I'm using a buck-boost converter RT6150B with fixed 3V3 output. I followed their application notes, and here's my circuit setup: Note: I used 22uF for C4 intead of the recommended 20uF for output capacitor. I couldn't find a good SM component for 20uF and I thought 22uF is close enough.
Testing condition: I made a small test PCB based on this schematic, and I used a external power supply to feed different input voltage levels into the IC. From Vin = 3.1V-4.2V, Vout was kept pretty stable around 3.9V (Iout~20mA), which is too high comparing to the expected 3V3 output. When I try lower Vin = 3V, Vout dropped significantly to around 1.7V (Iout~140mA).I can also hear very small buzzing sound from the IC when I was testing with it.
There are several issues here, but first of all I don't get why the output voltage is around 3.9V instead of 3.3V? I used the recommended inductor value from the datasheet for generating 3V3 at output. Other things are just capacitors to decrease the voltage ripples. I really don't know what is causing this issue.
Any help is appreciated!