I've a XFX Double D Radeon HD 7950 (FX-795A-TDFC) with 2 DVI ports. Interestingly, I can only increase the voltage of the card but not decrease it. Here is the voltage table set by the manufacturer:


The default core clock of this card is 900 MHz. At that speed, no matter what I do, the voltage won't go below 1.169 V. TriXX and AfterBurner allows me to set a lower voltage (say 0.9 V), but the card will simply ignore it. GPU-Z will show 1.169 V, and the power consumption measured at the wall won't decrease.

On the other hand, overvolting does work. I can set it to 1.2+ V and reach 1100+ MHz. GPU-Z will show the voltage I set, and the power consumption measured at the wall will increase rapidly as I change the voltage.

List of things I've tried:
Use Windows 7/8 x64
Use Catalyst 13.1 and 12.3
Sapphire TriXX: force constant voltage
MSI AfterBurner: force constant voltage and extend overclocking limit
ASUS GPU Tweak: disable 2D clocks and extend overclocking limit

Any idea how I can undervolt this card?
Could it be that it's hardware locked to allow only overvolting but not undervolting?

Any help is appreciated