VDDC / Voltage Fluctuations - Overclock.net

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post #1 of 2 Old 03-13-2013, 01:55 AM - Thread Starter
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I'm looking for some insight as to why my VDDC voltage is not constant under load.

I have a couple of Gigabyte 7950WF3's that I picked up yesterday.

Currently running 1150/1500 (Crossfire) at 1.2v as a test, no issues with artifacts or anything, however there is major fluctuation in VDDC Voltage.

This occurs only under load, even if I set Constant Voltage in MSI Afterburner, it still fluctuates under load.

Average fluctuations (Under Load)

1.2v in MSI AB - 1.13 - 1.170 VDDC
1.25v in MSI AB - 1.15 - 1.198 VDDC
1.3v in MSI AB - 1.15 - 1.21 VDDC

Actual VDDC when Constant Voltage is set (IDLE)

1.2v MSI AB - 1.193 VDDC

I can't work out why the huge fluctuations, it may be preventing me from OCing beyond 1200 on the core. (Temps are extremely good with these WF3's).

Here is a quick log from GPU-Z during the first GPU test on 3D Mark 11, It shows the VDDC fluctuations.
Code:
        Date        , GPU Core Clock [MHz] , GPU Memory Clock [MHz] , GPU Temperature [°C] , GPU Load [%] , VDDC [V] , MVDDC [V] , VDDC Current [A] , VDDC Current In [A] , VRM Temperature 1 [°C] , VRM Temperature 2 [°C] ,

2013-03-13 20:42:03 ,              300.0   ,                150.0   ,               41.0   ,          0   ,  0.805   ,   1.500   ,            2.8   ,               0.2   ,                   43   ,                   45   ,

2013-03-13 20:42:04 ,              300.0   ,                150.0   ,               41.0   ,          0   ,  0.805   ,   1.500   ,            2.5   ,               0.2   ,                   43   ,                   45   ,

2013-03-13 20:42:05 ,              300.0   ,                150.0   ,               41.0   ,          0   ,  0.805   ,   1.500   ,            2.3   ,               0.2   ,                   43   ,                   45   ,

2013-03-13 20:42:06 ,              300.0   ,                150.0   ,               41.0   ,          0   ,  0.805   ,   1.500   ,            2.5   ,               0.2   ,                   43   ,                   45   ,

2013-03-13 20:42:07 ,              300.0   ,                150.0   ,               41.0   ,          0   ,  0.805   ,   1.500   ,            2.5   ,               0.2   ,                   42   ,                   45   ,

2013-03-13 20:42:08 ,              300.0   ,                150.0   ,               41.0   ,          0   ,  0.805   ,   1.500   ,            2.0   ,               0.1   ,                   42   ,                   45   ,

2013-03-13 20:42:09 ,              300.0   ,                150.0   ,               41.0   ,          0   ,  0.805   ,   1.500   ,            2.5   ,               0.2   ,                   42   ,                   45   ,

2013-03-13 20:42:10 ,              300.0   ,                150.0   ,               41.0   ,          0   ,  0.805   ,   1.500   ,            2.3   ,               0.2   ,                   42   ,                   45   ,

2013-03-13 20:42:11 ,             1150.0   ,               1500.0   ,               45.0   ,         64   ,  1.189   ,   1.500   ,           18.3   ,               2.0   ,                   42   ,                   45   ,

2013-03-13 20:42:12 ,             1150.0   ,               1500.0   ,               45.0   ,         64   ,  1.188   ,   1.500   ,           18.5   ,               2.0   ,                   43   ,                   45   ,

2013-03-13 20:42:13 ,             1150.0   ,               1500.0   ,               46.0   ,         64   ,  1.189   ,   1.500   ,           18.5   ,               2.0   ,                   43   ,                   45   ,

2013-03-13 20:42:15 ,              300.0   ,                150.0   ,               42.0   ,          0   ,  0.848   ,   1.500   ,            3.0   ,               0.2   ,                   44   ,                   45   ,

2013-03-13 20:42:16 ,              300.0   ,                150.0   ,               42.0   ,          0   ,  0.805   ,   1.500   ,            2.8   ,               0.2   ,                   43   ,                   45   ,

2013-03-13 20:42:17 ,              300.0   ,                150.0   ,               42.0   ,         86   ,  0.947   ,   1.500   ,            4.8   ,               0.4   ,                   43   ,                   45   ,

2013-03-13 20:42:18 ,              300.0   ,                150.0   ,               42.0   ,          0   ,  0.805   ,   1.500   ,            2.0   ,               0.1   ,                   43   ,                   45   ,

2013-03-13 20:42:19 ,              300.0   ,                150.0   ,               41.0   ,          0   ,  0.805   ,   1.500   ,            2.5   ,               0.2   ,                   43   ,                   45   ,

2013-03-13 20:42:20 ,             1150.0   ,               1500.0   ,               47.0   ,         64   ,  1.141   ,   1.500   ,           93.8   ,               9.8   ,                   43   ,                   45   ,

2013-03-13 20:42:21 ,             1150.0   ,               1500.0   ,               52.0   ,         64   ,  1.148   ,   1.500   ,           94.3   ,              10.5   ,                   44   ,                   46   ,

2013-03-13 20:42:22 ,             1150.0   ,               1500.0   ,               53.0   ,         64   ,  1.148   ,   1.500   ,           93.5   ,              10.6   ,                   45   ,                   46   ,

2013-03-13 20:42:23 ,             1150.0   ,               1500.0   ,               54.0   ,         64   ,  1.152   ,   1.500   ,           87.5   ,              10.5   ,                   46   ,                   47   ,

