[Engineering Feature]
High Efficiency Challenges Power-Management Design
Designers face the formidable task of providing high-efficiency power management for processors that operate at 1 V and below, at 100 A or more, and at gigahertz frequencies.
The MLP 8x8 power package extends the concept of enhanced packaging. The integrated FDMF8700 module provides an additional efficiency gain of 1.5% to 2% for peak- and steadypower levels compared with discrete solutions using D-Pak packaging. The complete Fairchild family of DrMOS multichip modules includes the FDMF6700, FDMF8704, FDMF8704V, and FDMF8705 (Fig. 3).
Renesas Technology America’s R2J20602NP integrates a driver IC and high- and low-side power MOSFETs in a 56-pin quad flat no-lead (QFN) package that conforms to the integrated DrMOS package standard. This second-generation driver-MOSFET product operates at up to a 2-MHz switching frequency and has a maximum output current of 40 A. Operating at 1 MHz with VIN = 12 V and VOUT = 1.3 V, it achieves a maximum efficiency of approximately 89%. With an output current of 25 A, power loss is only 4.4 W.
The R2J20602NP complies with the European Union’s Restrictions on Hazardous Substances (RoHS) and with the DrMOS standard. Its high heat-radiation package offers a small (8 by 8 mm) mounting area. It also uses a wireless copper-plate construction technique for internal connections, reducing resistance and parasitic inductance within the package. Pins for largecurrent paths occupy most of the rear surface of the package and facilitate heat dissipation.
The NXP PIP212-12M also meets the DrMOS spec. It consists of a high side (control FET), a low side (synchronous FET), and a FET driver. The fully integrated device comes in a single surface-mount package with integral heatsink. It employs highperformance MOSFETs and a customized driver that monitors switching dead time and actively eliminates dead time without allowing the devices to go into cross conduction.
Its feature set includes functionality for sequencing. An onboard regulator provides 5 V in 12-V-only applications. Its built-in loss phase-detection circuitry suits multiphase applications. And, its VOUT sense allows current sense back to the PWM as well as multiphase current-sharing designs. With its integrated design, it can be used as the building block of buck regulators capable of greater than 30 A per phase and frequencies of up to 1 MHz per phase. Moreover, greater power densities are possible than with discrete solutions or previous integrated solutions.
MULTIPHASE PWM ICS Semtech’s SC2447 is a high-frequency, dual-phase, PWM stepdown controller optimized for Philips and Renesas DrMOS. Both phases can source or sink load currents, suiting the SC2447 for networking system power. It uses fixed-frequency, continuousconduction peak current-mode control for good compensation and fast transient response.
The SC2447 generates two independent, 180° out-of-phase, 30-A outputs. Either inductor dc resistance or a precision sense resistor can be used for current-mode control. Inductor dc resistance sensing has the advantage of being lossless. Each phase has an individual closed-loop soft-start and overload shutdown timer.
Intersil’s ISL6307A controls microprocessor core voltage regulation by driving from two to six synchronous-rectified buck channels in parallel (Fig. 3, again). Microprocessor loads can generate load transients with extremely fast edge rates. The ISL6307A features a high-bandwidth control loop and ripple frequencies up to 12 MHz to provide optimal response to the transients.
The ISL6307A senses current by utilizing patented techniques to measure the voltage across the RDS(ON) of the lower MOSFETs or dc resistance (DCR) of the output inductor during the lower MOSFET conduction intervals. Current sensing provides the needed signals for precision droop, channel-current balancing, and overcurrent protection. A programmable internal temperature compensation function compensates for the temperature coefficient of the current-sense element.
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