TLDR; Why does my regulator require a minimum current for stabilization if the datasheet specs 0 mA as the minimum output current?
I have a strange situation that I've "found a solution to," however I'm not exactly sure why it worked.
I'm using the STMicroelectronics ST1L05CPU33R for a design I'm working on, taking 5 V in, 3V3 out. Nothing groundbreaking. I included the 4.7 uF caps as specified in the datasheet. Schematic (you can ignore the status LED and jumper I use as a test point:
The 3V3 load is a uC and some additional logic circuitry, pulling about 180 mA. I had 10 PCBs fabricated and assembled, and noticed on 3 boards that Vout is not always the 3V3 I am looking for. From the datasheet, my understanding is there is no minimum load current for voltage regulation:
However in tinkering around, I added an 18Ω load to the output and immediately saw the voltage stabilize. Take a look at the output vs input voltages for reference:
Am I understanding the datasheet wrong, in that a minimum load current is necessary for stabilization? Its even more confusing because certain PCBs work exactly as is, some don't. To be candid, I fear my assembler in China may use some gray market parts, but don't want to point fingers until I know for sure the mistake wasn't on my end.