I tried the circuit with LTC3225 and LTC4412 from the Application ("Supercapacitors Can Replace a Backup Battery for Power Ride-Through Applications − Design Note 450").
My Goal is to have 4.5V or more for approx. 1s, the current I need is about 330-450mA. For the moment I don't use a DC/DC converter at the output.
So the first issue I had was, that the LTC3225 didn't seem to charge (PGOOD stays low), when setting RPROG=4k7 (according to datasheet RPROG must be >2k).
So I set RPROG = 12k.
This is what my schematic looks like (the orange highlighted parts are slightly different from the application note):
I use the P-MOSFETS NTLUD3A50:
Unfortunately the Voltage drops way to fast.
Also when I measured the signals it seems as if the FET's are not switched digitally (with opposite levels) but rather are in a kind of amplifier mode.
For a short time the PGOOD oscillates when only one FET is fully conductive.
Zoom of previous oscillation:
Can you give me any advice to improve my schematic.
Or is there any mistake I am missing?