SEPIC buck-boost troubles

I have a LTC3441 buck-boost converter powered from a LiPo battery and want it to output 3.3V but it is outputting 4.8V instead of 3.3V. I hooked it up exactly like the "Typical Application Circuit" in the datasheet (**broken link removed**... P2149,D12796), but its still not working right. I made sure to follow the recommended pcb layout in the datasheet too.

When I put the circuit up to my ear, I can hear the inductor making weird sounds (it periodically 'clicks'). I would expect it to make a constant high frequency squeal if anything. When I press my finger against any one of the resistors on the output end (340k, 200k, 15k, 1.5nF), the output voltage will drop close to 3.3V. It does cause the chip to heat up more though, and that worries me. If it didn't heat up, I wouldn't worry about sticking a rheostat in place of the resistors to try to fix the problem. Besides, shouldn't it work as is? I am quite sure that everything is soldered correctly in place. Oh, by the way, if it helps, under normal conditions, the buck-boost converter causes the battery voltage to drop .02V, and when I touch the resistors, it drops up to .06V.

I am kind of at a spot where I am reluctant to do a lot of tweaking, for a few reasons. My analog knowledge is poor, and I really do not want to burn out the chip, because replacing it would put me back a week

Do you have any advice about how I should proceed? It seems to be a problem with the feedback section, but I am not sure how to go about fixing it. Would sticking a precision potentiometer in there be the best solution?

Thanks!


PS: Sorry about double posting, I just figured that appending my question to my year old thread was probably a little less effective.

It sounds like you might have a cold solder joint or an intermittant connection. Double check all of your component values and inspect with a high power magnifier. Resolder all the connections.

If that fails to produce results, download a copy of SwitcherCad III, and run a simulation to gain some insight on voltages and behavior that you observe. If you get really adventurous the try opening a connection to see if you can duplicate the behavior that you observe.

Brilliant! It works! It must have been either a bad connection or a bad inductor (I replaced it). Now that I think about it, I think I kept the heat on it a little too long at that would cause the windings to periodically short. Thanks again!