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ASUS Z97 Pro (Intel Z97) Motherboard - Circuit and Overclocking Guide (Page 2)

By: Steven Bassiri from Aug 11, 2014 @ 9:12 CDT

Voltage Regulator Analysis

With more and more things being integrated into the CPU and PCH, there isn't much that sets motherboards apart, however, the voltage regulator is still one part of the motherboard that differs greatly between manufacturers, and even between models of the same brand. It is important to review the hardware to see exactly what you are paying for.


The CPU VRM features a total of 12 phases with NXP LF-PAK Low RDS(ON) MOSFETs. These LF-PAKs are common MOSFETs used by a wide variety of manufacturers in lieu of traditional D-PAK MOSFETs. There are a total of 13 output capacitors, and while this number is high in regards to some other brands, ASUS is mixing the capacitance as there are only 6x560uF and 7x100uF capacitors. This gives us a total of 4060uF total capacitance, which isn't that bad considering that the LGA1150 platform CPU has its own secondary VRM to filter out any other noise.

While the Z87 Pro used 5K capacitors, ASUS decided to upgrade the Z97 Pro to 10K black metallic capacitors, just like the ROG boards - this is a nice upgrade. ASUS is employing Trio metal alloy inductors, which were first employed on ASUS ROG boards.


ASUS has used a PH4030AL as the low-side MOSFET and a PH6030AL as the high-side MOSFET, each phase gets one of each. The PWM is rebranded by ASUS, it says ASP1257, which is most likely an International Rectifier IR3580 or IR3590. It employs six phases which are then doubled to 12; this is the most common method to exceed eight phases on a motherboard. The shot of the heat sink reveals decent contact between the MOSFETs and thermal pads.


This is where things get interesting. In this image, you see 12 chips, which are drivers to drive each MOSFETs of each phase, and also three chips that double six phases to 12 phases. The blue lines indicate the doublers connected to their drivers, each doubler gets two PWM signals from the PWM controller and outputs four - you can think of it like a root system of a tree.

However, there is one extra IC, a tiny one overlooked by others, I circled it in red and also circled two drivers in red; coincidentally this little IC is connected to those two drivers as well, revealing one of those clues to how ASUS operates some of its features.


International Rectifier IR3535 a very common driver, uPI UP1911P are doublers, and the single chip discussed earlier is an International Rectifier IR3599 doubler/quadroupler. I traced back the traces leaving the PWM outputs of the IR3599 to two IR3535. ASUS has some very low power operating modes in use such as Away Mode and EPU (I measured 3W at the VRM), and I can think of only a handful of reasons to have a redundant doubler, the most likely of which has to do with branding. Certain features, such as single phase operation modes employed by companies like International Rectifier, sometimes only work when the entire system is made up of the same brand parts, in this case ASUS was able to use uPI doublers and add in a single IR doubler to use the single phase mode offered by the newer IR PWMs.

This ensures the end-user gets the best of both world's, what is more convincing of this is the position of the two drivers that are attached to the IR3599, they are in the center of the CPU power plane, providing optimal thermals.


The memory VRM is made up of two phases using the same high and low side MOSFETs used for the CPU VRM. Another PWM is being employed, this time with integrated drivers, I would guess it isn't made by International Rectifier, but it's almost impossible to tell who makes it since ASUS decided to rebrand it.


This is the VRM for the PCH. It is powered by a Richtek RT8100, the reason it doesn't say RT8100 on it is because the chip is too small to imprint that many characters, this is a common practice with tiny chips and there are guides which companies put out to identify them. It has an integrated driver which drives a single PH4030AL and a single PH6030AL, the same MOSFETs used in both the CPU and memory VRMs.

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