5V Step-Up/Step-Down stuck at 3.9VDC output

I’d like to use the 5V Step-Up/Step-Down regulator (item 2870, S9V11F5S6CMA) to provide 5V input to a raspberry pi zero w from a 3.7V Li-ion battery pack. It needs to be a boost+buck converter because the battery pack is being charged from a 6V solar panel connected to a charge controller that will either give juice straight from the panel in sunlight (nearly 7V) or from the battery if at night.

The problem is that the boost+buck converter seems to regulate to only 3.9V, no matter what input voltage I apply. To test it, I adjusted the input voltage from 3V to 12V, and the output voltage is always 3.9V. I haven’t done anything with the adjustable low-voltage cutoff. Any advice?



Since you are getting something out, it is probably not an issue with the low-voltage cutoff. Was there anything connected to the regulator output during your testing? Could you post pictures of your setup that show all connections including the solder joints? Could you try it with only the battery attached?