AMD Polaris (RX 470/480/570/580) Memory Voltage
AMD Polaris cards (including the RX 470, 480, 570, and 580 are said to have a fixed memory voltage (MVDD), and it is impossible for software to change this. This, however, is not true. First, I will cite a post which describes the power delivery of these cards fairly well, and asks about software modification of the voltage. Second, I will detail how it is possible to adjust the voltage from software.
The aforementioned post is here. The specific (translated) part I wish to reference is:
Can someone confirm to me that it is not possible to modify the memory voltage (in a software way) on a reference card? According to the layout, this is not possible because the PWM 6 + 2, the +2 secondary phases are not used (the memory is controlled via a GS7256 from GStek: http://www.gstekic.com/pdf/GS7256 .pdf => no i2c interface).
He is correct that the GSTek GS7256 is not software programmable. Let's have a look at it on the reference schematics:
But, if you follow its FB input (feedback), you'll find that there's an I2C programmable rheostat connected to it!
Utilizing the AD5272/AD5274 digital rheostat to modify the FB (feedback) resistance, one can make the GS7256 change its output voltage. A higher resistance will raise the output voltage, a lower resistance will lower the output voltage. This is used by AMD to support different GDDR5 modules with different voltage needs.
This should be the final bit needed to figure out what resistance values are needed.