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Figure 1. The traditional fixed distributed power architecture is optimized for
earlier generations
of servers.
It is worth noting, however, that
peak power consumption continues
to increase to meet demands for
increased computing capability.
Typical server board consumption has
increased from a few hundred watts
to 2kW or 3kW today, and could reach
5kW or more in the future. As a result,
there is a growing difference between
the server’s minimum power at light
load and maximum full-load power.
Power distribution architectures are
becoming more flexible, with real-
time adaptive capabilities, to maintain
optimal efficiency under all operating
conditions.
Adapting the Power
Architecture
Figure 1 shows a typical distributed
power architecture comprising a front-
end AC/DC converter that delivers a
48Vdc input to an Intermediate Bus
Converter (IBC). The IBC provides a
12V intermediate bus that supplies
low-voltage DC-DC point-of-load
(POL) converters positioned close to
major power-consuming components
on the board, such as processors,
System on Chips or FPGAs. Multiple
POLs may be used to supply core,
I/O and any other voltage domains.
The 48Vdc front-end output and 12V
intermediate bus voltage have been
chosen to minimize down-conversion
losses and losses proportional to
current and distance when supplying
typical server boards. However, given
the changes in core voltage, current
draw, maximum power and difference
between full-load and no-load power,
these fixed voltages are less suited to
maintaining optimal efficiency. The
ability to set different voltages, and
change these dynamically in real-
time, allows the system to adapt
continuously to optimize efficiency.
Take Control with PMBus
The PMBus protocol provides an
industry-standard framework for
communicating with connected,
digitally-controllable power front-
end, intermediate and point-of-load
converters (figure 2). A host controller
can monitor the status of the
converters, and can send commands
to optimize input and output voltages
and manage other aspects such as
enable/disable, voltage margining,
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