Power Electronics

Multiphase Controllers Heed Call for More Phases Per Chip

Because emerging dc-dc converters are expected to deliver up to 200 A of current at low voltages, designers are employing multiphase topology with up to eight phases and 30 A/phase to 35 A/phase. This trend has prompted suppliers to ready high-performance multiphase controllers that can deliver four or more phases from a single chip. Also, to comply with the rigorous slew rate requirements set by Intel's 10.x specifications for desktops and workstations, these multiphase controllers are implementing novel feedback techniques to accomplish ultrafast recovery time during steep step rise of load currents. As notebook power requirements surge as a result of higher functionality and faster processors, notebook power-supply designers are exploiting the latest integrated multiphase controllers to comply with the latest Intel mobile voltage positioning (IMVP) standards.

Toward that end, several key power IC suppliers have readied integrated multiphase controllers that handle four or more phases from a single chip. ON Semiconductor recently launched a family of high-performance multiphase controllers. Initial members include NCP5314 and NCP5316. NCP5314 can be programmed as a 2-, 3- or 4-phase controller tailored with per-phase switching frequency as high as 1.2 MHz. NCP5316 is a 4- to 6-phase programmable controller offering an easy upgrade path for next-generation CPUs requiring up to 200 A. NCP5314 is made to handle output currents up to 120 A. These controllers are designed to meet Intel's VR 10.x specifications with all the requisite functions and protection features.

Distributing Current

Recently, the supplier expanded this family with two devices that offer even higher performance. NCP5318 is an upgrade to 5314, and NCP5319 is an improved version of 5316. Designed to meet the latest VR 10.1 and 10.2 specs, NCP5319 can be programmed as a 4-, 5- or 6-phase buck controller with per-phase switching frequency up to 1 MHz. To compensate for variations at both line and load, as well as attain accurate current sharing between phases, both implement enhanced V2 control circuit. Hence, the current sharing between phases is within 10%. This control scheme also enables fast transient response and cuts the need for large banks of output capacitors and higher switching frequency. Per the manufacturer's data sheet, typical response time is better than 100 A/µs at 80% step load.

While pin- and function-compatible to older parts, the new versions provide improved output offset and faster response to power-good signal. The output offset voltage spec has been improved to ±9 mV, and provides tighter regulation to a narrower window of the output over the entire current range of the system. In essence, the developers have enhanced the total system accuracy of the latest members. An internal precise 6-bit digital-to-analog converter (DAC) provides a programmable voltage output from as low as 0.83 V to 1.6 V, with a tolerance of ±0.5% over the full-temperature range and input range. NCP531x features differential current sense inputs for each phase to help insure signal integrity and noise immunity in the challenged PC layouts. They also feature inductor current sensing that provides an accurate, lossless current sense scheme. In addition to providing two extra phases, the NCP5316 features per-phase current limit and pins that provide a signal scaled to both the total inductor current and the per-phase current. Other features include 0% to 100% adjustable duty cycle, programmable adaptive voltage positioning to cut output capacitor requirements and programmable soft-start. NCP5314 comes in a 32-pin Quad Flat No-lead (QFN) and a 32-pin LQFP packages, and NCP5316 is housed in a 48-pin QFN and a 48-pin LQFP, respectively.

Other companies racing to deliver more phases per chip include Analog Devices, Intersil Corp., International Rectifier, Texas Instruments, Fairchild Semiconductor, STMicroelectronics, Linear Technology and Semtech. Intersil, for instance, has unwrapped a multiphase synchronous-buck PWM controller that can be designed for up to four phases from a single IC. Optimized for AMD Athlon 64-bit processors used in notebook PCs, the ISL6244 provides a precise multiphase dc-dc converter with voltage regulation at ±1%. For precise current balancing, it employs lossless RDS(ON) current sensing. To deliver dynamic on-the-fly adjustment of core voltage over the range of 0.80 V to 1.55 V in 25-mV steps, the ISL6244 offers a 5-bit VID. Also, voltage and current feedback are actively monitored to detect fault conditions. A power-good output indicates that the controller is operating properly and the output voltage is within a set window, as determined by undervoltage and overvoltage comparators. The controller provides overcurrent protection by monitoring individual channel current and will shut down if any channel currents exceed a reference current. The ISL6244 also allows selection of channel-switching frequency in the range of 80 kHz to 1 MHz. In addition, the 32-pad QFN package, available lead-free, saves space and offers enhanced thermal efficiency.

