How to use the Zippy and 850SSI on DFI nF4 - 56K caution

[EMC2]

does this mod help with vdimm stability or is it entirely a fix for the zippy psu problem?

This is pretty much only for allowing people with PCPnC 850SSI and Zippy 700W PS's to use the 5V rail for generating memory voltages without having to resort to tweaking their 3.3V rail... though it might help in other ways.

Regarding Vmem stability... as long as you have a good PS, keep the control FETs cooled properly, and stay less than 200mV below the input power rail used for Vmem generation you will have stable Vmem power during continuous operation. I've logged it with a Fluke and see less than 20mV DC deviation from no load to full load and all points in between with memory speed maxed and latency minimized.

However... if you let those FETs get too hot, it can start showing instability... and if you push closer than 200mV of the input supply rail it can as well. Here's a chart showing why you want to maintain that 200mV margin from the input supply rail on Vmem:

Charted voltages on DFI nF4 with a 3.3V rail that measured 3.31V actual


When you get to the point on the right side of the chart, the control voltage on the FETs is wide open... any spikes on the input rail will pass right through... as well as there being fluctuations in Vmem due to load changes. The same situation applies when using a tweaked 3.3V rail at higher voltages or when using the 5V rail (only with the 5V rail you're ok up to about 3.8V).

*EDIT* Here are pics showing the real thing