Well I think it's done, all you have to do is change the connectors for a better fit. I changed the diodes for lower capacitance. There are copper areas at the back for cooling, in case it overheats you can put a squishy thermal pad to the enclosure... make sure to double check everything lol

File is PCB buck boost 03

@Bob

Code for the Attiny should:

1) Check VCC is okay, then Buck=1, Boost=0

2) ADC: Monitor VOUT and VCC. When VOUT>VCC-0.5V, set Buck=1, Boost=1

3) ADC: When VOUT>desired value, set Buck=0, Boost=0

hmmm in fact due to the OR gate it's simpler:

@bobflux Woah, the PCB is looking EXTRAORDINARY!!! Thank you so so much for this. I replaced the XT60s with screw connectors. Please check the pcb, its on a new one called buck-boost convert 04. Furthermore, you mention that during phase 3, I should recharge the bootstrap cap every millisecond, but surely wouldn't I want to do this during phase 2?

Hehe thanks! During phase 2 (buck) every time the buck mosfet switches off, which is very often, the bootstrap cap is recharged, so you don't have to do anything special. But in the boost phase the buck mosfet is on continuously, it just lets current through, so the cap will not recharge, you have to "manually" nudge it.

The new connector are fine, also it's just 5A so you can use more flexible wire than the garden hose stuff that usually goes with XT60

The connector on the right may be the wrong way around, as the wires come out on the board side. But there's only ceramic caps there, so if you check the height, I mean if the top of the caps is lower than the bottom of the wire hole in the connector, then you'll be able to stick the wire in and it could be practical since it makes your board shorter, without the wires sticking out the sides...

Anyway I think you'll solder the connectors manually so you can put them facing one side or the other, but I wonder if the two "BAT" connectors (which you should label properly btw) could move a little bit to allow turning the screw terminals on the left to be rotated 180° if needed...

Also these screw terminals are pretty much square, you can also rotate them 90° so wires come out "up" or "down" instead of "left" or "right (when looking at the pcb on screen) if that's better for fitting it all together mechanically

@bobflux Placing the terminal the other way round was a mistake, It should have been facing right. Mechanically, its best if the wires face outwards. I have also renamed the "BAT" connectors to their proper names. Please can you check pcb one more time. In regards to recharging the bootstrap cap, once I set buck = 1 and boost =1, that is when I need to set each to 0 every millisecond?

OK! I swapped the pins on the connector (otherwise it wouldn't connect after being rotated)

Note when you change something you have to do: Tools->Copper area manager->Apply to make it recalculate all the copper zones, then click on the tiny "DRC" icon for design rule check, it should report "0 DRC errors" on the left panel, otherwise it shows what to fix.

what you said on bootstrap: Yes

@bobflux I am sure I rebuilt the copper plates and swapped the connectors... must have been some sort of syncing issue... Anyways, is the pcb all good now?

Looks good!