For mobile Pentium 4 processors, Intersil has developed a 2- to 4-phase synchronous buck PWM controller with 6-bit VID input. The ISL6247 uses smart voltage regulation technology to support the Mobile Intel Pentium 4 processor's active, deep sleep and deeper sleep modes. It includes a 6-bit DAC that enables dynamic adjustment of core voltage ranging from 0.8375 V to 1.6 V in 12.5-mV steps. It also offers a thermal monitor that sends a signal to the microprocessor to reduce the load before power-system components exceed their maximum thermal limits. For design flexibility and preference, the ISL6247 supports lossless DCR, precision resistive or low-cost lossless RDS(ON) current-sensing methods. In addition, it provides a selectable channel-switching frequency ranging from 200 kHz to 1 MHz. Consequently, the ISL6247 provides flexibility in managing the balance between high-speed response, target efficiency and good thermal management. It's available in the near-chip-scale 40-pad 6-mm × 6-mm QFN package. A lead-free package version is also available.

Based on a joint development effort, Intersil and Primarion have released a digital programmable multi-phase controller that drives two to six phases from a single chip. Comprising a digital controller and corresponding power stages, the digital multiphase PowerCode architecture meets rigorous dc load line, accuracy, stability and transient response of multi-GHz CPUs. To address high-current requirements of forthcoming microprocessors, IR has launched a flexible and scalable multiphase architecture called XPhase. It supports one to X phases, with the option of choosing the number of phases, current per phase and switching frequency. The XPhase architecture lets designers add phases (one at a time) to increase output current capability as higher-speed processors become available.

Cycle-by-Cycle

TI's TPS4009x family of programmable controllers manage two, three or four phases, and offers advantages over a single power stage, including lower-current ripple on the input and output capacitors, faster transient response to load steps and improved power-handling capabilities at greater than 90% power efficiency. The TPS4009x operates each phase at a switching frequency up to 1 MHz, resulting in effective ripple frequency of up to 4 MHz at the input and output in a 4-phase application.

The controllers provide single-cycle current balance that is accurate to less than 5%. Cycle-by-cycle current sharing in output phases over the entire load allows for minimal oversizing of output FETs. For added protection of the entire system, the TPS4009x includes current-sensing fault protection, programmable overcurrent protection and individual phase-current detection. Also, a simple, adjustable voltage threshold sets current limit up to 200 A. Other features include low ripple-voltage output (< 20 mV), typical output current from 20 A to 30 A per phase, tight load regulation of 100 mV for a 50-A load step, and 100-kHz crossover frequency with 50 degrees of phase margin. Packaged in a 24-pin TSSOP, TPS4009x dc-dc controllers are available in volume.

Similarly, Analog Devices has expanded its portfolio with the addition of the ADP3168, a highly efficient multiphase synchronous-buck switching regulator controller optimized for converting a 12-V main supply into the core supply voltage required by high-performance Intel processors. Designed to provide 2- to 4-phase operation, it uses an internal 6-bit DAC to read a voltage identification (VID) code directly from the processor, which is used to set the output voltage between 0.8375 V and 1.6 V. Because it offers programmable no-load offset and slope functions to adjust the output voltage as a function of the load current, it's optimally positioned for a system transient. Other features include accurate and reliable short-circuit protection, adjustable current limiting and a delayed power-good output that accommodates on-the-fly output-voltage changes requested by the CPU. Specified over the commercial temperature range of 0°C to +85°C, it comes in a 28-lead TSSOP package.

For low-current battery-powered products, Linear Technology has readied a high-efficiency synchronous-boost converter that uses a 4-phase switching topology to minimize solution size and deliver ultralow ripple-voltage output. Designed to deliver up to 3 A of continuous output current from its thermally enhanced 5-mm × 5-mm QFN package, its 4-phase operation reduces peak inductor currents, capacitor ripple current and increases effective-switching frequency. Consequently, it minimizes both inductor and capacitor sizes, providing a total solution profile of less than 2 mm. Operating at frequencies up to 8 MHz, its internal switches provide a 5-A current limit and deliver output voltages as high as 5.25 V from an input-voltage range of 0.5 V to 4.5 V, making it suitable for Li-Ion, NiMH applications and general-purpose fixed rail systems.

The LTC3425 uses internal switches with an RDS(ON) of only 0.05 Ω to deliver efficiencies as high as 95%. Either automatic or manual burst-mode operation can be enabled to reduce no-load quiescent current to only 12 µA. Other features include antiringing control, power-good monitor, adjustable current limit, programmable soft-start, external synchronization capability and thermal protection. It comes in a 32-pin, thermally enhanced QFN package.

Analog Devices, www.analog.com CIRCLE 350 on Reader Service Card

International Rectifier, www.irf.com CIRCLE 351 on Reader Service Card

Intersil Corp., www.intersil.com CIRCLE 352 on Reader Service Card

Linear Technology Corp., www.linear.com CIRCLE 353 on Reader Service Card

On Semiconductor, www.onsemi.com CIRCLE 354 on Reader Service Card

Primarion, www.primarion.com CIRCLE 355 on Reader Service Card

Texas Instruments Inc., www.ti.com CIRCLE 356 on Reader Service Card

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