[Design View / Design Solution]
Reap The Rewards Of Intelligent, Configurable Power Management
A closed-loop control subsystem, whether implemented with discrete components or a mixed-signal ASIC or FPGA, offers performance and cost advantages.
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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