A Heavy-Hitting Power Supply
Beyond the heat sinks and backplate, MSI also doesn't skimp on power delivery. Its engineers used some of the best components available. Despite our extreme experimentation, we simply were not able to trigger any of this card's protection features.
Power: A Trio of Eight-Pin Auxiliary Connectors
MSI's card is powered through three eight-pin auxiliary connectors and its 16-lane PCIe slot. Most GeForce GTX 1080 Tis employ two; why does this one need three?
During normal use, even if you're overclocking, the third connector is completely useless. But when the tuning gets extreme, this card's power consumption jumps through the roof. Dynamic power is defined as P = CV2f, where V is voltage and f is frequency. So, as you might imagine, increasing V has a much bigger effect on P than f. Using certain settings, we have seen spikes beyond 1000W for just the graphics card. You can imagine that, under those conditions, the supplementary connector is a welcome addition. It also reduces the load placed on each cable. By using three connectors instead of two, the wires heat up less. And in the case of a multi-rail power supply, this offers more flexibility for distributing load.
The GPU Power Supply
Arming a card with extra connectors is only helpful if the voltage regulation circuitry can keep up. MSI equips the GeForce GTX 1080 Ti Lightning Z with seven power phases for its GP102 processor, doubled using IR3599s. International Rectifier IR3555Ms handle the conversion from 12V to lower output voltages, integrating the high- and low-side MOSFETs and Schottky diode.
Each of these ICs supports an output current of up to 60A. A quick calculation tells us that two 60A VRMs per phase times seven phases is a maximum of 840A. That's in theory, at least. These VRMs are doubled, so they'll never have to handle 60A. And even after extreme overclocking, the power supply will always incur losses due to heat dissipation and resistance. According to our estimates, we never went above the ~700A range during our most hardcore torture testing.
Again, in theory, with a supply voltage of 1.5V, we arrive at a maximum power consumption of 1260W. Knowing that the 60A rating is for continuous usage, and that the real maximum limit is much higher, we can safely proceed before applying the liquid nitrogen.
International Rectifier's IR3595A, marked with a yellow dot in the image above, controls the power hardware, enabling up to eight phases. It protects the card in multiple ways:
- OVP and UVP in case the supply voltage is too high or too low.
- OC Warn and OCP, which warns and protects if the current is too high.
- OT Warn and TP, which warns and protects if the temperature gets too high.
A signal sent by the controller arrives at the aforementioned IR3599s, which dispatch it to the two VRMs per phase. These 14 phases are, therefore, really seven doubled phases. This method is commonly used to increase the reliability of a power phase.
We've become accustomed to seeing manufacturers count all of the supply rails as independent phases for marketing purposes. But really, in this case, it's more correct to say seven phases and 14 supply rails.
The Memory Power Supply
The GDDR5X also needs power. Even though this may seem to be of secondary importance, a stable supply is critical for attaining high memory frequencies. Therefore, MSI dedicates three phases to the modules on its GeForce GTX 1080 Ti Lightning Z. This time, we're really talking about three power phases; no doubling is used.
Equipped with UBIQ QM3816N6 dual N-channel trench MOSFETs, MSI's card runs no risk of lacking current.
Similar to the GPU's power supply, the memory needs a controller. A lower phase count calls for fewer inputs and outputs, though. In the following photo, International Rectifier's 3+2-phase IR3570B PWM controller is shown with a blue dot on it.
Special BIOS and Afterburner Extreme
Boasting a power supply able to strain a nuclear reactor is all well and good, but you have to be able to fully utilize it. That's tough, since Nvidia imposes a number of limitations on its manufacturing partners. However, there's a version of Afterburner out there free of those constraints. Sadly, MSI isn't able to publish it publicly; only extreme overclockers have access to it.
With 2V available to the graphics processor and +500mV for the GDDR5X, this card's maximum frequencies shouldn't be limited by either parameter.
In our screen shot, Power Limit (%) is adjustable up to 125%. But extreme BIOSes allow you to go even further with the Power Limit completely disabled.
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