ON Semiconductor lets us know that the fake ATmega328s are actually NCP5318 buck regulators for Intel processors.
ON Semiconductor emailed us and helped us identify our mystery ICs. It turns out the semiconductor IC inside our fake ATmega328s is the ON Semi NCP5318FTR2. The NCP5318 is a Two/Three/Four-Phase Buck CPU controller. Essentially it's a voltage regulator specifically designed to power high-performance Intel processors.
This application circuit is a bit daunting. We may try to wire one up, but in general, a complex buck controller is not something that really floats our boat.
From a friend at ON Semi:
"Interesting. The AG20 is called the "Hydra lite." The hydra was originally an 8 phase Vcore buck switcher for CPU/GPU. Hydra lite was reduced to 4 phase. They were built on 18 volt bipolar process. The final version was rev 13, so it looks like that die in the picture is pre-release engineering material. Where the hell did you find that?"
Funny you should ask...
Thanks ON Semi!