2013-03-13 20:42:24 ,             1150.0   ,               1500.0   ,               54.0   ,         64   ,  1.150   ,   1.500   ,           93.3   ,              11.4   ,                   47   ,                   48   ,

2013-03-13 20:42:25 ,             1150.0   ,               1500.0   ,               55.0   ,         80   ,  1.137   ,   1.500   ,           87.0   ,               9.4   ,                   47   ,                   48   ,

2013-03-13 20:42:26 ,             1150.0   ,               1500.0   ,               55.0   ,         89   ,  1.148   ,   1.500   ,           88.3   ,              10.7   ,                   48   ,                   49   ,

2013-03-13 20:42:27 ,             1150.0   ,               1500.0   ,               56.0   ,         89   ,  1.156   ,   1.500   ,           94.5   ,              10.8   ,                   49   ,                   49   ,

2013-03-13 20:42:28 ,             1150.0   ,               1500.0   ,               56.0   ,         89   ,  1.135   ,   1.500   ,           96.3   ,              11.4   ,                   49   ,                   49   ,

2013-03-13 20:42:29 ,             1150.0   ,               1500.0   ,               57.0   ,         89   ,  1.139   ,   1.500   ,           69.0   ,               9.0   ,                   50   ,                   50   ,

2013-03-13 20:42:30 ,             1150.0   ,               1500.0   ,               57.0   ,         89   ,  1.139   ,   1.500   ,           85.3   ,              10.1   ,                   50   ,                   50   ,

2013-03-13 20:42:31 ,             1150.0   ,               1500.0   ,               58.0   ,         89   ,  1.143   ,   1.500   ,           97.5   ,              11.6   ,                   51   ,                   51   ,

2013-03-13 20:42:32 ,             1150.0   ,               1500.0   ,               58.0   ,         89   ,  1.146   ,   1.500   ,          100.8   ,              11.0   ,                   51   ,                   51   ,

2013-03-13 20:42:33 ,             1150.0   ,               1500.0   ,               58.0   ,         89   ,  1.139   ,   1.500   ,           98.8   ,              12.0   ,                   52   ,                   52   ,

2013-03-13 20:42:34 ,             1150.0   ,               1500.0   ,               59.0   ,         90   ,  1.170   ,   1.500   ,           79.8   ,              10.6   ,                   52   ,                   52   ,

2013-03-13 20:42:35 ,             1150.0   ,               1500.0   ,               59.0   ,         90   ,  1.160   ,   1.500   ,           86.0   ,              11.0   ,                   53   ,                   52   ,

2013-03-13 20:42:36 ,             1150.0   ,               1500.0   ,               59.0   ,         90   ,  1.145   ,   1.500   ,           96.0   ,              11.8   ,                   53   ,                   53   ,

2013-03-13 20:42:37 ,             1150.0   ,               1500.0   ,               60.0   ,         91   ,  1.143   ,   1.500   ,          104.0   ,              12.3   ,                   54   ,                   53   ,

2013-03-13 20:42:38 ,             1150.0   ,               1500.0   ,               60.0   ,         91   ,  1.131   ,   1.500   ,          100.0   ,              12.0   ,                   54   ,                   53   ,

2013-03-13 20:42:39 ,             1150.0   ,               1500.0   ,               61.0   ,         91   ,  1.162   ,   1.500   ,           93.8   ,              11.3   ,                   54   ,                   54   ,

2013-03-13 20:42:40 ,             1150.0   ,               1500.0   ,               61.0   ,         91   ,  1.137   ,   1.500   ,          106.0   ,              12.8   ,                   55   ,                   54   ,

2013-03-13 20:42:41 ,             1150.0   ,               1500.0   ,               62.0   ,         91   ,  1.135   ,   1.500   ,          106.0   ,              12.9   ,                   55   ,                   54   ,

2013-03-13 20:42:42 ,             1150.0   ,               1500.0   ,               62.0   ,         91   ,  1.143   ,   1.500   ,           91.0   ,              14.8   ,                   56   ,                   54   ,

2013-03-13 20:42:43 ,             1150.0   ,               1500.0   ,               62.0   ,         91   ,  1.139   ,   1.500   ,           86.8   ,               6.6   ,                   56   ,                   55   ,

2013-03-13 20:42:44 ,             1150.0   ,               1500.0   ,               62.0   ,         91   ,  1.164   ,   1.500   ,           93.3   ,              12.6   ,                   56   ,                   55   ,

2013-03-13 20:42:45 ,             1150.0   ,               1500.0   ,               62.0   ,         91   ,  1.160   ,   1.500   ,           94.5   ,              11.5   ,                   57   ,                   55   ,

2013-03-13 20:42:46 ,             1150.0   ,               1500.0   ,               63.0   ,         91   ,  1.145   ,   1.500   ,           98.8   ,              12.3   ,                   57   ,                   56   ,

2013-03-13 20:42:47 ,             1150.0   ,               1500.0   ,               63.0   ,         91   ,  1.152   ,   1.500   ,           94.8   ,              11.8   ,                   57   ,                   56   ,

2013-03-13 20:42:48 ,             1150.0   ,               1500.0   ,               63.0   ,         91   ,  1.145   ,   1.500   ,           96.3   ,              10.9   ,                   57   ,                   56   ,

2013-03-13 20:42:49 ,             1150.0   ,               1500.0   ,               63.0   ,         91   ,  1.152   ,   1.500   ,           85.8   ,              10.7   ,                   58   ,                   56   ,

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post #2 of 2 Old 03-13-2013, 05:29 AM
 
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This is Vdroop and this is normal.

The voltage droops more, the more current flows through the supply stage. This is why you see almost the exact voltage set when idle (low load).
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