I'm new here, so forgive me if I breach any forum protocols in the asking of this question.
I have designed a voltage regulator scheme for a guidance system on an aerial drone. All components require either ~4V (they have an input range) or 3.3 V exactly. My solution is pictured here in a schematic and a board layout. I used the TPS53318 switcher to regulate my battery voltage down to 4 volts with roughly 3 mVpp noise, then used an LP38502 LDO to convert that into nice clean 3.3 V with as little wasted power as possible. Datasheets here: TI TPS53318 and TI LP38503.
So, my problem: It doesn't work. The output from the switching regulator is a very small oscillating negative voltage, which I assume is caused by some sort of LC oscillation in the absence of any real output.
- I've isolated the LDO, and it does it's job fine when supplied with 4V from an external supply.
- I have tried reflowing my solder, even replacing the switcher itself (I always order 3 times as many as I think I'll need) and I still see the same problem.
- I've done my best digging around with a multimeter and a scope trying to find a resistor with the wrong value or something, but I'm coming up empty handed.
This is my first time trying to troubleshoot this type of circuit, or any electronics this small on a proper board, so I'm hoping that someone here might point out errors I might have made or possible bugs I can attempt to diagnose. The oscillating negative voltage output still seems odd to me, and I'm not entirely satisfied with my idea that it is caused by LC dynamics, so I'm also hoping that someone might be able to suggest a possible cause/solution for that effect.