At 10:45 AM 6/27/2003 -0400, you wrote:

Looking at the data sheet for the LT3400, the first thing that comes to
mind is the absolute specs for voltage on just about any pin are less than
6 volts.  So if you are producing more as you mentioned, there's some trouble.

Check your feedback network for correct values with an ohmmeter to catch
any mismarked resistors.

Boost circuits that overheat often indicate an inductor hitting saturation;
that's an area to check.

You mention changing trace sizes as well as going to a tantalum from an
electrolytic cap.  These things don't have much effect at low frequencies
usually... but I see from the data sheet that this part runs at 1MHz. How
does your pcb layout compare to the suggested layout in the data sheet? Got
short fat traces everywhere?

Check for a weak battery also.  The internal resistance goes up as the
battery gets discharged and could contribute to oscillation.

My limited experience in this area says that if there are no obvious
blunders, then the likeliest suspects are inductor saturation or feedback
circuit oscillation.

Let us know what you find.

Good luck!
Tom M.

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