Coupled Inductors Boost Maxim’s Multi-Phase AI Chipset For Buck Design
Aiming to address applications like AI, graphics processing, and networking ASICs, Maxim Integrated is tackling the demand for scalable high-density power with a multiphase buck & coupled inductor solution.
Multiphase buck topologies for AI-powered applications are trending this past week, with new Dialog designs helping cars be smarter, not hotter.
Joining the party is Maxim Integrated with its multiphase AI power chipset, which claims to have the industry's highest efficiency and smallest total solution size with 40% less output capacitance and a 16% reduction in wasted power.
A coupled inductor can reduce the area by 1.8x over discrete. Image used courtesy of Maxim Integrated
This article will provide a datasheet and application note breakdown, explore the concept of coupled inductors, and discuss why this Maxim Integrated solution might be one for systems up to 200A.
Taking Advantage of Current Ripple Cancellation
At its core (pun intended), coupled inductors can provide higher efficiencies or smaller magnetics and output capacitance requirements. The CLH1110R1-R (a generalized model number) is used in the performance specifications for the MAX20790. The CLH1110R1-R is available in four options from 3-phases up to 6-phases.
Maxim’s proprietary coupled inductors. Image used courtesy of Maxim Integrated
Taking advantage of these multiple phases is the peak-to-peak current ripple, which is said to be reduced in coupled inductors, where Vo/Vin < 1 / Number of phases respecting the coupling coefficient of mutual inductance (Lm) to leakage (Lk).
Ripple reduction as a function of phase coupling. Image used courtesy of Maxim Integrated
Maxim's design goals for this solution are to create the highest efficiency and smallest solution size, which are partially fulfilled by taking advantage of the properties of coupled inductors.
This reduction in the current ripple means that the magnetics themselves can be smaller. More importantly, the bulk output capacitors can be reduced or eliminated due to faster transient response, thereby requiring only multilayer ceramic capacitors (MLCC).
MAX16602 Optimizes Transient Response
Overall, the MAX16602 has two critical modes of operation for maximizing efficiency and reducing the design solution size.
The first is the autonomous phase shedding (APS), which is said to maximize the regulator's efficiency by enabling or disabling phases according to two threshold crossings, APS_Fast and APS_Slow. The state control for APS allows for not only phase enabling, but also the transition into and out of continuous-conduction-mode (CCM) or discontinuous-conduction-mode (DCM).
State diagram for MAX16602 phase shedding. Screenshot used courtesy of Maxim Integrated
Secondly, the advanced modulation scheme (AMS) present in the MAX16602 claims to improve transient response, which is a key responsibility of output capacitors. The AMS enables modulation on both the leading and trailing edges. This modulation allows for phases to be turned on and off with a minimum of a delay, increasing the inductor current quickly and reducing the demand on the output capacitance.
Now that the two modes of operation are better understood let's look at an application using the MAX16602 and power-stage family.
A High-efficiency Multiphase Buck Application
One typical application for Maxim Integrated's newest AI power chipset is a subsystem, shown below, with the MAX16602 driving five MAX20778 power ICs producing a 5-phase VCORE output.
Typical multiphase buck application with a coupled inductor. Screenshot used courtesy of Maxim Integrated
The design is said to provide a peak efficiency of 95.6% at 1V8 output from the smart stage power IC family, including the MAX20778/A, MAX20779/A/B/C, MAX20780, MAX20790, and MAX16604.
Below the typical efficiency attained when utilizing the MAX20790 can be seen in a 6-phase configuration with the CLH1110-6 switching at 400 kHz. The system claims to maintain over 94% efficiency operating from 50A up to 200A at 1V8.
Efficiency peaks around 95% at 150A. Screenshot used courtesy of Maxim Integrated
All in all, this combination of hardware from Maxim Integrated’s technology portfolio is said to have three key advantages:
- Highest efficiency through lower switching frequencies
- Smallest total solution size primarily due to decreased output capacitance and phase count
- Flexibility to scale from 2 to 16 phases with a low profile coupled inductor.
Each of the three pieces of hardware partially contributes towards its goal to create the industry’s highest efficiency and smallest solution size AI power chipset.
Maxim Integrated has more than 60 US-based patents on coupled inductor design, indicating that there may be a significant benefit to incorporating this technology into your multiphase buck design.
Have you used a multiphase buck in your power designs? What were the major advantages? What were the disadvantages? Let us know in the comments below.