about. Hopefully ST are
not dreaming about this one.
Many say eg 90% efficincy BUT an examination of the load curves shjows that
this is for very limited Vin and Pload. This IC is amazingly flat across a
wide range. Changing switching modes with loads helps, as does the
synchronous recitication.

eg at 5V output it claims
Over 80% at 1.2V in for 1 mA to 100 mA load.
Over 90% at 3.6Vin for from 0.7 mA to 300 mA load
Efficincie like that across such a wide range are virtually unknown.
Anyone able to prove me wrong please feel free - I'd like to make the
acquaintance of such devices.

Prices at Digikey are atrounf $US1 in 4000 volume up to about $US4+ in 1's.
Presumably available at substantially lower cost if seriously serious.

Power output is limited to 550 mA in which limits its power output at lower
voltages to useful, but more than would be nice for eg USB powering
applications.
Still an extremely useful IC



          Russell
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