[Design View / Design Solution]
Learn "The Rules Of The Game" For Powering Today's Processors
Load lines and “droop” are good features to have in your power-supply-design arsenal—if you know how to apply them correctly.
DESIGN VIEW is the summary of the complete DESIGN SOLUTION contributed article, which begins on Page 2.
Rapidly evolving processors consistently challenge power-supply designers to solve complex power-delivery issues for desktops, workstations, and servers. In fact, powering the microprocessor presents the most difficult power solution in the whole computer system.
Faster transients and improved operation over temperature are just a few of the new design requirements. But the most difficult design challenge stems from the fact that the processor's specified operating-voltage tolerance keeps getting tighter and tighter. It's a bit like playing a video game in which each successive level becomes increasingly difficult. To be successful, you must first understand the rules—in this case, the processor's requirements.
But understanding these "rules of the game" means more than just memorizing the "numbers." You need to understand the requirements and potential options so that you can make better tradeoffs and decisions in your designs and products. Plus, you'll have an edge if you exploit the tricks and techniques that are available.
This article explores some of those tricks of the trade to better power delivery. For example, to simplify specifications and better define processor power requirements, Intel uses a "load-line" approach. Load line is basically an operating voltage window. If the voltage stays within the window, the power supply meets the processor specification. Another approach is a "droop" system, where the voltage decreases at a defined rate as the operating current increases.
Discussed in depth is the dynamic voltage identification (VID) spec, or VID "on-the-fly." VID allows the processor to save power by lowering its VCORE voltage while running. A voltage-regulation-module (VRM) control-chip design example is included.
HIGHLIGHTS:
"Tight Windows" Open Doors For Robust Designs
To meet performance specifications, each evolution of Intel's processors demands higher currents and tighter operating-voltage windows. This misunderstood limitation is crucial to having a robust design.
Get On The Load Line
Load line is the min-max operating voltage window that the power supply must meet over the load-current range.
"Droop" Without A Performance Slump
Droop is the slope of the load line, or the change in output voltage divided by the change in load current. Once considered a bad thing, droop, when properly applied, has become important due to the advent of high-speed transient loads in today's processors..
Sticking To The Budget
A number of items will affect a processor's operating voltage, so they must be budgeted accordingly. These include VTRANSIENT, VDROOP bus, and ripple voltage on the output capacitors caused by the inductor ripple current.
"On-The-Fly" VID
The dynamic voltage identification (VID) specification, or VID on-the-fly, makes it possible for the processor to save power. VID, a parallel digital word, tells the voltage regulator what to output.
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