Q: When use MAX38888, found the SuperCap can not be full charged, it is around 2.4V. Removing the charge voltage, it can not be discharged. Even charge the SuperCap to full directly, it still can not discharge. The waveform on SuperCap side is abnormal. Why & how to solve this issue.
A: According description & waveform above, it looks like the chip doesn't work properly and in oscillate status.
Review the schematic, found the output capacitor C14 is too small. We required 22uF in the datasheet, but it is 100nF (0.1uF) only in the schematic.
After replace with 22uF capacitor, the chip operation recovered.
Another issue is the resistor divider value for FBCH & FBCL is too small, it will cause the high discharge rate path for SuperCap. Suggest to keep the divider ratio but increase the resistance 10times at least. It will be better to follow the datasheet to set the bottom resistor to 499kohm.