From Micrel: MIC2876, a synchronous boost regulator with bidirectional load disconnect.
Just built up a test board (1/2" by 5/8", dominated by the input and output headers; actual circuit about 3/8" square) and verified what it does:
- When it's operating, it steps 1-cell Li-Ion voltage up to 5V (or other combinations; this pair is what I want it for), with minimal fuss and reasonable efficiency.
- When the ENABLE pin isn't being driven high, it disconnects the load from the supply.
- It operates at a decently high frequency, so the components can be small.
So, when you'd like to have a boost circuit, but you're worried about that pesky business of the input having a straight path through the inductor and rectifier to the output... this is a handy solution. Boost regulator and power switch, all in one!
Mind you, there are also applications where you'd actually want a boost regulator whose "off" output was at supply voltage; I had one of those a few years ago. The requirement at hand isn't one of those.
Update: With a 500mA load, and the particular 1.5µH, 1008 inductor I picked, efficiency is about 75%, and the little board gets rather alarmingly toasty. I've got a 1µH part of the same footprint and lower resistance that I can try, later. If I end up using this thing in the actual gadget, I may need to resort to a bulkier inductor (for which there'll be some room, on the back of the board, if I push some other stuff around). I still need to get a handle on current demand (peak, average, and how long the peaks last) for the application.