I have a somewhat strange behavior on a TPS61029 design. I've used the TPS61026 previously and do not see this behavior with that circuit board. Basically what happens is that as I reduce the resistance of the load on the regulator output, the current goes up to a point and then the voltage drops dramatically.
I originally had the voltage feedback set for an output of 5V. I added a potentiometer to the output and decreased its resistance while monitoring the load current and output voltage. Around 25 mA, the output voltage dropped almost immediately to 2.8 V. I looked at the switch output on pin 9 and it went from a square wave at 25 mA to a heavily distorted waveform beyond that point.
I originally had the 5V regulator output routed to one plane of my two layer board, but I cut this plane free and suddenly I was able to increase the load current to 100 mA before the output voltage would drop. I'm not sure if my power plane was capacitively coupled to the parallel ground plane, or why cutting the power plane loose would cause this change.
So I don't really understand why I am seeing this behavior. More importantly, I'd like to get more like 250 mA out of this design. It should be able to do that as far as I can tell, but I am not close yet. Any ideas? I know switchers can be finicky, but I'm not quite sure what the issue could be here. I assume there's some stray capacitance somewhere but I don't know quite where to look. I have attached a schematic and a snippet of
my layout for reference.
