1.65 V is the max recommended voltage to RAM when Vqpi is on default.
The technical reason is that memory controller is powered at Vqpi and it is physically connected to RAM.
To avoid that Vram comes back to IMC, destroying it, there are protection diodes that block the Vram voltage.
If the difference between Vqpi and Vram is less than 0.47 V, the diodes are closed but over 0.47 V the junction opens and Vram can go to IMC, destroying it.
If you want to use Vram over 1.65 V, the trick is to push Vqpi to mantain Vram>Vqpi difference less than 0.47 V.




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