The "direct placement" approach that breaks through limitations

In conventional methods, the power supply circuit is placed next to the processor on the circuit board, and power is supplied via printed wiring. However, as the power supply route becomes longer, the effect of wiring resistance (R) becomes significant.

Conventional arrangement

In particular, under low voltage conditions of 1V or less and current conditions exceeding 1000A, power loss due to wiring resistance (I²R loss) skyrockets, leading to serious voltage drops and localized heat generation. Furthermore, the increasing density on the board poses a significant challenge, as it reduces the available space for power supply circuits.

Analog Devices' proposed "Vertical Power" solution fundamentally addresses these bottlenecks from a structural standpoint.

Vertical Power​

Vertical Power places the power module on the underside of the board—directly beneath the processor (load)—and delivers power vertically and via the shortest possible route through vias that penetrate the board. By shortening the wiring path to the millimeter, parasitic resistance and inductance are drastically reduced, minimizing power loss and voltage drop.

Source: Powering accelerator cards for AI to avoid transient effects | Analog Devices

High-density module "LTM3360B" that enables vertical power

The implementation of this Vertical Power is made possible by Analog Devices' power module, the "LTM3360B". This product is a μModule that integrates passive components such as FETs, inductors, and capacitors into an ultra-small BGA package measuring 6.55mm x 5.0mm x 3.31mm, about the size of a fingertip.

By increasing the operating frequency to 2.5MHz, we have succeeded in significantly reducing the size of the built-in inductor, and the maximum output of a single unit is 33A. This achieves an industry-leading output current density of over 1A per 1mm², far surpassing conventional products.

Its high-density design, which requires virtually no peripheral components, enables mounting in the limited space on the back of the circuit board directly beneath the processor, providing fundamental support for the power architecture of next-generation AI servers.

Compared to conventional high-density µModule products

Basic characteristics of LTM3360B

Input voltage range: 2.9V to 5.5V

Output voltage range: 0.3V to 1V

Continuous output current: 33A

• Built-in FET, inductor, Cin/Cout​

Output voltage DC accuracy: ±1%

• Remote differential output sense pin

• Internal reference voltage control using an 8-bit DAC​ ​(4mV LSB step)

• Fixed clock frequency: 5MHz (FSW: 2.5MHz)

-I²C with SMBus-compatible read/write protocol

- Analog IMON pin for monitoring output current

- Parallel connection is possible through multi-phase operation ⇒ Achievement of 1000A operation

Package: 160-lead BGA, 6.55mm*5mm*3.31mm

• Operating junction temperature range:–40°C to 105°C

Main target applications

Data Center AI Servers: Core Power Supplies for xPUs / ASICs / FPGAs

Optical modules: Optical communication modules that require compact size and high-density power supply.

Industrial and telecommunications equipment:
POL (Point of Load) distributed power systems in general

"Multi-phase architecture" is essential for AI servers.

AI processors and xPUs require exceptionally high currents exceeding 1000A to power. However, attempting to supply such high currents with a single power supply circuit (single-phase) results in extreme heat concentration (hot spots) on the power supply components, leading to reduced overall system reliability and physical limitations in implementation.

To avoid these challenges and supply high current safely and efficiently, "multiphase operation," which drives multiple power supply circuits in parallel, is essential.

Achieves a power supply of over 1000A with parallel operation of up to 12 phases.

The LTM3360B supports multi-phase parallel operation up to 12 phases. With the ability to output up to 33A​ ​per chip, parallel operation of the LTM3360B can smoothly supply the large currents of several hundred amperes to over 1000A required by the system.

Another major feature is that by distributing the small modules around the processor, the limited space on the circuit board can be utilized efficiently.

Improved reliability through heat dissipation and ripple reduction.

The true value of multiphase operation lies not simply in increasing the current value. By shifting the switching timing of each phase by a certain phase difference, the following advantages can also be obtained:

Dispersion of heat
This design avoids concentrated heat generation, which is a problem when supplying high current, and allows for balanced heat distribution and dissipation across the entire circuit board.

Reduction of output ripple voltage
By shifting the phase, the peaks and troughs of the current waveforms cancel each other out, significantly reducing the output noise (ripple component).

Reduction of external capacitors
Because ripple is suppressed, the number of large capacitors placed on the output side can be minimized, contributing to a reduction in board area and cost.

Real-time monitoring enables "uninterrupted power supply" for data centers.

In AI servers and data centers that operate 24/7, 365 days a year, sudden system shutdowns (downtime) due to power supply problems can result in extremely significant losses. Therefore, there is a strong need for "power supply visualization," which involves constantly monitoring the power status and detecting signs of abnormalities in advance.

The "LTM3360B" features an I²C/SMBus compatible 2-wire serial interface and provides advanced telemetry (remote measurement and monitoring) capabilities.

System health is managed digitally and centrally.

The built-in high-precision ADC allows for real-time collection and output of the operating status of each power module as digital data. The main parameters that can be monitored are as follows:

Real-time measurement of input/output voltage and output current.
Accurately understand the load status and power supply for each phase.

Monitoring of internal module temperature
The system detects the risk of thermal runaway in advance and provides feedback to control cooling fans and optimize the load.

Recording of alerts and failure logs
It performs prompt protective actions when abnormalities such as overcurrent, overvoltage, and overheating are detected.

Contribution to stable operation through preventive maintenance

Visualization through I²C and SMBus telemetry enables system anomaly detection and early root cause analysis, realizing preventative maintenance to avoid problems before they occur. This provides strong support for high system reliability and stable operation in high-density AI server environments.

A GUI (LTpowerPlay) is also included.

Risk of voltage spikes caused by severe load fluctuations

The xPU, which performs AI learning and inference processing, experiences drastic changes in current requirements, ranging from tens to hundreds of amperes​, at the start and end of processing. If the power supply's response to these rapid current changes is delayed, it can cause an "overshoot," where the output voltage jumps sharply, or an "undershoot," where it drops sharply.

In advanced processors with narrow voltage tolerance ranges, these voltage spikes can directly lead to malfunctions or physical damage to the IC itself, thus requiring extremely high levels of "transient response performance."

Excellent response performance due to high loop bandwidth

The LTM3360B features a control loop design that achieves high-frequency operation of 2.5MHz and a high loop bandwidth (crossover frequency of 200kHz to 300kHz). This results in excellent fast transient response performance. Even in the instant of sudden load changes, it minimizes output voltage fluctuations and maintains the strict voltage tolerance required by the processor.

It can reliably track even such rapid load fluctuations.

Optimizing board area and cost by reducing output capacitors.

Generally, to improve transient response performance, it is necessary to implement many smoothing capacitors on the output side to compensate for voltage fluctuations.

However, because the LTM3360B offers high-frequency operation at 2.5MHz and excellent response speed, the number and capacitance of required output capacitors can be minimized. This contributes significantly to saving space around the processor and reducing component costs.

Analog Devices Manufacturer Information Top

Analog Devices Manufacturer Information If you would like to return to the top page, please click below.