CPU Regulator Analysis
With more and more things being integrated into the CPU and PCH, there isn't much that sets motherboards apart, but the voltage regulator is still one part of the motherboard that differs greatly between motherboards. With the X99 platform, the VRM area has been effectively reduced by half, while the current demand has been almost doubled due to the high TDP of the new CPUs. The X99 VRM is possibly one of the most important parts of any X99 motherboard, especially when it comes to overclocking.
The CPU VRM features a total of 12 phases. Each phase is made up of two dual MOSFETs, and each two phases are powered by a doubler/dual driver. Half the VRM's powerhouse is on the back of the motherboard, and it is cooled by a small heat sink. ASRock is using 0.22uH 60A inductors; these are high-end ferrite inductors. Since fitting 12 phases on an X99 motherboard is very difficult due to reduced VRM real-estate, the inductors have to be small and capable, and these are both.
The inductors are actually where ASRock gets the 1300W number. We can do some quick math (power = current x voltage) to confirm. Total current will be 60A x 12 phases, which is 720A. The voltage in this case is the CPU input voltage of 1.8v. So, power = 1.8v x 720A = 1300W. This is one of the highest output VRMs for X99. There are also eight 560uF Nichicon high grade polymer can-type capacitors rated at 12K hours at 105C. That makes a total of 4480uF. So far, 12K is the highest I have seen on a motherboard for can-type capacitors.
ASRock is using an ISL6379 PWM for the CPU power, and two other ISL6379s for each memory VRM. Although this PWM has been out for a year, there is no datasheet on this PWM. According to Intersil, their other ISL637X series chips are hybrid digital PWMs: ISL6374, ISL6375, and ISL6376 are four, five, and six phase PWMs, respectively. The fact that ASRock uses two more ISL6379s for each set of memory DIMMs indicates that the ISL6379 is a dual output PWM. It should feature at least 6+2 phases, but more likely, its 7+2 or 6+3 phases, since the nine at the end of "ISL6379" would indicate the sum of all PWM outputs. This is a solid PWM with a good lineup of features. There is even one feature to allow the PWM to pulse all phases at once if needed, and you can control that through the BIOS.
ASRock is using 24 Fairchild Semiconductor FDMS3668S dual N-Channel MOSFETs. They integrate both the high-side and low-side MOSFETs into one package. These seem to be a substitute for the Texas Instruments NexFETs I usually find on ASRock's boards; however, they seem to have a slightly higher current rating. The continuous package limited current output is 30A for the high-side, and since each phase has two, you would take that 30A and double it to get 60A as max current output per phase for the MOSFETs. ASRock is using six ISL6611A phase doublers/dual drivers to double six phases from the PWM to 12 for the VRM. Intersil has worked hard on making their systems power efficient, and these doublers/dual drivers support phase shedding, and other high-efficiency technologies.
Memory Regulator Analysis
There are two sets of everything for the DDR4 power on X99; this is because there are two sets of DIMMs on every X99 motherboard. There are four DDR4 VRMs because each set of DIMMs requires a DRAM voltage of 1.2v, and a DRAM VPP voltage of 2.5v. The 1.2v rail is the most important.
Each set of DIMMs get its own ISL6379, like the CPU VRM. The DRAM voltage of 1.2v is generated by two phases of the Fairchild Semiconductor FDMS3668S, and each phase gets one of the 30A dual MOSFETs.
I couldn't find the MPDM 8632 datasheet, but there are two of them set up like integrated power stages would be. I have a feeling it might be related to the Maxim MAX8632 which is an integrated DDR controller with its own PWM which supplies both DDR and VTT voltage. Since the pins aren't sufficient to indicate that this chip is the MAX8632, we could rationalize that this is an integrated power stage with a driver for the VPP supply, which might get its PWM input from the ISL6379. The image to the right is one of four ISL6208 high efficiency Intersil drivers. Two of these drivers drive each set of the DDR voltage power phases.
DDR VPP is the voltage for the electrical high for DRAM row access. For DDR4, JEDEC decided to introduce a secondary external VRM that provides a 2.5v electrical high voltage for the word line (row access). Since the word line voltage is no longer pumped up from the DDR voltage (like it was for DDR3), the inefficiencies of pumping up the DDR voltage are gone, and instead you get power savings.
Last updated: Apr 7, 2020 at 12:33 pm CDT
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