After having been testing the initial unit's performance for the past few days on and off, I have found a few notes to efficiency.

Using 19V input to provide 3S(12.3V)@4A output, the unit achieves extremely good ~95% efficiency of power out/power in. my bench power supply measures 51.3W output, and 12.25V@4A output.

Testing at 16V, 19V and 21V provides similar figures +-0.5% so this looks excellent for the design.

However, it appears that almost all of the 2W of heat is coming out in the QFN for some reason, which causes it to heat up rather quickly. Sometimes tripping the internal over temperature lockout.

I'm currently investigating this, and looking into easier solutions to reduce the thermal loss in the QFN.

If the thermal losses in the QFN cannot be reduced, I may need to investigate heat sinking to the outside case.