Traditionally, system designers
addressed increasing price
sensitivity and demands for
feature-rich products by using
ASICs, CPUs, dedicated microcontrollers,
and memory ICs for desired
product features. This hikes both the
demand for power and the complexity
of power management, forcing developers
to consider how to support
and manage multiple power-supply
sources intelligently, within the strict
power, thermal, and area constraints
of complex modern systems.
In telecommunications networking
equipment, for example, multiple
layers of hardware platform management
are implemented to control
rack-, chassis-, and board-level
network components. These layers
exist whether designers are developing
fully standards-compliant solutions,
as in the case of AdvancedTCA,
AdvancedMC, MicroTCA, or VPX
approaches; an IPMI-based semicustom
system management implementation;
or a full-custom solution
implementing intelligent power
management, regulator sequencing,
and voltage rail trimming.
In each of the above cases, designers
face basic decisions that drive the
cost, complexity, time-to-market, and
risks associated with their design.
Furthermore, the demands placed on
the system designer increase as managed
system hardware is introduced
into new high-reliability application
spaces like aerospace and military.
New market-specific capabilities,
such as unique bus structures and
encryption support, are added to the
design to meet these markets’ needs,
and any added components represent
new single points of failure for the
overall system.
Managing power is particularly
important in high-reliability applications.
At the telecommunications service
provider level, service interruptions
must be avoided. However, if
service is interrupted, data loss must
be minimized. In military and aerospace
systems, reliability concerns
are even more stringent and service
interruption and data loss can have
life or death consequences.
As military networks are deployed
in dynamically changing configurations
across a widely dispersed modern
battlefield, systems must maintain
reliability levels while coping with
extended operating temperature
ranges, severe vibration environments,
single-event-upset tolerance
mandates, and active electronic interference
from opposing forces.
Managing and controlling system
power resources entails a
number of different power-management
techniques, including
careful device selection, powersupply
sequencing, monitoring,
supervisory signal generation,
and closed-loop trimming and
margining. To implement such
a power-control subsystem,
designers typically either build a
board-level implementation with
off-the-shelf discrete powermanagement
ICs or develop a custom IC
design using an ASIC or FPGA platform.
Each of these approaches has its benefits
and drawbacks, and implementing
the best intelligent power-management
solution for a design involves consideration
of the tradeoffs.
Power-Management
Functionality
A power-management subsystem
needs to embody several key functions
to ensure proper system function and
expected performance levels: supply
sequencing, supervisory signal generation,
trimming, and margining. Supply
sequencing ensures correct startup of
a device by powering up components
in sequence according to their unique
requirements and supply voltage range.
Without such sequencing, conflicts can
arise that may impair device functionality.
Supervisory signal generation comes
into play when a sudden event interrupts
the supply of power to the system. This
technique ensures that the system will
not be damaged and that the user will be
minimally impacted by the interruption.
For example, if a user is entering data
into an application when a power interruption
takes place, supervisory signal
generation makes certain the device will
be undamaged by the sudden powerdown,
and the data and application will
remain intact upon restart.
Trimming is a control function that
keeps device components operating
within their respective supply voltage
ranges. For example, for a device
with components rated at 3.3 ±0.3 V,
performance and functionality aren’t
ensured below or above that range.
Trimming circuitry monitors power rails
and adjusts as necessary to ensure the
power reaching components is within
their specified range(s).
Margining is the most complex and
difficult of these techniques to implement.
Nonetheless, it can yield interesting
results for complex systems. A
growing number of designers needs to
dynamically alter the precise supplyvoltage
value to capitalize on potential
power savings and/or performance
improvements.
When a device operates at the high
end of its specified power range, e.g.,
3.6 V for a device rated at 3.3 ±0.3 V,
it will deliver the highest performance,
but will consume the most power. Likewise,
power consumption is minimized,
while performance is somewhat compromised,
at the low end of the power
rail voltage operating range. The ability
to selectively tweak power-supply levels
within a specified range—for example,
if our nominal 3.3-V power rail could be
dynamically adjusted within a range from
3.25 V to 3.35 V to optimize either power
consumption or performance as required
by the system at any given time—creates
a more optimized system design.
Power-supply margining addresses
this need by continuously monitoring
power rails and incrementing the rails up
or down to a user-specified value within
the device’s specified range. This action
occurs in response to signals generated
by the system requesting a move to one
optimum configuration or the other.
It’s important to note that a controller
may adjust an individual component away
from its own isolated optimized state.
When optimizing the performance versus
power consumption of an entire functional
system rack, a higher-level controller
could determine that individual
lower-level components should
operate at a less efficient configuration
to deliver the best overall
system operation.
Unlike trimming, supply
sequencing, and supervisory
signal generation, margining
is a power-control technique
that can deliver both improved
system performance and
decreased power consumption.
Closed-Loop Power-Management
Subsystem
For key power-control functions, and
in particular for power margining, a
closed-loop power-control subsystem
is essential. Only by continuously monitoring
supplies in a closed feedback
loop is it possible to make the real-time
corrections and adjustments demanded
by these techniques.
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