Ooops, my mistake. You are right, I did not understand the difference between IO voltage and VDD voltage.
I should have been more careful, I was wrong, sorry :-(
In case anyone is interested in making the hardware support 1.35V (which I won't do), here is the specsheet for the voltage regulator. It has equation 6 explaining how to chose R2 to get the wanted voltage.
http://www.ti.com/lit/ds/symlink/tps51916.pdf
Supporting 1.35V should just be a matter of swapping R2, which can still be hard with SMD. Maybe when the motherboards are cheap enough?
On Sat, Nov 12, 2016 at 6:46 PM, Nico Huber nico.h@gmx.de wrote:
On 12.11.2016 05:00, Charlotte Plusplus wrote:
Hello
On Fri, Nov 11, 2016 at 5:37 PM, Nico Huber nico.h@gmx.de wrote:
The W520 does only have 1.5V DDR voltage. If it's stable with vendor bios, it's not a DDR voltage problem at all.
Based on my reading of the block diagram and crossing that with a cpu pinout and the cpu specs, I disagree. The W520 indeed only support 1.5V, if you mean 1.5V vs 1.3 "low voltage" DDR3L.
But SA_DIMM_VREFDQ is in direct control of the DDR3 voltage: "The step
size
is 7.7 mV". So it supports 1.5V +- k*0.007V, with k being given by the
XMP
profile.
In case this is not clear, on http://www.intel.com/content/dam/www/public/us/en/
documents/datasheets/3rd-gen-core-family-mobile-vol-1-datasheet.pdf
: Page 30 : "The processor memory controller has the capability of
generating
the DDR3 Reference Voltage (VREF) internally for both read (RDVREF) and write (VREFDQ) operations. The generated VREF can be changed in small steps, and an optimum VREF value is determined for both during a cold
boot
through advanced DDR3 training procedures in order to provide the best voltage and signal margins."
That seems to be a lot of evidence in the voltage not being an absolutely fixed 1.500V. It is something more flexible!!!
You're confusing the memory's operating voltage (what XMP and DDR3 vs. DDR3L is about) with i/o voltages. VrefCA is the reference for Command/ Address lines and VrefDQ is the reference for Data lines from what I understand.
For the operating voltage have a look at page 86 in the Kendo-3 schema- tics. The TPS51916 provides the voltage VCC1R5A which is VDD for the DIMMs. You can see from its datasheet that it's controlled by REFIN which is generated by dividing VTTREF (1.8V) by the resistors R1056 (10K) and R843 (48K7). If those resistors were configurable in any way, you could control the operating voltage. But they are just plain resistors.
So even if the processor had dedicated pins to control the voltage, they are not used in this machine.
Nico