Closer Look: GPU Voltage Regulator

The GPU voltage regulator is based on the ISL6569 chip from Intersil. This chip is an “intellectual”, pulse-width controller for a two-phase impulse voltage regulator. It features protection against voltage and current surges in demand, “soft activation”, balancing of currents in the channels, temperature stability of the output voltage <1% and so on and so forth. According to the specifications, it is recommended for the use with AMD Hammer processors.

Well, this is actually the first time I ever meet a two-phase voltage regulator in a gaming graphics card. They are usually seen in mainboards as regulators for powerful CPUs. Well, if the NVIDIA GeForce FX 5900 Ultra chip does consume a lot of power and requires highly stable power supply, the two-phase regulator is a must. But this is not the only discovery…

The output voltage of the regulator is set by sending a binary code to the DAC inputs of the chip:

Setting the output voltage by means of a binary code is nothing new, but the peculiarity of the ISL6569 chip is its ability to adjust the voltage “on the fly”. When the input data are changed, the controller smoothly increases or decreases the output voltage of the regulator to the new value.

It’s clear that such a “clever” regulator with a variable output voltage is not just for show. Watching the GPU voltage, I found that it really changes depending on the work mode:

• During the boot-up process, until Windows XP and the graphics card’s driver are loaded, the voltage is 1.1V;
• After the driver is loaded, the graphics core voltage becomes 1.2V. It remains the same in any 2D application;
• When a 3D application is started, the voltage goes higher, to 1.4V, and drops back to 1.2V when we return into the 2D mode.

Thus, NVIDIA engineers have endowed GeForce FX 5900 Ultra based graphics cards and the Detonator driver with the ability of controlling the GPU power supply voltage.

Why does the voltage increase in 3D? As the GPU and memory frequencies go up in 3D applications, we may suppose that the higher voltage helps the graphics card to be stable at higher clock-rates. But this doesn’t seem to be the case. It’s rather otherwise: the voltage goes down in 2D compared to 3D (as well as the frequencies do). And this is done for the card to save energy and generate less heat when it is not required to show miraculous speed.