It appears that the charge current is approx 1/10 of the design value. Is it stuck in precharge mode? I know that the loop is closed because I can change the input voltage and watch the duty cycle change. It will also charge the 3s1 battery to 12.6V and turn off. The waveforms look clean, nothing is overheating, all of the voltages appear correct around the IC.
Here is the schematic.
VFB does vary as the battery charges and will eventually get to 2.1V. There is no oscillation. I checked the voltage across R504 again and it measures around 2mV across a .010 ohm. I changed to .010 ohm from the .025 ohm to match the reference design.
The loop closes because varying the input voltage changes the duty cycle. The charge current is way too low. I have about a 90% duty cyle so there should be plenty of current available through the inductor.
Simulation shows this.
