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Asus' Prime X299-Deluxe II motherboard reviewed

Take two

Intel's refreshed CPUs for the X299 platform gave motherboard makers a chance at a do-over in the wake of a narrowing of focus for those chips. Like I alluded to in my review of the Gigabyte X299 Designare EX, not every X299 board that's passed through the TR labs has been a winner, especially when you toss 18 overclocked Skylake Server cores in the LGA 2066 socket.

Part of that is because Intel's original vision for X299—an expandable, upgradeable platform that could host anything from four-core to 18-core chips—resulted in complex PCIe lane-routing choices and overburdened, undercooled power-delivery designs that didn't seem able to stretch across that entire range without making compromises.

In the intervening year and change, AMD's Ryzen Threadripper onslaught has made the notion of four cores on a high-end desktop platform quaint. The war is on to pack as many cores and PCIe lanes as possible into high-end motherboards, and the idea of putting mainstream desktop CPUs in high-end sockets is blessedly dead and gone. Asus has taken advantage of this opportunity to update its highest-end prosumer X299 board in the form of the Prime X299-Deluxe II.

In keeping with its Prime nameplate, the X299-Deluxe II starts out with broad swaths of white plastic shrouds, mirrored RGB LED diffusers, and brushed-aluminum accents scattered across its surface. This board has two features that immediately grab the eye, however: the real fin stack atop its primary VRM heatsink, and the sizable monochrome OLED screen mid-board that Asus calls a LiveDash.

Let's start with that VRM first. The company calls this design a "12+2" phase setup. Compared to the eight-phase design of the original Prime X299-Deluxe, more phases sounds like a welcome improvement. The story isn't quite that simple, though.

At the component level, Asus' choices for the Deluxe II look solid. The company uses a proprietary Digi+ ASP1405 PWM controller (probably a relabeled International Rectifier 35201) hooked up to 12 International Rectifier 3555 integrated PowIRstages, each capable of handling up to 60 A of output current. The thing is, if the ASP1405 is in fact a rebranded IR35201, that controller would only support up to eight native phases, as we usually saw on past Asus X299 and X399 motherboards. So how does the company get to 12 phases in its marketing materials for the Prime X299-Deluxe II?

As far as I can tell, the board doesn't actually have 12 phases. From looking at the PCB, the company has elected to double the number of power stages and inductors per phase on the Prime X299-Deluxe II without the use of PWM doublers—the components that allow motherboard makers to split out asynchronous signals from controllers that don't actually have that many native phases. While this power-delivery subsystem might look like 12 separate phases on the motherboard, it actually seems to spread the work of getting power to the CPU across fewer phases than the wizened eight-phase design employed on many of the company's past X99, X299, and X399 mobos, including the older Prime X299-Deluxe. It's difficult to understand why Asus seems to be passing off this design as a 12+2-phase system in its marketing materials.

I asked Asus about some of the reasoning behind this board's VRM design and received a wealth of commentary in return. The company notes that when designing VRMs for high-current-draw CPUs like the Core i9-9980XE, it believes the use of PWM doublers isn't ideal, as those chips add propagation delay to the PWM signal from the controller and thereby make the VRM less responsive to large transient loads—something that's no doubt worth worrying about in the case of chips with as many as 18 power-hungry, AVX-512-capable cores. The company acknowledges that creating more asynchronous phases by way of doublers improves the ripple-current characteristics of a VRM, but the company also notes that's just one parameter in a broader set of design considerations.

Source: Asus

By doubling the number of power stages per phase rather than using doubler ICs to achieve more effective phases, Asus says it has improved the amount of current each individual phase can deliver and has made a board that's better prepared for the transient loads of CPUs like the i9-9980XE. What's more, Asus says it sees an industry trend of increasing CPU current draw as the primary force behind its VRM designs, and that approach apparently didn't stop with X299 boards. The company is using this basic doubling-up-per-phase approach on some of its high-end Z390 boards, as well, and it's led to controversy among members of the extreme-overclocking community and the wider PC enthusiast world.

Source: Asus

At the end of the day, what we care about most is that a given VRM remains cool enough to allow a system to run flat-out without throttling due to the temperatures of its power-delivery circuitry. Asus says that the vast majority of the heat from the VRM is generated by switching losses in the power stages, and so long as the PWM switching frequency is the same and the number of power-delivery components used in the VRM is the same, the temperature of the system should be the same regardless of whether the number of phases is expanded by doublers or whether two power stages are used per phase.

Source: Asus

In conclusion, the company says that it is "absolutely not the case" that it omitted phase doublers from its VRM design to cut costs, as some sources have proposed.

Despite what otherwise seems like a well-reasoned response, Asus told me it isn't interested in talking about phase count on the Prime X299-Deluxe when it is, in fact, talking about phase count on its product page for the motherboard. If nothing else, buyers of $500 motherboards deserve consistency and honesty in communication. Overall, it seems to me the company would be better-served by making this "phase count isn't the only thing that matters about a VRM" argument firsthand rather than pumping up numbers for the sake of keeping up with the Joneses.

Asus has lined up a good supporting cast for its VRM, in any case. Beyond the high-surface-area heatsink, the company uses a PCB with hefty two-ounce copper layers for better heat dissipation through the circuit board itself, as well as two eight-pin EPS connectors with solid pins to help handle more current and move more heat into that PCB—not an idle concern when an overclocked X299 system can pull 600 W or thereabouts from the wall for real-world CPU loads alone.

For builders who want to test the X299-Deluxe II outside of a system, Asus includes dedicated power and reset buttons, a POST code display, a clear-CMOS button, and a dedicated button for activating the handy USB BIOS Flashback feature. USB BIOS Flashback lets a user upgrade the board's firmware with nothing more than a power supply and a thumb drive for new CPUs, and it can also be used to recover the BIOS in the event that one messes things up beyond repair—something I've had to do with the outgoing Prime X299-Deluxe a few times.

The Deluxe II also has a number of status LEDs in its top-right corner for at-a-glance troubleshooting without the decoder ring required to understand the POST code display. Hardcore overclockers or system-monitoring types won't find any voltage read points, though. Those monitoring points will likely have to wait for Asus' X299 refresh mojo to come to its ROG boards.

Since the Prime X299-Deluxe II is a standard ATX board, it's no shock to see eight memory slots supporting two DIMMs per channel from LGA 2066 CPUs. The company says that the Deluxe II has the multipliers needed to run dizzying DDR4-4266 RAM, but whether refreshed X299 CPUs are up to the task of running RAM at those speeds remains to be seen. Still, all but the most demanding overclockers should find that the Prime's memory overclocking options are up to the task.