What is DrMOS—the IC Powering Next-Gen Processors?September 30, 2020 by Adrian Gibbons
Integrated powertrain devices go back at least as far as 2004 when Intel wrote the specification for DrMOS, a high-efficiency high-current IC for powering next-gen processors.
Earlier this month, Alpha and Omega Semiconductor (AOS) announced their newest generation of DrMOS power stage devices, the AOZ531xQI, aimed at high-performance PC peripherals, including graphical processors units (GPUs), memory, and laptop motherboards.
AOS claims these new DrMOS devices feature upwards of 65 A of continuous current with peak current draw being 120 A for 10 µs and 80 A for 10 ms on pulse.
Alpha and Omega Semiconductor offers integrated powertrain solutions for add-in graphics cards and gaming laptops. Image used courtesy of AOS
When Intel wrote the DrMOS 1.0 specification in 2004, it was with the intent to define an easily-adoptable component package, which filled the need for higher power densities with lower losses. Since the original revision, DrMOS has moved from a less-than-25-amp requirement to a more-than-50-amp requirement and from 64 mm2 to just 25 mm2.
So, What is DrMOS?
DrMOS, pronounced "D-R-MOS," according to Infineon Technologies, is essentially a voltage regulator module (VRM) using an external pulse-width modulation (PWM) controller in buck configuration.
The typical application circuit for a single-phase AOZ53117NQI, including the integrated driver circuitry and power FETs with external PWM controller. Image used courtesy of AOS
However, unlike traditional buck DC-DC converters, a DrMOS integrates the MOSFET drivers directly on-chip with the power FETs (PDF). As per the Intel specification, the packages for these chipsets are mostly fixed at 5 mm by 5 mm in modern implementations, allowing the VRM to be placed much closer to the load.
DrMOS offers a reduced PCB footprint, nominally 25 mm2, as well as improved power density, and reduced parasitic inductances. Image used courtesy of ASRock Super Alloy
The integration of the two power stage components, as well as proximity to the load, reduces the parasitic elements and conduction losses leading to an efficiency upwards of 95% in optimized polyphase topologies.
DrMOS devices are often found on motherboards for PCs, like the ASUS PRIME Z490-A, which claims to have a VRM topology using 12+2 DrMOS power phases (FETs, inductor, and capacitor). Multiple phases mean less current per DrMOS device, and therefore more optimization in terms of efficiency and thermal energy.
“An efficient, robust power stage plays a critical role in a graphics card performance as the heatsink on a high-performance graphics card touches both the GPU as well as the power stages," says Peter Cheng, Power IC Senior Marketing Director at AOS.
"Cooler operation results in higher peak performance of the card, and directly translates to a better gaming experience.”
Alternatives to DrMOS
DrMOS devices offer high power density in an industry-standardized form factor. But like all controller-type buck designs, they require an external PWM signal to drive the powertrain.
Analog Devices offers DC-DC controllers, like the LTC3860, which are designed to control a polyphase VRM. The package for the LTC3860 is also 5 mm by 5 mm but requires several additional passives to complete the design.
An alternative option, LTM4636, is an Analog Devices µModule in a 16 mm by 16 mm IC, which contains the complete PWM, powertrain, and inductor in one monolithic package. This µModule operates at outputs of 15 A, 30 A, and 40 A with efficiencies of 92%, 90%, and 88%, respectively.
Analog Devices says its µModule offers high-power density with fewer external components, leading to a simpler system design. Image used courtesy of Analog Devices
The LTM4636 can also operate in a polyphase topology, providing 160 W of power density at 1 V out, but with far less overall circuitry.
Design Considerations of DrMOS
As engineers, we have significant design considerations to take into account beyond power density (PDF), such as cost vs. complexity. The µModule units provide ease-of-use, both in design and bill of materials, but they also have a large upfront cost when compared to a DrMOS design.
Alpha and Omega Semiconductor DrMOS devices deliver the power density requirements for PC users who expect modern GPUs with high frame rates, ray-tracing capability, and multiple high-resolution screens.
The polyphase capability of DrMOS means longer lifespans for components by spreading current demands across multiple phases, providing more stable core voltages, and improving system thermal dissipation.
Do you have hands-on experience with DrMOS devices? If so, share your thoughts on this technology in the comments below.