Question Taichi z390 + 9700k: Vtt-DDR must be custom matched to the VDIMM?

[80251]

I've struggled for years to overclock my memory on this rig. I had always thought the Vtt-DDR should be set to 0.5 VDIMM. However, my Taichi z390 overvolts the VDIMM significantly (by 0.025V) and apparently doesn't have sensors to report Vtt-DDR. I had thought I needed more VDIMM even though I was already above 1.6V for 3995 @ 14-16-16-32 2T tRFC=325. I was going to give up but since there were no sensors reporting Vtt-DDR I decided to test various values of Vtt-DDR. What I needed for a BIOS set VDIMM of 1.575 (which is measured by HWiNFO64 as 1.6V) wasn't anywhere near 0.5 VDIMM though. I had to set Vtt-DDR 0.76V after testing every value from 0.7V on up. This seems to have cleared up all my instabilities. I can hardly believe it. Is Vtt-DDR THAT important or sensitive to VDIMM? Maybe the Asrock z390 Taichi overvolts the Vtt-DDR too.

 

[Lutfij]

1.6v for the ram are too high IMHO, it's either your IMC doesn't like what you're doing or your ram's IC's are badly binned. I know that the sweet spot for CoffeeLake was between DDR4-3200MHz and DDR4-3600MHz with tight latencies. Anything beyond that and you were merely generating heat or adding too much stress to the IMC...and if the kit cost you a pretty penny then you were at the point of diminishing returns.

What is the make and model of your ram kit? BIOS version for your motherboard at this moment of time?

 

[CompuTronix]

Lutfij is 100% correct.

Intel's specification for 9th Gen processor memory voltage is 1.35 +/- 5%, which is a maximum of 1.416 at the IMC (Integrated Memory Controller) on board the CPU Die. Since a precise value of 1.416 can not be selected in BIOS, any VDIMM above 1.42 is too high, which can cause instabilities and permanent degradation to the IMC. So clearly, 1.6 is WAY TOO HIGH !

See page 139, 9th Generation Intel® Core™ Processor Families Datasheet, Volume 1

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