Post
Topic
Board CPU/GPU Bitcoin mining hardware
Re: Is it possible to reduce MEMORY voltage for AMD GPUs?
by
DeathAndTaxes
on 27/01/2012, 14:40:38 UTC
A little more VRM pr0n.



The rectangle "big" chip at the top marked CPLA-3-50 is commonly incorrectly called the VRM.  It isn't.  It is an inductor.  The amperage used by GPU mean an external inductor is necessary.  The "A" =low acoustic noise model.  3 = 3 phase.  50=peak amperage (rated for 40).

The 3 small chips directly below the CPLA-3-50 are the VRMs.  The 5970 uses 3 phase power.  The actual GPU (the chip not the card) was designed to be powered by 4 phase power.  The 5970s are downclocked 5870s and AMD realized 3 phase is sufficient.  You will notice the board was designed for a 4th VRM.  Saves about $12 per board using 3 phase instead of 4 phase power.  Smiley

The square chip to the right (next the to red "V") is the controller for the VRM array.  It can alter the voltage between 0.6V and 2.0V (doesn't mean GPU can handle that). It also handles thermal throttling (idles card for some % of clock cycles if VRM temps get over 120C).  On 5970 each GPU subsystem is completely independent.  It is basically 2 entire cards sandwiched together and connected to a PCIe switch (big chip in dead center between the two GPUs).  Each GPU acts as if it is an independent card (w/ exception of fan control but even that is hidden from GPU).

Lastly the CP-2-50 is the inductor for non-GPU (AMD calls it "uncore") VRMs.  Yeah AMD decided to skip low acoustic noise version.  Saves about $0.20 in bulk.  Smiley  I believe this array (2 VRM, 1 controller, 1 inductor) drives the mem voltage.  Technically called VDCCI for I/O.  One possible warning.  IIRC all non-GPU voltage are handled by this "memory VRM".  A very low voltage could cause other components like PCIe switch, fan controller, monitoring ASIC, etc to fail (hopefully soft failure).  One should be careful and conservative in lowering the VDDCI voltage because it doesn't power just the memory.



Here is a shot of 5870.  You notice similar configuration except 4 phase power for those power hungry top-clocked 5870s.  You should see 1 4 phase inductor, 4 VRMs, 1 controller.