Jai wrote...

>Just as a sort of update, I tried it with 20 ohms resistance... hoping to draw
>5/20 or 250mA. I couldn't even draw this much! I watched the voltage across
>the rail and dropped right to 2V, and then I shut it off immediately
>(considering what happened to my last 2). Could this really be the inductor,
>even with this little amount of current? What are typical inductors rated at
>(sorta like normal resistors are usual 1/4 watt)... it has no markings on it.
>It's pretty small, probably .5cm in diameter.

Don't confuse the load current with the inductor current; they're
not the same thing.  Even though your 20 ohm resistor is drawing
only 250 mA (at 5 volts), the instantaneous current through the
inductor is likely several times this value.

Looking at the MAX787 data sheet, I don't see any information on
inductor requirements- pretty disappointing, as Linear Technology
and National Semiconductor both normally include detailed
inductor information in their chip data sheets.  Why Maxim didn't
do this for the MAX787, I can't figure.

You need to find an inductor which will handle the peak current
without saturating, since as soon as the inductor saturates it's
current will rapidly shoot up, causing your circuit to
malfunction and probably self-destruct.

This one, from Schott,

http://www.schottcorp.com/products/pdfs/simple_switcher/67126980.pdf

is specifically intended for National's LM2577, but might work
for the MAX787.  You can poke around their website for more, and
they should be available at Digi-Key.

Dave D.

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