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Posted on 27 May 2019

Advanced Regulator Modules Bring Flexibility to High-Density Power Subsystems

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The long-standing trend of increasing efficiency in power-conversion, from the upper 80s of percent to the mid and upper 90s, has come thanks to innovations spanning power-switching device designs, converter-control techniques, and component-packaging technologies. Beyond the obvious operational cost benefits that high-efficiency power subsystems bring to the products they inhabit, one consequence of this trend has been a significant increase in achievable power densities.

By Ian Mazsa, Manager, VI Chip Product Line, Vicor

Converters capable of delivering several hundred watts have commonly occupied brick packages that cover as much as 65 cm2 of board space and consume 83 cm3 of package volume. These have been joined by converters of comparable power capability available now that occupy barely over 7 cm2 of board space and deliver roughly 100 W/cm3.

The effect of such small board areas and high power densities extends well beyond the power subsystem. Reducing the power subsystem size and weight can bring numerous follow-on effects beneficial to the overall system design. Indeed, in highly space-constrained applications, such as on-board systems for aircraft, such high power densities facilitate electronic functions that would otherwise not fit in the already confined room available for instrumentation. The same high power density converters are also relieving space constraints while satisfying power demands in computing, communications, and industrial process control applications, among others.

More recently, configurable versions of these high power density converter modules have become available. These flexible modules allow you to optimize their parametric performance to your application’s requirements while at the same time reducing external circuitry.

For example, Vicor’s VI Chip® PRM™ nonisolated regulator modules are available in full-sized packages measuring 32.5 x 22 x 6.73 mm and can deliver up to 500 W of power (figure 1). The buck-boost regulator is also available in half-sized packages measuring a mere 22 x 16.5 x 6.73 mm capable of delivering up to 250 W of power.

Vicor VI chip PRM module

The high power density of PRM modules is due to Vicor’s proprietary ZVS (zero-voltage switching) topology and custom magnetics. The ZVS topology enables high-frequency switching operation—on the order of 1 MHz—with higher conversion efficiency than conventional regulators using hard switching topologies. High switching frequency reduces the size of reactive components, minimizing the required space needed for the circuitry. High switching frequency also reduces the size of the external filter components, increasing power density while enabling fast dynamic response to line and load transients. For supply-noise sensitive systems, the high switching frequency also puts the converter’s spectral artifacts beyond the band of interest for many applications.

Thanks to their versatile feedback and control capabilities, PRM modules can achieve higher power outputs by operating in arrays well into the kW range (figure 2). In addition to operating as freestanding non-isolated regulators, PRM modules can also pair with VTM™ modules—isolated current-multiplier modules—to supply high-current low-voltage loads. These arrangements can form highefficiency PoL converter topologies that drive even the lowest voltage processor or memory- subsystem supply rails from, say, a 48 V distribution bus with a single conversion stage.

New versions of the PRM module allow you to specify operating parameters through the VI Chip PRM Module Configurator, part of Vicor’s PowerBench™ online tool suite. Vicor builds unconfigured modules to stock and configures them to order. This arrangement provides modules that you’ve optimized to your system design’s requirements.

PRM module schematic

The configurator tool gives access to a substantial range of settings, providing you a great deal of flexibility to tune and optimize a power converter module to the specific needs of your application. For example, you can specify the module’s low-line, nominal, and high-line input voltages and set underand over-voltage lockout thresholds and hysteresis bands (figure 3). You can also set the output voltage, of course, but also the turnon delay and output rise time—important variables when coordinating multiple converters that serve multi-rail loads. You can also set the maximum load current. The output current-limit set point tracks this value with a 20% margin.

VI chip PRM module configurator

Another advantage of configurable modules is that they simplify the converter’s electrical interface, eliminating the external circuits that commonly establish various parametric settings. This further reduces board area and assembly costs. It also, in effect, binds the parametric settings such as output voltage, turn-on delay, ramp rate, and protection thresholds to the module instead of to external components. Keeping user-configurable parameters internal to the module reduces post assembly inspection and eliminates potentially destructive events due to, for example, WPMP (wrong part / missing part) assembly faults.

Control over the startup delay and ramp rate, coupled with a hardware enable allow modules to coordinate multiple rails natively without the added cost and development time associated with a logic block to manage the rails. Here again, you can implement even sophisticated power subsystems for processors, memory systems, and other multi-rail loads in a small area and simpler layout than with modules that control such behaviors with external components.

The configurator can generate a unique part number and data sheet that conforms to your specifications. It also immediately provides sample pricing and delivery information to help reduce scheduling and budgetary uncertainties.

Lastly, the configurator can load the device model into the PowerBench simulator, allowing you to start testing the configured PRM module’s performance within the context of its application circuit in advance of sampling (figure 4). Spend just a few minutes with the simulator and you’ll come to appreciate how much of the risk associated with a power subsystem design you can front load ahead of final component selection and sampling. The ability to simulate the power train’s performance in seconds speeds your design decisions while resolving risk factors.

Using the PRM module’s built in features and your ability to configure devices to specific applications, you can, for example, determine the sequence and timing for rails to start and stop under both normal and fault conditions. Should you, during your product’s life cycle, need to make modifications that alter the sequence, ramp timing, output voltage or any other configurable parameter, you needn’t recalculate component values or reprogram a sequence controller. Simply modify your configuration data through the online tool and generate a new part in seconds.

PowerBench Simulator

Many applications in computing, communications, and industrial spaces are increasingly demanding scalability to satisfy varying power capacity requirements with like structures. While scaling structures benefit equipment provider and customer alike, they are incompatible with discrete power designs and fast design cycles. For example, with many discrete designs, you don’t have to change the power capacity requirements more than several tens of watts before you need to re-optimize your power train component selections including power MOSFETs, inductors, and capacitors or settle for suboptimal power efficiency. By contrast, scaling power subsystems with modular components and readily accessible design-support tools allows you to experiment, simulate, and test design options with far less engineering time and provide you with an efficient, high-density, and fully specified design. Another advantage these modular converters bring, compared to a discrete design, is that the circuit board layout—typically a time consuming exercise to properly manage critical parasitic impedances in a high-speed, high-current application—is already solved within the module. Various application notes and reference designs are available to help ensure that a design realizes the module’s full performance.

The PRM modules and PowerBench toolset embody substantial power engineering intellectual property and application expertise, saving you design-cycle time, cost, complexity, and risk that so often accompany discrete designs. The combination of the power components and online design support results in devices uniquely optimized to your system design goals.

 

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