Power Management In A Gigahertz World
Power supplies have evolved significantly over the last 50 years. But a major "step function" transition occurred with the introduction of the first monolithic bipolar pulse-width modulator (PWM) IC by Silicon General in the early '70s. As it opened the door to using ICs in power-supply designs, it also motivated designers toward switching techniques. Along came power MOSFETs to further aid this transition. Today, switch-mode converters are in the mainstream, and they're way ahead of older linear techniques.
Simultaneously, bipolar PWMs have migrated to CMOS and biCMOS chips with an amazing level of integration density on-board to deliver one-chip solutions for many applications. Dictated by the energy saving needs of modern systems and battery-powered handheld appliances, a variety of power saving techniques have been implemented in these devices over the years. Also during the last few decades, the simple PWM controller has developed into many other forms, like switching regulators, low-dropout regulators (LDOs), dc-dc converters, and other similar devices to cater to the needs of emerging applications. Each of these devices is further taking advantage of process improvements to implement new levels of integration and higher performance in a smaller package, at a lower cost.
Now, the next generation poses a new set of issues and hurdles. As microprocessors and CPUs in the upcoming computers and communication systems migrate toward multigigahertz clock speeds, with core voltages dropping below 1 V and current demands approaching 100 A, power is crucial to the success of the product. It must be managed optimally to make a product useful.
These challenges are pushing suppliers toward newer topologies like multiphase controllers, multigigahertz regulators, and digital architectures. Just as semiconductor devices have managed power efficiently until now, they're poised to meet the challenges of the future. Processes and topologies will work hand in hand to deliver new levels of performance that were considered impractical even in the recent past.
As PWM power controllers move up the frequency scale, they're experiencing increased integration. With the trend toward multiple voltage outputs from one low-cost package, suppliers are combining dual synchronous buck controllers on-chip to provide 3.3- and 5-V outputs, which are adjustable as well. In addition, these controllers include drivers for high-speed MOSFETs and provide all necessary control and safety features. Some also come with multiple LDOs on the same die. Current-mode PWM controllers are being crafted to handle large input voltages (up to 180 V), especially for the telecom sector. In this application, they're primarily aimed at converting 48 V to logic-level outputs. Finally, for mobile CPUs, synchronous PWM buck controllers will come with built-in DACs to dynamically program the output.
Efforts continue to get more juice from miniature conventional packages. For instance, STMicroelectronics has modified the ubiquitous SO8 package for monolithic switching regulators to let it handle more output current. By connecting the sync and VREF pins to ground and using an exposed frame, the popular SO8 will accommodate step-down converters with up to 2-A current-handling capability. Simultaneously, the body of the SC70 is being widened to accommodate chips that are nearly five times larger in the same footprint. So expect a number of LDOs and other power-management ICs in the widebody j-lead SC70 or SC70JW starting this year. Startup Analogic Tech (www.analogictech.com) has plans for it.
Higher current at lower voltages and faster transient response are key factors pushing power-supply designers toward multiphase controllers. Several suppliers have introduced parts for this application. As the multiphase adoption expands, more power IC makers should announce solutions for this market. Intersil (www.intersil.com), for example, is exploring digitally controlled multiphase controllers for future multigigahertz processors. Toward this end, Intersil has licensed Primarion's (www.primarion.com) proprietary digital power architecture to develop new power controllers for future multigigahertz processors expected to approach 10 GHz in the next few years. STMicroelectronics (www.st.com) will introduce scalable interleaved multiphase controllers that are compliant with Intel's (www.intel.com) VRM 9.1 specs and capable of handling up to eight phases. International Rectifier (www.irf.com) also is ready to announce its parts for the application.
An expanding need for voltage doubling in handheld color displays and other battery-powered appliances is driving the use of charge-pumps in these applications. The new capless charge pumps also include power MOSFETs and control circuitry on-chip to minimize board space. They will be offered in tiny packages like the SC70.
New lines of personal digital assistants (PDAs), digital cameras, and other handheld electronic products are using a number of voltages throughout the system. Therefore, multiple switching regulators and LDOs are used in such systems to meet the multivoltage requirements. A single multi-output programmable switching regulator (PSR) can now replace multiple conventional switching regulators in these applications and significantly lower the component count and cost of these devices. In addition, the PSR will offer communication links to the system's host processor. Fabless design house iWatt is working to extend its new pulseTrain digital technique to PSRs, with plans to introduce products this year.
As microprocessor speed moves to 10 GHz in a few years, and as core voltages drop with every CMOS generation while current requirements climb, it's time to change the Intel mobile voltage position (IMVP) specs. The current IMVP III is expected to evolve to IMVP IV this year to meet the stringent voltage, current, and transient response requirements of forthcoming processors.
Implementing digital techniques, a new breed of power-supply controller is in preparation. It's expected to overcome the limitations of traditional PWM and other analog methods, and to provide a big performance boost to ac-dc and dc-dc isolated and nonisolated supplies. Aside from delivering flexibility and robustness, the digital SMPS controller maintains high efficiency across all line and load conditions. Startup iWatt (www.iwatt.com) has shown that ac-dc converters built with its latest digital controller can deliver power-conversion efficiency in excess of 85% across all line and load variations. Such a controller also offers built-in active power-factor-correction (PFC) circuitry for ac-dc applications of up to 250 W.
There's a lot more room to improve, both linear and switching, low-dropout regulators. So some newcomers like Analogic Tech Inc. (www.analogictech.com) as well as Micrel Semiconductor (www.micrel.com) are focused on reducing the ground current from about 4 µA today to an extremely low value of about 1 µA in the near future for the low-output current LDO devices. Similarly, ultra-low-dropout linear regulators are being streamlined to handle more output current while keeping the on-resistance to a minimum.
To permit safe insertion and removal of line cards with multiple supplies from a live backplane, suppliers are packing dual hot-swap controllers in a single package with features to protect the load against overcurrent and load transients. Newer products will include support for two or more PCI slots and provide an SMBus interface for slot power control and status.
Integrated offline controllers have provided high-voltage capability for building ac-dc converters from one chip for standby power supplies or battery chargers with 50 W or less power. Now these controllers are being streamlined to handle up to 250 W from a single package with a universal input. In addition, they will combine PFC circuitry on the same chip.