You have to size all the components first.
Calculate Lmin from equations on page 23. Calculate for both buck and boost modes and then take the bigger value to be your design Lmin.
OK - I just had a look at the gate drive - would be helpful to put in say 22 ohm as a turn on resistor on each fet - and a schottky diode ( 500mA 40V ) backward across each 22R for fast turn off - this will help immensely in reducing noise due to reverse current in diodes.
For comparison, here is the same measurement (voltage across inductor) when the dummy load is connected instead of the battery.
Vin=20.8V Iin=5.28A Vout=29.2V Iout=3.53A
View attachment 152561
I am starting to think the difference between the dummy load and battery are that the dummy load has its own current limiting and I gradually increase the load and stop before I exceed its power rating. The battery load is instant when connected and there is no current limit so it immediately overwhelms the converter and trips the overcurrent shutdown. I only can measure average charge current so I'm only seeing the average between a few cycles of the converter, then shutdown mode. Is there a reason constantly entering shutdown mode would cause the inductor to get very hot?
It should be 20. 0.2% as ripple would of course be too tight.
You probably need more patience. Take a little time out. A little more thoughtful view might just be all you need. I'd say you should abolish completely the idea of emulating the other board. Concentrate more on the datasheet information.
One thing you haven't done is providing your schematic as is.
Now you need to design a current regulation loop that does that for you....
I believe you are 100% correct. I have been using a scope probe with ground wire clip but trying to measure current sense over 3mR, the induced noise in the ground wire and probe tip are more than the true signal - so it makes me think there is 200A spikes. I recently learned about these ground tips to use that reduce the loop area of the probe and reference-Usually these problems are linked to RFI noise getting into the current sense pins - hard to see with a scope because putting the scope probe on the pin introduces MORE noise - use a leaded 10k ( or 4k7) resistor attached to the end of the probe with 4mm of wire from the R body to probe the I sense pins - you may be able to see something
Yes.... that is why I went searching for the ground probe tip, that's exactly what was happening. Everytime I connected the ground clip, the current would change.if you probe directly and it gets worse ( less charging current ) you know RFI is the problem ...
It may pay to put a flux band around the choke and hook it to 0v via a 4R7 - this will limit magnetic RFI from getting into your control chip ( and the tracks from I sense R to the chip )
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