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Figure 2. The traditional fixed distributed power architecture suited
earlier generations of servers
these converters a host controller can
optimize input and output voltages
and send commands to manage other
aspects of device operation, such as
enable/disable, voltage margining,
fault management, sequencing, ramp-
up, and tracking.
The controllability enabled by PMBus
is allowing system designers to power
architectures that are increasingly
software defined and able to respond
in real-time for optimum efficiency.
Some of today’s most powerful
techniques for optimizing efficiency
include Dynamic Bus Voltage (DBV)
optimization, Adaptive Voltage Scaling
(AVS), and multicore activation on
demand.
DBV provides a means of adjusting the
intermediate bus voltage dynamically
to suit prevailing load conditions. At
higher levels of server-power demand,
PMBus instructions can command a
higher output voltage from the IBC in
savings.
Continuously optimizing the power-
conversion architecture and bus
voltages will yield improvements in
each converter. In a power supply
comprising an IBC operating at 93%
and a POL operating at 88%, an
improvement of just 1% in each stage
can reduce the power dissipated from
18.1% of the input power to 16.3%.
This not only represents a 10%
reduction in power losses, but also
relieves the load on the data-center
cooling system thereby delivering
extra energy savings.
Software Defined Power
Requires Collaboration
While these first adaptive control
features mark the beginning of
software-defined power architectures,
many additional and even more
powerful techniques are expected
to emerge, assisted by the arrival in
the market of digitally-controllable
PMBus-compatible IBC and POL
supplies from a range of vendors.
PMBus is vital in supporting the power
supply designs that are needed to
meet the IoT challenge. However an
issue that still has to be addressed
is the “plug and play” compatibility
between supplies that appear to
offer similar specifications but behave
differently when sent the same PMBus
command.
The formation of the Architects of
Modern Power
®
(AMP) Group in
October 2014 has further strengthened
the case for digital control through its
activities in specifying standards for
the interoperability of IBC and POL
supplies. This includes standardizing
the interpretation of PMBus commands
to ensure that all supplies that comply
with AMP Group
®
standards will
operate in the same way in response
to a given command.
One of the key objectives of the AMP
order to reduce the output current and
hence minimize distribution losses.
AVS is a technique used by leading
high-performance microprocessors
to optimize supply voltage and clock
frequency to ensure processing
demands are always satisfied with the
lowest possible power consumption.
This also provides automatic
compensation for the effects of silicon
process variations and changes in
operating temperature. To support
AVS, the PMBus specification has
recently been revised to define the
AVSBus, which allows a POL converter
to respond to AVS requests from an
attached processor.
Multicore activation on demand
provides a means of activating or
powering down the individual cores
of a multicore processor in response
to load changes. Clearly, de-activating
unused cores at times of low processing
load can help to gain valuable energy
44 l New-Tech Magazine Europe